Merge keyserver & userapi (#2972)

As discussed yesterday, a first draft of merging the keyserver and the
userapi.

54 files changed, 6550 insertions, 90 deletions

diff --git a/userapi/api/api.go b/userapi/api/api.go
index 4ea2e91c..fa297f77 100644
--- a/userapi/api/api.go
+++ b/userapi/api/api.go
@@ -15,9 +15,13 @@
 package api
 
 import (
+	"bytes"
 	"context"
 	"encoding/json"
+	"strings"
+	"time"
 
+	"github.com/matrix-org/dendrite/userapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
 
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
@@ -26,15 +30,12 @@ import (
 
 // UserInternalAPI is the internal API for information about users and devices.
 type UserInternalAPI interface {
-	AppserviceUserAPI
 	SyncUserAPI
 	ClientUserAPI
-	MediaUserAPI
 	FederationUserAPI
-	RoomserverUserAPI
-	KeyserverUserAPI
 
 	QuerySearchProfilesAPI // used by p2p demos
+	QueryAccountByLocalpart(ctx context.Context, req *QueryAccountByLocalpartRequest, res *QueryAccountByLocalpartResponse) (err error)
 }
 
 // api functions required by the appservice api
@@ -43,11 +44,6 @@ type AppserviceUserAPI interface {
 	PerformDeviceCreation(ctx context.Context, req *PerformDeviceCreationRequest, res *PerformDeviceCreationResponse) error
 }
 
-type KeyserverUserAPI interface {
-	QueryDevices(ctx context.Context, req *QueryDevicesRequest, res *QueryDevicesResponse) error
-	QueryDeviceInfos(ctx context.Context, req *QueryDeviceInfosRequest, res *QueryDeviceInfosResponse) error
-}
-
 type RoomserverUserAPI interface {
 	QueryAccountData(ctx context.Context, req *QueryAccountDataRequest, res *QueryAccountDataResponse) error
 	QueryAccountByLocalpart(ctx context.Context, req *QueryAccountByLocalpartRequest, res *QueryAccountByLocalpartResponse) (err error)
@@ -60,13 +56,20 @@ type MediaUserAPI interface {
 
 // api functions required by the federation api
 type FederationUserAPI interface {
+	UploadDeviceKeysAPI
 	QueryOpenIDToken(ctx context.Context, req *QueryOpenIDTokenRequest, res *QueryOpenIDTokenResponse) error
 	QueryProfile(ctx context.Context, req *QueryProfileRequest, res *QueryProfileResponse) error
+	QueryDevices(ctx context.Context, req *QueryDevicesRequest, res *QueryDevicesResponse) error
+	QueryKeys(ctx context.Context, req *QueryKeysRequest, res *QueryKeysResponse) error
+	QuerySignatures(ctx context.Context, req *QuerySignaturesRequest, res *QuerySignaturesResponse) error
+	QueryDeviceMessages(ctx context.Context, req *QueryDeviceMessagesRequest, res *QueryDeviceMessagesResponse) error
+	PerformClaimKeys(ctx context.Context, req *PerformClaimKeysRequest, res *PerformClaimKeysResponse) error
 }
 
 // api functions required by the sync api
 type SyncUserAPI interface {
 	QueryAcccessTokenAPI
+	SyncKeyAPI
 	QueryAccountData(ctx context.Context, req *QueryAccountDataRequest, res *QueryAccountDataResponse) error
 	PerformLastSeenUpdate(ctx context.Context, req *PerformLastSeenUpdateRequest, res *PerformLastSeenUpdateResponse) error
 	PerformDeviceUpdate(ctx context.Context, req *PerformDeviceUpdateRequest, res *PerformDeviceUpdateResponse) error
@@ -79,6 +82,7 @@ type ClientUserAPI interface {
 	QueryAcccessTokenAPI
 	LoginTokenInternalAPI
 	UserLoginAPI
+	ClientKeyAPI
 	QueryNumericLocalpart(ctx context.Context, req *QueryNumericLocalpartRequest, res *QueryNumericLocalpartResponse) error
 	QueryDevices(ctx context.Context, req *QueryDevicesRequest, res *QueryDevicesResponse) error
 	QueryProfile(ctx context.Context, req *QueryProfileRequest, res *QueryProfileResponse) error
@@ -681,3 +685,310 @@ type QueryAccountByLocalpartRequest struct {
 type QueryAccountByLocalpartResponse struct {
 	Account *Account
 }
+
+// API functions required by the clientapi
+type ClientKeyAPI interface {
+	UploadDeviceKeysAPI
+	QueryKeys(ctx context.Context, req *QueryKeysRequest, res *QueryKeysResponse) error
+	PerformUploadKeys(ctx context.Context, req *PerformUploadKeysRequest, res *PerformUploadKeysResponse) error
+
+	PerformUploadDeviceSignatures(ctx context.Context, req *PerformUploadDeviceSignaturesRequest, res *PerformUploadDeviceSignaturesResponse) error
+	// PerformClaimKeys claims one-time keys for use in pre-key messages
+	PerformClaimKeys(ctx context.Context, req *PerformClaimKeysRequest, res *PerformClaimKeysResponse) error
+	PerformMarkAsStaleIfNeeded(ctx context.Context, req *PerformMarkAsStaleRequest, res *struct{}) error
+}
+
+type UploadDeviceKeysAPI interface {
+	PerformUploadDeviceKeys(ctx context.Context, req *PerformUploadDeviceKeysRequest, res *PerformUploadDeviceKeysResponse) error
+}
+
+// API functions required by the syncapi
+type SyncKeyAPI interface {
+	QueryKeyChanges(ctx context.Context, req *QueryKeyChangesRequest, res *QueryKeyChangesResponse) error
+	QueryOneTimeKeys(ctx context.Context, req *QueryOneTimeKeysRequest, res *QueryOneTimeKeysResponse) error
+	PerformMarkAsStaleIfNeeded(ctx context.Context, req *PerformMarkAsStaleRequest, res *struct{}) error
+}
+
+type FederationKeyAPI interface {
+	UploadDeviceKeysAPI
+	QueryKeys(ctx context.Context, req *QueryKeysRequest, res *QueryKeysResponse) error
+	QuerySignatures(ctx context.Context, req *QuerySignaturesRequest, res *QuerySignaturesResponse) error
+	QueryDeviceMessages(ctx context.Context, req *QueryDeviceMessagesRequest, res *QueryDeviceMessagesResponse) error
+	PerformClaimKeys(ctx context.Context, req *PerformClaimKeysRequest, res *PerformClaimKeysResponse) error
+}
+
+// KeyError is returned if there was a problem performing/querying the server
+type KeyError struct {
+	Err                string `json:"error"`
+	IsInvalidSignature bool   `json:"is_invalid_signature,omitempty"` // M_INVALID_SIGNATURE
+	IsMissingParam     bool   `json:"is_missing_param,omitempty"`     // M_MISSING_PARAM
+	IsInvalidParam     bool   `json:"is_invalid_param,omitempty"`     // M_INVALID_PARAM
+}
+
+func (k *KeyError) Error() string {
+	return k.Err
+}
+
+type DeviceMessageType int
+
+const (
+	TypeDeviceKeyUpdate DeviceMessageType = iota
+	TypeCrossSigningUpdate
+)
+
+// DeviceMessage represents the message produced into Kafka by the key server.
+type DeviceMessage struct {
+	Type                         DeviceMessageType `json:"Type,omitempty"`
+	*DeviceKeys                  `json:"DeviceKeys,omitempty"`
+	*OutputCrossSigningKeyUpdate `json:"CrossSigningKeyUpdate,omitempty"`
+	// A monotonically increasing number which represents device changes for this user.
+	StreamID       int64
+	DeviceChangeID int64
+}
+
+// OutputCrossSigningKeyUpdate is an entry in the signing key update output kafka log
+type OutputCrossSigningKeyUpdate struct {
+	CrossSigningKeyUpdate `json:"signing_keys"`
+}
+
+type CrossSigningKeyUpdate struct {
+	MasterKey      *gomatrixserverlib.CrossSigningKey `json:"master_key,omitempty"`
+	SelfSigningKey *gomatrixserverlib.CrossSigningKey `json:"self_signing_key,omitempty"`
+	UserID         string                             `json:"user_id"`
+}
+
+// DeviceKeysEqual returns true if the device keys updates contain the
+// same display name and key JSON. This will return false if either of
+// the updates is not a device keys update, or if the user ID/device ID
+// differ between the two.
+func (m1 *DeviceMessage) DeviceKeysEqual(m2 *DeviceMessage) bool {
+	if m1.DeviceKeys == nil || m2.DeviceKeys == nil {
+		return false
+	}
+	if m1.UserID != m2.UserID || m1.DeviceID != m2.DeviceID {
+		return false
+	}
+	if m1.DisplayName != m2.DisplayName {
+		return false // different display names
+	}
+	if len(m1.KeyJSON) == 0 || len(m2.KeyJSON) == 0 {
+		return false // either is empty
+	}
+	return bytes.Equal(m1.KeyJSON, m2.KeyJSON)
+}
+
+// DeviceKeys represents a set of device keys for a single device
+// https://matrix.org/docs/spec/client_server/r0.6.1#post-matrix-client-r0-keys-upload
+type DeviceKeys struct {
+	// The user who owns this device
+	UserID string
+	// The device ID of this device
+	DeviceID string
+	// The device display name
+	DisplayName string
+	// The raw device key JSON
+	KeyJSON []byte
+}
+
+// WithStreamID returns a copy of this device message with the given stream ID
+func (k *DeviceKeys) WithStreamID(streamID int64) DeviceMessage {
+	return DeviceMessage{
+		DeviceKeys: k,
+		StreamID:   streamID,
+	}
+}
+
+// OneTimeKeys represents a set of one-time keys for a single device
+// https://matrix.org/docs/spec/client_server/r0.6.1#post-matrix-client-r0-keys-upload
+type OneTimeKeys struct {
+	// The user who owns this device
+	UserID string
+	// The device ID of this device
+	DeviceID string
+	// A map of algorithm:key_id => key JSON
+	KeyJSON map[string]json.RawMessage
+}
+
+// Split a key in KeyJSON into algorithm and key ID
+func (k *OneTimeKeys) Split(keyIDWithAlgo string) (algo string, keyID string) {
+	segments := strings.Split(keyIDWithAlgo, ":")
+	return segments[0], segments[1]
+}
+
+// OneTimeKeysCount represents the counts of one-time keys for a single device
+type OneTimeKeysCount struct {
+	// The user who owns this device
+	UserID string
+	// The device ID of this device
+	DeviceID string
+	// algorithm to count e.g:
+	// {
+	//   "curve25519": 10,
+	//   "signed_curve25519": 20
+	// }
+	KeyCount map[string]int
+}
+
+// PerformUploadKeysRequest is the request to PerformUploadKeys
+type PerformUploadKeysRequest struct {
+	UserID      string // Required - User performing the request
+	DeviceID    string // Optional - Device performing the request, for fetching OTK count
+	DeviceKeys  []DeviceKeys
+	OneTimeKeys []OneTimeKeys
+	// OnlyDisplayNameUpdates should be `true` if ALL the DeviceKeys are present to update
+	// the display name for their respective device, and NOT to modify the keys. The key
+	// itself doesn't change but it's easier to pretend upload new keys and reuse the same code paths.
+	// Without this flag, requests to modify device display names would delete device keys.
+	OnlyDisplayNameUpdates bool
+}
+
+// PerformUploadKeysResponse is the response to PerformUploadKeys
+type PerformUploadKeysResponse struct {
+	// A fatal error when processing e.g database failures
+	Error *KeyError
+	// A map of user_id -> device_id -> Error for tracking failures.
+	KeyErrors        map[string]map[string]*KeyError
+	OneTimeKeyCounts []OneTimeKeysCount
+}
+
+// PerformDeleteKeysRequest asks the keyserver to forget about certain
+// keys, and signatures related to those keys.
+type PerformDeleteKeysRequest struct {
+	UserID string
+	KeyIDs []gomatrixserverlib.KeyID
+}
+
+// PerformDeleteKeysResponse is the response to PerformDeleteKeysRequest.
+type PerformDeleteKeysResponse struct {
+	Error *KeyError
+}
+
+// KeyError sets a key error field on KeyErrors
+func (r *PerformUploadKeysResponse) KeyError(userID, deviceID string, err *KeyError) {
+	if r.KeyErrors[userID] == nil {
+		r.KeyErrors[userID] = make(map[string]*KeyError)
+	}
+	r.KeyErrors[userID][deviceID] = err
+}
+
+type PerformClaimKeysRequest struct {
+	// Map of user_id to device_id to algorithm name
+	OneTimeKeys map[string]map[string]string
+	Timeout     time.Duration
+}
+
+type PerformClaimKeysResponse struct {
+	// Map of user_id to device_id to algorithm:key_id to key JSON
+	OneTimeKeys map[string]map[string]map[string]json.RawMessage
+	// Map of remote server domain to error JSON
+	Failures map[string]interface{}
+	// Set if there was a fatal error processing this action
+	Error *KeyError
+}
+
+type PerformUploadDeviceKeysRequest struct {
+	gomatrixserverlib.CrossSigningKeys
+	// The user that uploaded the key, should be populated by the clientapi.
+	UserID string
+}
+
+type PerformUploadDeviceKeysResponse struct {
+	Error *KeyError
+}
+
+type PerformUploadDeviceSignaturesRequest struct {
+	Signatures map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice
+	// The user that uploaded the sig, should be populated by the clientapi.
+	UserID string
+}
+
+type PerformUploadDeviceSignaturesResponse struct {
+	Error *KeyError
+}
+
+type QueryKeysRequest struct {
+	// The user ID asking for the keys, e.g. if from a client API request.
+	// Will not be populated if the key request came from federation.
+	UserID string
+	// Maps user IDs to a list of devices
+	UserToDevices map[string][]string
+	Timeout       time.Duration
+}
+
+type QueryKeysResponse struct {
+	// Map of remote server domain to error JSON
+	Failures map[string]interface{}
+	// Map of user_id to device_id to device_key
+	DeviceKeys map[string]map[string]json.RawMessage
+	// Maps of user_id to cross signing key
+	MasterKeys      map[string]gomatrixserverlib.CrossSigningKey
+	SelfSigningKeys map[string]gomatrixserverlib.CrossSigningKey
+	UserSigningKeys map[string]gomatrixserverlib.CrossSigningKey
+	// Set if there was a fatal error processing this query
+	Error *KeyError
+}
+
+type QueryKeyChangesRequest struct {
+	// The offset of the last received key event, or sarama.OffsetOldest if this is from the beginning
+	Offset int64
+	// The inclusive offset where to track key changes up to. Messages with this offset are included in the response.
+	// Use types.OffsetNewest if the offset is unknown (then check the response Offset to avoid racing).
+	ToOffset int64
+}
+
+type QueryKeyChangesResponse struct {
+	// The set of users who have had their keys change.
+	UserIDs []string
+	// The latest offset represented in this response.
+	Offset int64
+	// Set if there was a problem handling the request.
+	Error *KeyError
+}
+
+type QueryOneTimeKeysRequest struct {
+	// The local user to query OTK counts for
+	UserID string
+	// The device to query OTK counts for
+	DeviceID string
+}
+
+type QueryOneTimeKeysResponse struct {
+	// OTK key counts, in the extended /sync form described by https://matrix.org/docs/spec/client_server/r0.6.1#id84
+	Count OneTimeKeysCount
+	Error *KeyError
+}
+
+type QueryDeviceMessagesRequest struct {
+	UserID string
+}
+
+type QueryDeviceMessagesResponse struct {
+	// The latest stream ID
+	StreamID int64
+	Devices  []DeviceMessage
+	Error    *KeyError
+}
+
+type QuerySignaturesRequest struct {
+	// A map of target user ID -> target key/device IDs to retrieve signatures for
+	TargetIDs map[string][]gomatrixserverlib.KeyID `json:"target_ids"`
+}
+
+type QuerySignaturesResponse struct {
+	// A map of target user ID -> target key/device ID -> origin user ID -> origin key/device ID -> signatures
+	Signatures map[string]map[gomatrixserverlib.KeyID]types.CrossSigningSigMap
+	// A map of target user ID -> cross-signing master key
+	MasterKeys map[string]gomatrixserverlib.CrossSigningKey
+	// A map of target user ID -> cross-signing self-signing key
+	SelfSigningKeys map[string]gomatrixserverlib.CrossSigningKey
+	// A map of target user ID -> cross-signing user-signing key
+	UserSigningKeys map[string]gomatrixserverlib.CrossSigningKey
+	// The request error, if any
+	Error *KeyError
+}
+
+type PerformMarkAsStaleRequest struct {
+	UserID   string
+	Domain   gomatrixserverlib.ServerName
+	DeviceID string
+}
diff --git a/userapi/consumers/clientapi.go b/userapi/consumers/clientapi.go
index 42ae72e7..51bd2753 100644
--- a/userapi/consumers/clientapi.go
+++ b/userapi/consumers/clientapi.go
@@ -37,7 +37,7 @@ type OutputReceiptEventConsumer struct {
 	jetstream    nats.JetStreamContext
 	durable      string
 	topic        string
-	db           storage.Database
+	db           storage.UserDatabase
 	serverName   gomatrixserverlib.ServerName
 	syncProducer *producers.SyncAPI
 	pgClient     pushgateway.Client
@@ -49,7 +49,7 @@ func NewOutputReceiptEventConsumer(
 	process *process.ProcessContext,
 	cfg *config.UserAPI,
 	js nats.JetStreamContext,
-	store storage.Database,
+	store storage.UserDatabase,
 	syncProducer *producers.SyncAPI,
 	pgClient pushgateway.Client,
 ) *OutputReceiptEventConsumer {
diff --git a/userapi/consumers/devicelistupdate.go b/userapi/consumers/devicelistupdate.go
new file mode 100644
index 00000000..a65889fc
--- /dev/null
+++ b/userapi/consumers/devicelistupdate.go
@@ -0,0 +1,95 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package consumers
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/matrix-org/dendrite/userapi/internal"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/nats-io/nats.go"
+	"github.com/sirupsen/logrus"
+
+	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/dendrite/setup/jetstream"
+	"github.com/matrix-org/dendrite/setup/process"
+)
+
+// DeviceListUpdateConsumer consumes device list updates that came in over federation.
+type DeviceListUpdateConsumer struct {
+	ctx               context.Context
+	jetstream         nats.JetStreamContext
+	durable           string
+	topic             string
+	updater           *internal.DeviceListUpdater
+	isLocalServerName func(gomatrixserverlib.ServerName) bool
+}
+
+// NewDeviceListUpdateConsumer creates a new DeviceListConsumer. Call Start() to begin consuming from key servers.
+func NewDeviceListUpdateConsumer(
+	process *process.ProcessContext,
+	cfg *config.UserAPI,
+	js nats.JetStreamContext,
+	updater *internal.DeviceListUpdater,
+) *DeviceListUpdateConsumer {
+	return &DeviceListUpdateConsumer{
+		ctx:               process.Context(),
+		jetstream:         js,
+		durable:           cfg.Matrix.JetStream.Prefixed("KeyServerInputDeviceListConsumer"),
+		topic:             cfg.Matrix.JetStream.Prefixed(jetstream.InputDeviceListUpdate),
+		updater:           updater,
+		isLocalServerName: cfg.Matrix.IsLocalServerName,
+	}
+}
+
+// Start consuming from key servers
+func (t *DeviceListUpdateConsumer) Start() error {
+	return jetstream.JetStreamConsumer(
+		t.ctx, t.jetstream, t.topic, t.durable, 1,
+		t.onMessage, nats.DeliverAll(), nats.ManualAck(),
+	)
+}
+
+// onMessage is called in response to a message received on the
+// key change events topic from the key server.
+func (t *DeviceListUpdateConsumer) onMessage(ctx context.Context, msgs []*nats.Msg) bool {
+	msg := msgs[0] // Guaranteed to exist if onMessage is called
+	var m gomatrixserverlib.DeviceListUpdateEvent
+	if err := json.Unmarshal(msg.Data, &m); err != nil {
+		logrus.WithError(err).Errorf("Failed to read from device list update input topic")
+		return true
+	}
+	origin := gomatrixserverlib.ServerName(msg.Header.Get("origin"))
+	if _, serverName, err := gomatrixserverlib.SplitID('@', m.UserID); err != nil {
+		return true
+	} else if t.isLocalServerName(serverName) {
+		return true
+	} else if serverName != origin {
+		return true
+	}
+
+	err := t.updater.Update(ctx, m)
+	if err != nil {
+		logrus.WithFields(logrus.Fields{
+			"user_id":   m.UserID,
+			"device_id": m.DeviceID,
+			"stream_id": m.StreamID,
+			"prev_id":   m.PrevID,
+		}).WithError(err).Errorf("Failed to update device list")
+		return false
+	}
+	return true
+}
diff --git a/userapi/consumers/roomserver.go b/userapi/consumers/roomserver.go
index 3ce5af62..47d33095 100644
--- a/userapi/consumers/roomserver.go
+++ b/userapi/consumers/roomserver.go
@@ -38,7 +38,7 @@ type OutputRoomEventConsumer struct {
 	rsAPI        rsapi.UserRoomserverAPI
 	jetstream    nats.JetStreamContext
 	durable      string
-	db           storage.Database
+	db           storage.UserDatabase
 	topic        string
 	pgClient     pushgateway.Client
 	syncProducer *producers.SyncAPI
@@ -53,7 +53,7 @@ func NewOutputRoomEventConsumer(
 	process *process.ProcessContext,
 	cfg *config.UserAPI,
 	js nats.JetStreamContext,
-	store storage.Database,
+	store storage.UserDatabase,
 	pgClient pushgateway.Client,
 	rsAPI rsapi.UserRoomserverAPI,
 	syncProducer *producers.SyncAPI,
diff --git a/userapi/consumers/roomserver_test.go b/userapi/consumers/roomserver_test.go
index 39f4aab4..bc5ae652 100644
--- a/userapi/consumers/roomserver_test.go
+++ b/userapi/consumers/roomserver_test.go
@@ -18,11 +18,11 @@ import (
 	userAPITypes "github.com/matrix-org/dendrite/userapi/types"
 )
 
-func mustCreateDatabase(t *testing.T, dbType test.DBType) (storage.Database, func()) {
+func mustCreateDatabase(t *testing.T, dbType test.DBType) (storage.UserDatabase, func()) {
 	base, baseclose := testrig.CreateBaseDendrite(t, dbType)
 	t.Helper()
 	connStr, close := test.PrepareDBConnectionString(t, dbType)
-	db, err := storage.NewUserAPIDatabase(base, &config.DatabaseOptions{
+	db, err := storage.NewUserDatabase(base, &config.DatabaseOptions{
 		ConnectionString: config.DataSource(connStr),
 	}, "", 4, 0, 0, "")
 	if err != nil {
diff --git a/userapi/consumers/signingkeyupdate.go b/userapi/consumers/signingkeyupdate.go
new file mode 100644
index 00000000..f4ff017d
--- /dev/null
+++ b/userapi/consumers/signingkeyupdate.go
@@ -0,0 +1,111 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package consumers
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/nats-io/nats.go"
+	"github.com/sirupsen/logrus"
+
+	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/dendrite/setup/jetstream"
+	"github.com/matrix-org/dendrite/setup/process"
+	"github.com/matrix-org/dendrite/userapi/api"
+)
+
+// SigningKeyUpdateConsumer consumes signing key updates that came in over federation.
+type SigningKeyUpdateConsumer struct {
+	ctx               context.Context
+	jetstream         nats.JetStreamContext
+	durable           string
+	topic             string
+	userAPI           api.UploadDeviceKeysAPI
+	cfg               *config.UserAPI
+	isLocalServerName func(gomatrixserverlib.ServerName) bool
+}
+
+// NewSigningKeyUpdateConsumer creates a new SigningKeyUpdateConsumer. Call Start() to begin consuming from key servers.
+func NewSigningKeyUpdateConsumer(
+	process *process.ProcessContext,
+	cfg *config.UserAPI,
+	js nats.JetStreamContext,
+	userAPI api.UploadDeviceKeysAPI,
+) *SigningKeyUpdateConsumer {
+	return &SigningKeyUpdateConsumer{
+		ctx:               process.Context(),
+		jetstream:         js,
+		durable:           cfg.Matrix.JetStream.Prefixed("KeyServerSigningKeyConsumer"),
+		topic:             cfg.Matrix.JetStream.Prefixed(jetstream.InputSigningKeyUpdate),
+		userAPI:           userAPI,
+		cfg:               cfg,
+		isLocalServerName: cfg.Matrix.IsLocalServerName,
+	}
+}
+
+// Start consuming from key servers
+func (t *SigningKeyUpdateConsumer) Start() error {
+	return jetstream.JetStreamConsumer(
+		t.ctx, t.jetstream, t.topic, t.durable, 1,
+		t.onMessage, nats.DeliverAll(), nats.ManualAck(),
+	)
+}
+
+// onMessage is called in response to a message received on the
+// signing key update events topic from the key server.
+func (t *SigningKeyUpdateConsumer) onMessage(ctx context.Context, msgs []*nats.Msg) bool {
+	msg := msgs[0] // Guaranteed to exist if onMessage is called
+	var updatePayload api.CrossSigningKeyUpdate
+	if err := json.Unmarshal(msg.Data, &updatePayload); err != nil {
+		logrus.WithError(err).Errorf("Failed to read from signing key update input topic")
+		return true
+	}
+	origin := gomatrixserverlib.ServerName(msg.Header.Get("origin"))
+	if _, serverName, err := gomatrixserverlib.SplitID('@', updatePayload.UserID); err != nil {
+		logrus.WithError(err).Error("failed to split user id")
+		return true
+	} else if t.isLocalServerName(serverName) {
+		logrus.Warn("dropping device key update from ourself")
+		return true
+	} else if serverName != origin {
+		logrus.Warnf("dropping device key update, %s != %s", serverName, origin)
+		return true
+	}
+
+	keys := gomatrixserverlib.CrossSigningKeys{}
+	if updatePayload.MasterKey != nil {
+		keys.MasterKey = *updatePayload.MasterKey
+	}
+	if updatePayload.SelfSigningKey != nil {
+		keys.SelfSigningKey = *updatePayload.SelfSigningKey
+	}
+	uploadReq := &api.PerformUploadDeviceKeysRequest{
+		CrossSigningKeys: keys,
+		UserID:           updatePayload.UserID,
+	}
+	uploadRes := &api.PerformUploadDeviceKeysResponse{}
+	if err := t.userAPI.PerformUploadDeviceKeys(ctx, uploadReq, uploadRes); err != nil {
+		logrus.WithError(err).Error("failed to upload device keys")
+		return false
+	}
+	if uploadRes.Error != nil {
+		logrus.WithError(uploadRes.Error).Error("failed to upload device keys")
+		return true
+	}
+
+	return true
+}
diff --git a/userapi/internal/cross_signing.go b/userapi/internal/cross_signing.go
new file mode 100644
index 00000000..8b9704d1
--- /dev/null
+++ b/userapi/internal/cross_signing.go
@@ -0,0 +1,587 @@
+// Copyright 2021 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import (
+	"bytes"
+	"context"
+	"crypto/ed25519"
+	"database/sql"
+	"fmt"
+	"strings"
+
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+	"golang.org/x/crypto/curve25519"
+)
+
+func sanityCheckKey(key gomatrixserverlib.CrossSigningKey, userID string, purpose gomatrixserverlib.CrossSigningKeyPurpose) error {
+	// Is there exactly one key?
+	if len(key.Keys) != 1 {
+		return fmt.Errorf("should contain exactly one key")
+	}
+
+	// Does the key ID match the key value? Iterates exactly once
+	for keyID, keyData := range key.Keys {
+		b64 := keyData.Encode()
+		tokens := strings.Split(string(keyID), ":")
+		if len(tokens) != 2 {
+			return fmt.Errorf("key ID is incorrectly formatted")
+		}
+		if tokens[1] != b64 {
+			return fmt.Errorf("key ID isn't correct")
+		}
+		switch tokens[0] {
+		case "ed25519":
+			if len(keyData) != ed25519.PublicKeySize {
+				return fmt.Errorf("ed25519 key is not the correct length")
+			}
+		case "curve25519":
+			if len(keyData) != curve25519.PointSize {
+				return fmt.Errorf("curve25519 key is not the correct length")
+			}
+		default:
+			// We can't enforce the key length to be correct for an
+			// algorithm that we don't recognise, so instead we'll
+			// just make sure that it isn't incredibly excessive.
+			if l := len(keyData); l > 4096 {
+				return fmt.Errorf("unknown key type is too long (%d bytes)", l)
+			}
+		}
+	}
+
+	// Check to see if the signatures make sense
+	for _, forOriginUser := range key.Signatures {
+		for originKeyID, originSignature := range forOriginUser {
+			switch strings.SplitN(string(originKeyID), ":", 1)[0] {
+			case "ed25519":
+				if len(originSignature) != ed25519.SignatureSize {
+					return fmt.Errorf("ed25519 signature is not the correct length")
+				}
+			case "curve25519":
+				return fmt.Errorf("curve25519 signatures are impossible")
+			default:
+				if l := len(originSignature); l > 4096 {
+					return fmt.Errorf("unknown signature type is too long (%d bytes)", l)
+				}
+			}
+		}
+	}
+
+	// Does the key claim to be from the right user?
+	if userID != key.UserID {
+		return fmt.Errorf("key has a user ID mismatch")
+	}
+
+	// Does the key contain the correct purpose?
+	useful := false
+	for _, usage := range key.Usage {
+		if usage == purpose {
+			useful = true
+			break
+		}
+	}
+	if !useful {
+		return fmt.Errorf("key does not contain correct usage purpose")
+	}
+
+	return nil
+}
+
+// nolint:gocyclo
+func (a *UserInternalAPI) PerformUploadDeviceKeys(ctx context.Context, req *api.PerformUploadDeviceKeysRequest, res *api.PerformUploadDeviceKeysResponse) error {
+	// Find the keys to store.
+	byPurpose := map[gomatrixserverlib.CrossSigningKeyPurpose]gomatrixserverlib.CrossSigningKey{}
+	toStore := types.CrossSigningKeyMap{}
+	hasMasterKey := false
+
+	if len(req.MasterKey.Keys) > 0 {
+		if err := sanityCheckKey(req.MasterKey, req.UserID, gomatrixserverlib.CrossSigningKeyPurposeMaster); err != nil {
+			res.Error = &api.KeyError{
+				Err:            "Master key sanity check failed: " + err.Error(),
+				IsInvalidParam: true,
+			}
+			return nil
+		}
+
+		byPurpose[gomatrixserverlib.CrossSigningKeyPurposeMaster] = req.MasterKey
+		for _, key := range req.MasterKey.Keys { // iterates once, see sanityCheckKey
+			toStore[gomatrixserverlib.CrossSigningKeyPurposeMaster] = key
+		}
+		hasMasterKey = true
+	}
+
+	if len(req.SelfSigningKey.Keys) > 0 {
+		if err := sanityCheckKey(req.SelfSigningKey, req.UserID, gomatrixserverlib.CrossSigningKeyPurposeSelfSigning); err != nil {
+			res.Error = &api.KeyError{
+				Err:            "Self-signing key sanity check failed: " + err.Error(),
+				IsInvalidParam: true,
+			}
+			return nil
+		}
+
+		byPurpose[gomatrixserverlib.CrossSigningKeyPurposeSelfSigning] = req.SelfSigningKey
+		for _, key := range req.SelfSigningKey.Keys { // iterates once, see sanityCheckKey
+			toStore[gomatrixserverlib.CrossSigningKeyPurposeSelfSigning] = key
+		}
+	}
+
+	if len(req.UserSigningKey.Keys) > 0 {
+		if err := sanityCheckKey(req.UserSigningKey, req.UserID, gomatrixserverlib.CrossSigningKeyPurposeUserSigning); err != nil {
+			res.Error = &api.KeyError{
+				Err:            "User-signing key sanity check failed: " + err.Error(),
+				IsInvalidParam: true,
+			}
+			return nil
+		}
+
+		byPurpose[gomatrixserverlib.CrossSigningKeyPurposeUserSigning] = req.UserSigningKey
+		for _, key := range req.UserSigningKey.Keys { // iterates once, see sanityCheckKey
+			toStore[gomatrixserverlib.CrossSigningKeyPurposeUserSigning] = key
+		}
+	}
+
+	// If there's nothing to do then stop here.
+	if len(toStore) == 0 {
+		res.Error = &api.KeyError{
+			Err:            "No keys were supplied in the request",
+			IsMissingParam: true,
+		}
+		return nil
+	}
+
+	// We can't have a self-signing or user-signing key without a master
+	// key, so make sure we have one of those. We will also only actually do
+	// something if any of the specified keys in the request are different
+	// to what we've got in the database, to avoid generating key change
+	// notifications unnecessarily.
+	existingKeys, err := a.KeyDatabase.CrossSigningKeysDataForUser(ctx, req.UserID)
+	if err != nil {
+		res.Error = &api.KeyError{
+			Err: "Retrieving cross-signing keys from database failed: " + err.Error(),
+		}
+		return nil
+	}
+
+	// If we still can't find a master key for the user then stop the upload.
+	// This satisfies the "Fails to upload self-signing key without master key" test.
+	if !hasMasterKey {
+		if _, hasMasterKey = existingKeys[gomatrixserverlib.CrossSigningKeyPurposeMaster]; !hasMasterKey {
+			res.Error = &api.KeyError{
+				Err:            "No master key was found",
+				IsMissingParam: true,
+			}
+			return nil
+		}
+	}
+
+	// Check if anything actually changed compared to what we have in the database.
+	changed := false
+	for _, purpose := range []gomatrixserverlib.CrossSigningKeyPurpose{
+		gomatrixserverlib.CrossSigningKeyPurposeMaster,
+		gomatrixserverlib.CrossSigningKeyPurposeSelfSigning,
+		gomatrixserverlib.CrossSigningKeyPurposeUserSigning,
+	} {
+		old, gotOld := existingKeys[purpose]
+		new, gotNew := toStore[purpose]
+		if gotOld != gotNew {
+			// A new key purpose has been specified that we didn't know before,
+			// or one has been removed.
+			changed = true
+			break
+		}
+		if !bytes.Equal(old, new) {
+			// One of the existing keys for a purpose we already knew about has
+			// changed.
+			changed = true
+			break
+		}
+	}
+	if !changed {
+		return nil
+	}
+
+	// Store the keys.
+	if err := a.KeyDatabase.StoreCrossSigningKeysForUser(ctx, req.UserID, toStore); err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("a.DB.StoreCrossSigningKeysForUser: %s", err),
+		}
+		return nil
+	}
+
+	// Now upload any signatures that were included with the keys.
+	for _, key := range byPurpose {
+		var targetKeyID gomatrixserverlib.KeyID
+		for targetKey := range key.Keys { // iterates once, see sanityCheckKey
+			targetKeyID = targetKey
+		}
+		for sigUserID, forSigUserID := range key.Signatures {
+			if sigUserID != req.UserID {
+				continue
+			}
+			for sigKeyID, sigBytes := range forSigUserID {
+				if err := a.KeyDatabase.StoreCrossSigningSigsForTarget(ctx, sigUserID, sigKeyID, req.UserID, targetKeyID, sigBytes); err != nil {
+					res.Error = &api.KeyError{
+						Err: fmt.Sprintf("a.DB.StoreCrossSigningSigsForTarget: %s", err),
+					}
+					return nil
+				}
+			}
+		}
+	}
+
+	// Finally, generate a notification that we updated the keys.
+	update := api.CrossSigningKeyUpdate{
+		UserID: req.UserID,
+	}
+	if mk, ok := byPurpose[gomatrixserverlib.CrossSigningKeyPurposeMaster]; ok {
+		update.MasterKey = &mk
+	}
+	if ssk, ok := byPurpose[gomatrixserverlib.CrossSigningKeyPurposeSelfSigning]; ok {
+		update.SelfSigningKey = &ssk
+	}
+	if update.MasterKey == nil && update.SelfSigningKey == nil {
+		return nil
+	}
+	if err := a.KeyChangeProducer.ProduceSigningKeyUpdate(update); err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("a.Producer.ProduceSigningKeyUpdate: %s", err),
+		}
+		return nil
+	}
+	return nil
+}
+
+func (a *UserInternalAPI) PerformUploadDeviceSignatures(ctx context.Context, req *api.PerformUploadDeviceSignaturesRequest, res *api.PerformUploadDeviceSignaturesResponse) error {
+	// Before we do anything, we need the master and self-signing keys for this user.
+	// Then we can verify the signatures make sense.
+	queryReq := &api.QueryKeysRequest{
+		UserID:        req.UserID,
+		UserToDevices: map[string][]string{},
+	}
+	queryRes := &api.QueryKeysResponse{}
+	for userID := range req.Signatures {
+		queryReq.UserToDevices[userID] = []string{}
+	}
+	_ = a.QueryKeys(ctx, queryReq, queryRes)
+
+	selfSignatures := map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+	otherSignatures := map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+
+	// Sort signatures into two groups: one where people have signed their own
+	// keys and one where people have signed someone elses
+	for userID, forUserID := range req.Signatures {
+		for keyID, keyOrDevice := range forUserID {
+			switch key := keyOrDevice.CrossSigningBody.(type) {
+			case *gomatrixserverlib.CrossSigningKey:
+				if key.UserID == req.UserID {
+					if _, ok := selfSignatures[userID]; !ok {
+						selfSignatures[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+					}
+					selfSignatures[userID][keyID] = keyOrDevice
+				} else {
+					if _, ok := otherSignatures[userID]; !ok {
+						otherSignatures[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+					}
+					otherSignatures[userID][keyID] = keyOrDevice
+				}
+
+			case *gomatrixserverlib.DeviceKeys:
+				if key.UserID == req.UserID {
+					if _, ok := selfSignatures[userID]; !ok {
+						selfSignatures[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+					}
+					selfSignatures[userID][keyID] = keyOrDevice
+				} else {
+					if _, ok := otherSignatures[userID]; !ok {
+						otherSignatures[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+					}
+					otherSignatures[userID][keyID] = keyOrDevice
+				}
+
+			default:
+				continue
+			}
+		}
+	}
+
+	if err := a.processSelfSignatures(ctx, selfSignatures); err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("a.processSelfSignatures: %s", err),
+		}
+		return nil
+	}
+
+	if err := a.processOtherSignatures(ctx, req.UserID, queryRes, otherSignatures); err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("a.processOtherSignatures: %s", err),
+		}
+		return nil
+	}
+
+	// Finally, generate a notification that we updated the signatures.
+	for userID := range req.Signatures {
+		masterKey := queryRes.MasterKeys[userID]
+		selfSigningKey := queryRes.SelfSigningKeys[userID]
+		update := api.CrossSigningKeyUpdate{
+			UserID:         userID,
+			MasterKey:      &masterKey,
+			SelfSigningKey: &selfSigningKey,
+		}
+		if err := a.KeyChangeProducer.ProduceSigningKeyUpdate(update); err != nil {
+			res.Error = &api.KeyError{
+				Err: fmt.Sprintf("a.Producer.ProduceSigningKeyUpdate: %s", err),
+			}
+			return nil
+		}
+	}
+	return nil
+}
+
+func (a *UserInternalAPI) processSelfSignatures(
+	ctx context.Context,
+	signatures map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice,
+) error {
+	// Here we will process:
+	// * The user signing their own devices using their self-signing key
+	// * The user signing their master key using one of their devices
+
+	for targetUserID, forTargetUserID := range signatures {
+		for targetKeyID, signature := range forTargetUserID {
+			switch sig := signature.CrossSigningBody.(type) {
+			case *gomatrixserverlib.CrossSigningKey:
+				for keyID := range sig.Keys {
+					split := strings.SplitN(string(keyID), ":", 2)
+					if len(split) > 1 && gomatrixserverlib.KeyID(split[1]) == targetKeyID {
+						targetKeyID = keyID // contains the ed25519: or other scheme
+						break
+					}
+				}
+				for originUserID, forOriginUserID := range sig.Signatures {
+					for originKeyID, originSig := range forOriginUserID {
+						if err := a.KeyDatabase.StoreCrossSigningSigsForTarget(
+							ctx, originUserID, originKeyID, targetUserID, targetKeyID, originSig,
+						); err != nil {
+							return fmt.Errorf("a.DB.StoreCrossSigningKeysForTarget: %w", err)
+						}
+					}
+				}
+
+			case *gomatrixserverlib.DeviceKeys:
+				for originUserID, forOriginUserID := range sig.Signatures {
+					for originKeyID, originSig := range forOriginUserID {
+						if err := a.KeyDatabase.StoreCrossSigningSigsForTarget(
+							ctx, originUserID, originKeyID, targetUserID, targetKeyID, originSig,
+						); err != nil {
+							return fmt.Errorf("a.DB.StoreCrossSigningKeysForTarget: %w", err)
+						}
+					}
+				}
+
+			default:
+				return fmt.Errorf("unexpected type assertion")
+			}
+		}
+	}
+
+	return nil
+}
+
+func (a *UserInternalAPI) processOtherSignatures(
+	ctx context.Context, userID string, queryRes *api.QueryKeysResponse,
+	signatures map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice,
+) error {
+	// Here we will process:
+	// * A user signing someone else's master keys using their user-signing keys
+
+	for targetUserID, forTargetUserID := range signatures {
+		for _, signature := range forTargetUserID {
+			switch sig := signature.CrossSigningBody.(type) {
+			case *gomatrixserverlib.CrossSigningKey:
+				// Find the local copy of the master key. We'll use this to be
+				// sure that the supplied stanza matches the key that we think it
+				// should be.
+				masterKey, ok := queryRes.MasterKeys[targetUserID]
+				if !ok {
+					return fmt.Errorf("failed to find master key for user %q", targetUserID)
+				}
+
+				// For each key ID, write the signatures. Maybe there'll be more
+				// than one algorithm in the future so it's best not to focus on
+				// everything being ed25519:.
+				for targetKeyID, suppliedKeyData := range sig.Keys {
+					// The master key will be supplied in the request, but we should
+					// make sure that it matches what we think the master key should
+					// actually be.
+					localKeyData, lok := masterKey.Keys[targetKeyID]
+					if !lok {
+						return fmt.Errorf("uploaded master key %q for user %q doesn't match local copy", targetKeyID, targetUserID)
+					} else if !bytes.Equal(suppliedKeyData, localKeyData) {
+						return fmt.Errorf("uploaded master key %q for user %q doesn't match local copy", targetKeyID, targetUserID)
+					}
+
+					// We only care about the signatures from the uploading user, so
+					// we will ignore anything that didn't originate from them.
+					userSigs, ok := sig.Signatures[userID]
+					if !ok {
+						return fmt.Errorf("there are no signatures on master key %q from uploading user %q", targetKeyID, userID)
+					}
+
+					for originKeyID, originSig := range userSigs {
+						if err := a.KeyDatabase.StoreCrossSigningSigsForTarget(
+							ctx, userID, originKeyID, targetUserID, targetKeyID, originSig,
+						); err != nil {
+							return fmt.Errorf("a.DB.StoreCrossSigningKeysForTarget: %w", err)
+						}
+					}
+				}
+
+			default:
+				// Users should only be signing another person's master key,
+				// so if we're here, it's probably because it's actually a
+				// gomatrixserverlib.DeviceKeys, which doesn't make sense.
+			}
+		}
+	}
+
+	return nil
+}
+
+func (a *UserInternalAPI) crossSigningKeysFromDatabase(
+	ctx context.Context, req *api.QueryKeysRequest, res *api.QueryKeysResponse,
+) {
+	for targetUserID := range req.UserToDevices {
+		keys, err := a.KeyDatabase.CrossSigningKeysForUser(ctx, targetUserID)
+		if err != nil {
+			logrus.WithError(err).Errorf("Failed to get cross-signing keys for user %q", targetUserID)
+			continue
+		}
+
+		for keyType, key := range keys {
+			var keyID gomatrixserverlib.KeyID
+			for id := range key.Keys {
+				keyID = id
+				break
+			}
+
+			sigMap, err := a.KeyDatabase.CrossSigningSigsForTarget(ctx, req.UserID, targetUserID, keyID)
+			if err != nil && err != sql.ErrNoRows {
+				logrus.WithError(err).Errorf("Failed to get cross-signing signatures for user %q key %q", targetUserID, keyID)
+				continue
+			}
+
+			appendSignature := func(originUserID string, originKeyID gomatrixserverlib.KeyID, signature gomatrixserverlib.Base64Bytes) {
+				if key.Signatures == nil {
+					key.Signatures = types.CrossSigningSigMap{}
+				}
+				if _, ok := key.Signatures[originUserID]; !ok {
+					key.Signatures[originUserID] = make(map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes)
+				}
+				key.Signatures[originUserID][originKeyID] = signature
+			}
+
+			for originUserID, forOrigin := range sigMap {
+				for originKeyID, signature := range forOrigin {
+					switch {
+					case req.UserID != "" && originUserID == req.UserID:
+						// Include signatures that we created
+						appendSignature(originUserID, originKeyID, signature)
+					case originUserID == targetUserID:
+						// Include signatures that were created by the person whose key
+						// we are processing
+						appendSignature(originUserID, originKeyID, signature)
+					}
+				}
+			}
+
+			switch keyType {
+			case gomatrixserverlib.CrossSigningKeyPurposeMaster:
+				res.MasterKeys[targetUserID] = key
+
+			case gomatrixserverlib.CrossSigningKeyPurposeSelfSigning:
+				res.SelfSigningKeys[targetUserID] = key
+
+			case gomatrixserverlib.CrossSigningKeyPurposeUserSigning:
+				res.UserSigningKeys[targetUserID] = key
+			}
+		}
+	}
+}
+
+func (a *UserInternalAPI) QuerySignatures(ctx context.Context, req *api.QuerySignaturesRequest, res *api.QuerySignaturesResponse) error {
+	for targetUserID, forTargetUser := range req.TargetIDs {
+		keyMap, err := a.KeyDatabase.CrossSigningKeysForUser(ctx, targetUserID)
+		if err != nil && err != sql.ErrNoRows {
+			res.Error = &api.KeyError{
+				Err: fmt.Sprintf("a.DB.CrossSigningKeysForUser: %s", err),
+			}
+			continue
+		}
+
+		for targetPurpose, targetKey := range keyMap {
+			switch targetPurpose {
+			case gomatrixserverlib.CrossSigningKeyPurposeMaster:
+				if res.MasterKeys == nil {
+					res.MasterKeys = map[string]gomatrixserverlib.CrossSigningKey{}
+				}
+				res.MasterKeys[targetUserID] = targetKey
+
+			case gomatrixserverlib.CrossSigningKeyPurposeSelfSigning:
+				if res.SelfSigningKeys == nil {
+					res.SelfSigningKeys = map[string]gomatrixserverlib.CrossSigningKey{}
+				}
+				res.SelfSigningKeys[targetUserID] = targetKey
+
+			case gomatrixserverlib.CrossSigningKeyPurposeUserSigning:
+				if res.UserSigningKeys == nil {
+					res.UserSigningKeys = map[string]gomatrixserverlib.CrossSigningKey{}
+				}
+				res.UserSigningKeys[targetUserID] = targetKey
+			}
+		}
+
+		for _, targetKeyID := range forTargetUser {
+			// Get own signatures only.
+			sigMap, err := a.KeyDatabase.CrossSigningSigsForTarget(ctx, targetUserID, targetUserID, targetKeyID)
+			if err != nil && err != sql.ErrNoRows {
+				res.Error = &api.KeyError{
+					Err: fmt.Sprintf("a.DB.CrossSigningSigsForTarget: %s", err),
+				}
+				return nil
+			}
+
+			for sourceUserID, forSourceUser := range sigMap {
+				for sourceKeyID, sourceSig := range forSourceUser {
+					if res.Signatures == nil {
+						res.Signatures = map[string]map[gomatrixserverlib.KeyID]types.CrossSigningSigMap{}
+					}
+					if _, ok := res.Signatures[targetUserID]; !ok {
+						res.Signatures[targetUserID] = map[gomatrixserverlib.KeyID]types.CrossSigningSigMap{}
+					}
+					if _, ok := res.Signatures[targetUserID][targetKeyID]; !ok {
+						res.Signatures[targetUserID][targetKeyID] = types.CrossSigningSigMap{}
+					}
+					if _, ok := res.Signatures[targetUserID][targetKeyID][sourceUserID]; !ok {
+						res.Signatures[targetUserID][targetKeyID][sourceUserID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+					}
+					res.Signatures[targetUserID][targetKeyID][sourceUserID][sourceKeyID] = sourceSig
+				}
+			}
+		}
+	}
+	return nil
+}
diff --git a/userapi/internal/device_list_update.go b/userapi/internal/device_list_update.go
new file mode 100644
index 00000000..3b4dcf98
--- /dev/null
+++ b/userapi/internal/device_list_update.go
@@ -0,0 +1,579 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import (
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"hash/fnv"
+	"net"
+	"sync"
+	"time"
+
+	rsapi "github.com/matrix-org/dendrite/roomserver/api"
+
+	"github.com/matrix-org/gomatrix"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/sirupsen/logrus"
+
+	fedsenderapi "github.com/matrix-org/dendrite/federationapi/api"
+	"github.com/matrix-org/dendrite/setup/process"
+	"github.com/matrix-org/dendrite/userapi/api"
+)
+
+var (
+	deviceListUpdateCount = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: "dendrite",
+			Subsystem: "keyserver",
+			Name:      "device_list_update",
+			Help:      "Number of times we have attempted to update device lists from this server",
+		},
+		[]string{"server"},
+	)
+)
+
+const requestTimeout = time.Second * 30
+
+func init() {
+	prometheus.MustRegister(
+		deviceListUpdateCount,
+	)
+}
+
+// DeviceListUpdater handles device list updates from remote servers.
+//
+// In the case where we have the prev_id for an update, the updater just stores the update (after acquiring a per-user lock).
+// In the case where we do not have the prev_id for an update, the updater marks the user_id as stale and notifies
+// a worker to get the latest device list for this user. Note: stream IDs are scoped per user so missing a prev_id
+// for a (user, device) does not mean that DEVICE is outdated as the previous ID could be for a different device:
+// we have to invalidate all devices for that user. Once the list has been fetched, the per-user lock is acquired and the
+// updater stores the latest list along with the latest stream ID.
+//
+// On startup, the updater spins up N workers which are responsible for querying device keys from remote servers.
+// Workers are scoped by homeserver domain, with one worker responsible for many domains, determined by hashing
+// mod N the server name. Work is sent via a channel which just serves to "poke" the worker as the data is retrieved
+// from the database (which allows us to batch requests to the same server). This has a number of desirable properties:
+//   - We guarantee only 1 in-flight /keys/query request per server at any time as there is exactly 1 worker responsible
+//     for that domain.
+//   - We don't have unbounded growth in proportion to the number of servers (this is more important in a P2P world where
+//     we have many many servers)
+//   - We can adjust concurrency (at the cost of memory usage) by tuning N, to accommodate mobile devices vs servers.
+//
+// The downsides are that:
+//   - Query requests can get queued behind other servers if they hash to the same worker, even if there are other free
+//     workers elsewhere. Whilst suboptimal, provided we cap how long a single request can last (e.g using context timeouts)
+//     we guarantee we will get around to it. Also, more users on a given server does not increase the number of requests
+//     (as /keys/query allows multiple users to be specified) so being stuck behind matrix.org won't materially be any worse
+//     than being stuck behind foo.bar
+//
+// In the event that the query fails, a lock is acquired and the server name along with the time to wait before retrying is
+// set in a map. A restarter goroutine periodically probes this map and injects servers which are ready to be retried.
+type DeviceListUpdater struct {
+	process *process.ProcessContext
+	// A map from user_id to a mutex. Used when we are missing prev IDs so we don't make more than 1
+	// request to the remote server and race.
+	// TODO: Put in an LRU cache to bound growth
+	userIDToMutex map[string]*sync.Mutex
+	mu            *sync.Mutex // protects UserIDToMutex
+
+	db          DeviceListUpdaterDatabase
+	api         DeviceListUpdaterAPI
+	producer    KeyChangeProducer
+	fedClient   fedsenderapi.KeyserverFederationAPI
+	workerChans []chan gomatrixserverlib.ServerName
+	thisServer  gomatrixserverlib.ServerName
+
+	// When device lists are stale for a user, they get inserted into this map with a channel which `Update` will
+	// block on or timeout via a select.
+	userIDToChan   map[string]chan bool
+	userIDToChanMu *sync.Mutex
+	rsAPI          rsapi.KeyserverRoomserverAPI
+}
+
+// DeviceListUpdaterDatabase is the subset of functionality from storage.Database required for the updater.
+// Useful for testing.
+type DeviceListUpdaterDatabase interface {
+	// StaleDeviceLists returns a list of user IDs ending with the domains provided who have stale device lists.
+	// If no domains are given, all user IDs with stale device lists are returned.
+	StaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error)
+
+	// MarkDeviceListStale sets the stale bit for this user to isStale.
+	MarkDeviceListStale(ctx context.Context, userID string, isStale bool) error
+
+	// StoreRemoteDeviceKeys persists the given keys. Keys with the same user ID and device ID will be replaced. An empty KeyJSON removes the key
+	// for this (user, device). Does not modify the stream ID for keys. User IDs in `clearUserIDs` will have all their device keys deleted prior
+	// to insertion - use this when you have a complete snapshot of a user's keys in order to track device deletions correctly.
+	StoreRemoteDeviceKeys(ctx context.Context, keys []api.DeviceMessage, clearUserIDs []string) error
+
+	// PrevIDsExists returns true if all prev IDs exist for this user.
+	PrevIDsExists(ctx context.Context, userID string, prevIDs []int64) (bool, error)
+
+	// DeviceKeysJSON populates the KeyJSON for the given keys. If any proided `keys` have a `KeyJSON` or `StreamID` already then it will be replaced.
+	DeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error
+
+	DeleteStaleDeviceLists(ctx context.Context, userIDs []string) error
+}
+
+type DeviceListUpdaterAPI interface {
+	PerformUploadDeviceKeys(ctx context.Context, req *api.PerformUploadDeviceKeysRequest, res *api.PerformUploadDeviceKeysResponse) error
+}
+
+// KeyChangeProducer is the interface for producers.KeyChange useful for testing.
+type KeyChangeProducer interface {
+	ProduceKeyChanges(keys []api.DeviceMessage) error
+}
+
+// NewDeviceListUpdater creates a new updater which fetches fresh device lists when they go stale.
+func NewDeviceListUpdater(
+	process *process.ProcessContext, db DeviceListUpdaterDatabase,
+	api DeviceListUpdaterAPI, producer KeyChangeProducer,
+	fedClient fedsenderapi.KeyserverFederationAPI, numWorkers int,
+	rsAPI rsapi.KeyserverRoomserverAPI, thisServer gomatrixserverlib.ServerName,
+) *DeviceListUpdater {
+	return &DeviceListUpdater{
+		process:        process,
+		userIDToMutex:  make(map[string]*sync.Mutex),
+		mu:             &sync.Mutex{},
+		db:             db,
+		api:            api,
+		producer:       producer,
+		fedClient:      fedClient,
+		thisServer:     thisServer,
+		workerChans:    make([]chan gomatrixserverlib.ServerName, numWorkers),
+		userIDToChan:   make(map[string]chan bool),
+		userIDToChanMu: &sync.Mutex{},
+		rsAPI:          rsAPI,
+	}
+}
+
+// Start the device list updater, which will try to refresh any stale device lists.
+func (u *DeviceListUpdater) Start() error {
+	for i := 0; i < len(u.workerChans); i++ {
+		// Allocate a small buffer per channel.
+		// If the buffer limit is reached, backpressure will cause the processing of EDUs
+		// to stop (in this transaction) until key requests can be made.
+		ch := make(chan gomatrixserverlib.ServerName, 10)
+		u.workerChans[i] = ch
+		go u.worker(ch)
+	}
+
+	staleLists, err := u.db.StaleDeviceLists(u.process.Context(), []gomatrixserverlib.ServerName{})
+	if err != nil {
+		return err
+	}
+	offset, step := time.Second*10, time.Second
+	if max := len(staleLists); max > 120 {
+		step = (time.Second * 120) / time.Duration(max)
+	}
+	for _, userID := range staleLists {
+		userID := userID // otherwise we are only sending the last entry
+		time.AfterFunc(offset, func() {
+			u.notifyWorkers(userID)
+		})
+		offset += step
+	}
+	return nil
+}
+
+// CleanUp removes stale device entries for users we don't share a room with anymore
+func (u *DeviceListUpdater) CleanUp() error {
+	staleUsers, err := u.db.StaleDeviceLists(u.process.Context(), []gomatrixserverlib.ServerName{})
+	if err != nil {
+		return err
+	}
+
+	res := rsapi.QueryLeftUsersResponse{}
+	if err = u.rsAPI.QueryLeftUsers(u.process.Context(), &rsapi.QueryLeftUsersRequest{StaleDeviceListUsers: staleUsers}, &res); err != nil {
+		return err
+	}
+
+	if len(res.LeftUsers) == 0 {
+		return nil
+	}
+	logrus.Debugf("Deleting %d stale device list entries", len(res.LeftUsers))
+	return u.db.DeleteStaleDeviceLists(u.process.Context(), res.LeftUsers)
+}
+
+func (u *DeviceListUpdater) mutex(userID string) *sync.Mutex {
+	u.mu.Lock()
+	defer u.mu.Unlock()
+	if u.userIDToMutex[userID] == nil {
+		u.userIDToMutex[userID] = &sync.Mutex{}
+	}
+	return u.userIDToMutex[userID]
+}
+
+// ManualUpdate invalidates the device list for the given user and fetches the latest and tracks it.
+// Blocks until the device list is synced or the timeout is reached.
+func (u *DeviceListUpdater) ManualUpdate(ctx context.Context, serverName gomatrixserverlib.ServerName, userID string) error {
+	mu := u.mutex(userID)
+	mu.Lock()
+	err := u.db.MarkDeviceListStale(ctx, userID, true)
+	mu.Unlock()
+	if err != nil {
+		return fmt.Errorf("ManualUpdate: failed to mark device list for %s as stale: %w", userID, err)
+	}
+	u.notifyWorkers(userID)
+	return nil
+}
+
+// Update blocks until the update has been stored in the database. It blocks primarily for satisfying sytest,
+// which assumes when /send 200 OKs that the device lists have been updated.
+func (u *DeviceListUpdater) Update(ctx context.Context, event gomatrixserverlib.DeviceListUpdateEvent) error {
+	isDeviceListStale, err := u.update(ctx, event)
+	if err != nil {
+		return err
+	}
+	if isDeviceListStale {
+		// poke workers to handle stale device lists
+		u.notifyWorkers(event.UserID)
+	}
+	return nil
+}
+
+func (u *DeviceListUpdater) update(ctx context.Context, event gomatrixserverlib.DeviceListUpdateEvent) (bool, error) {
+	mu := u.mutex(event.UserID)
+	mu.Lock()
+	defer mu.Unlock()
+	// check if we have the prev IDs
+	exists, err := u.db.PrevIDsExists(ctx, event.UserID, event.PrevID)
+	if err != nil {
+		return false, fmt.Errorf("failed to check prev IDs exist for %s (%s): %w", event.UserID, event.DeviceID, err)
+	}
+	// if this is the first time we're hearing about this user, sync the device list manually.
+	if len(event.PrevID) == 0 {
+		exists = false
+	}
+	util.GetLogger(ctx).WithFields(logrus.Fields{
+		"prev_ids_exist": exists,
+		"user_id":        event.UserID,
+		"device_id":      event.DeviceID,
+		"stream_id":      event.StreamID,
+		"prev_ids":       event.PrevID,
+		"display_name":   event.DeviceDisplayName,
+		"deleted":        event.Deleted,
+	}).Trace("DeviceListUpdater.Update")
+
+	// if we haven't missed anything update the database and notify users
+	if exists || event.Deleted {
+		k := event.Keys
+		if event.Deleted {
+			k = nil
+		}
+		keys := []api.DeviceMessage{
+			{
+				Type: api.TypeDeviceKeyUpdate,
+				DeviceKeys: &api.DeviceKeys{
+					DeviceID:    event.DeviceID,
+					DisplayName: event.DeviceDisplayName,
+					KeyJSON:     k,
+					UserID:      event.UserID,
+				},
+				StreamID: event.StreamID,
+			},
+		}
+
+		// DeviceKeysJSON will side-effect modify this, so it needs
+		// to be a copy, not sharing any pointers with the above.
+		deviceKeysCopy := *keys[0].DeviceKeys
+		deviceKeysCopy.KeyJSON = nil
+		existingKeys := []api.DeviceMessage{
+			{
+				Type:       keys[0].Type,
+				DeviceKeys: &deviceKeysCopy,
+				StreamID:   keys[0].StreamID,
+			},
+		}
+
+		// fetch what keys we had already and only emit changes
+		if err = u.db.DeviceKeysJSON(ctx, existingKeys); err != nil {
+			// non-fatal, log and continue
+			util.GetLogger(ctx).WithError(err).WithField("user_id", event.UserID).Errorf(
+				"failed to query device keys json for calculating diffs",
+			)
+		}
+
+		err = u.db.StoreRemoteDeviceKeys(ctx, keys, nil)
+		if err != nil {
+			return false, fmt.Errorf("failed to store remote device keys for %s (%s): %w", event.UserID, event.DeviceID, err)
+		}
+
+		if err = emitDeviceKeyChanges(u.producer, existingKeys, keys, false); err != nil {
+			return false, fmt.Errorf("failed to produce device key changes for %s (%s): %w", event.UserID, event.DeviceID, err)
+		}
+		return false, nil
+	}
+
+	err = u.db.MarkDeviceListStale(ctx, event.UserID, true)
+	if err != nil {
+		return false, fmt.Errorf("failed to mark device list for %s as stale: %w", event.UserID, err)
+	}
+
+	return true, nil
+}
+
+func (u *DeviceListUpdater) notifyWorkers(userID string) {
+	_, remoteServer, err := gomatrixserverlib.SplitID('@', userID)
+	if err != nil {
+		return
+	}
+	hash := fnv.New32a()
+	_, _ = hash.Write([]byte(remoteServer))
+	index := int(int64(hash.Sum32()) % int64(len(u.workerChans)))
+
+	ch := u.assignChannel(userID)
+	u.workerChans[index] <- remoteServer
+	select {
+	case <-ch:
+	case <-time.After(10 * time.Second):
+		// we don't return an error in this case as it's not a failure condition.
+		// we mainly block for the benefit of sytest anyway
+	}
+}
+
+func (u *DeviceListUpdater) assignChannel(userID string) chan bool {
+	u.userIDToChanMu.Lock()
+	defer u.userIDToChanMu.Unlock()
+	if ch, ok := u.userIDToChan[userID]; ok {
+		return ch
+	}
+	ch := make(chan bool)
+	u.userIDToChan[userID] = ch
+	return ch
+}
+
+func (u *DeviceListUpdater) clearChannel(userID string) {
+	u.userIDToChanMu.Lock()
+	defer u.userIDToChanMu.Unlock()
+	if ch, ok := u.userIDToChan[userID]; ok {
+		close(ch)
+		delete(u.userIDToChan, userID)
+	}
+}
+
+func (u *DeviceListUpdater) worker(ch chan gomatrixserverlib.ServerName) {
+	retries := make(map[gomatrixserverlib.ServerName]time.Time)
+	retriesMu := &sync.Mutex{}
+	// restarter goroutine which will inject failed servers into ch when it is time
+	go func() {
+		var serversToRetry []gomatrixserverlib.ServerName
+		for {
+			serversToRetry = serversToRetry[:0] // reuse memory
+			time.Sleep(time.Second)
+			retriesMu.Lock()
+			now := time.Now()
+			for srv, retryAt := range retries {
+				if now.After(retryAt) {
+					serversToRetry = append(serversToRetry, srv)
+				}
+			}
+			for _, srv := range serversToRetry {
+				delete(retries, srv)
+			}
+			retriesMu.Unlock()
+			for _, srv := range serversToRetry {
+				ch <- srv
+			}
+		}
+	}()
+	for serverName := range ch {
+		retriesMu.Lock()
+		_, exists := retries[serverName]
+		retriesMu.Unlock()
+		if exists {
+			// Don't retry a server that we're already waiting for.
+			continue
+		}
+		waitTime, shouldRetry := u.processServer(serverName)
+		if shouldRetry {
+			retriesMu.Lock()
+			if _, exists = retries[serverName]; !exists {
+				retries[serverName] = time.Now().Add(waitTime)
+			}
+			retriesMu.Unlock()
+		}
+	}
+}
+
+func (u *DeviceListUpdater) processServer(serverName gomatrixserverlib.ServerName) (time.Duration, bool) {
+	ctx := u.process.Context()
+	logger := util.GetLogger(ctx).WithField("server_name", serverName)
+	deviceListUpdateCount.WithLabelValues(string(serverName)).Inc()
+
+	waitTime := defaultWaitTime // How long should we wait to try again?
+	successCount := 0           // How many user requests failed?
+
+	userIDs, err := u.db.StaleDeviceLists(ctx, []gomatrixserverlib.ServerName{serverName})
+	if err != nil {
+		logger.WithError(err).Error("Failed to load stale device lists")
+		return waitTime, true
+	}
+
+	defer func() {
+		for _, userID := range userIDs {
+			// always clear the channel to unblock Update calls regardless of success/failure
+			u.clearChannel(userID)
+		}
+	}()
+
+	for _, userID := range userIDs {
+		userWait, err := u.processServerUser(ctx, serverName, userID)
+		if err != nil {
+			if userWait > waitTime {
+				waitTime = userWait
+			}
+			break
+		}
+		successCount++
+	}
+
+	allUsersSucceeded := successCount == len(userIDs)
+	if !allUsersSucceeded {
+		logger.WithFields(logrus.Fields{
+			"total":     len(userIDs),
+			"succeeded": successCount,
+			"failed":    len(userIDs) - successCount,
+			"wait_time": waitTime,
+		}).Debug("Failed to query device keys for some users")
+	}
+	return waitTime, !allUsersSucceeded
+}
+
+func (u *DeviceListUpdater) processServerUser(ctx context.Context, serverName gomatrixserverlib.ServerName, userID string) (time.Duration, error) {
+	ctx, cancel := context.WithTimeout(ctx, requestTimeout)
+	defer cancel()
+	logger := util.GetLogger(ctx).WithFields(logrus.Fields{
+		"server_name": serverName,
+		"user_id":     userID,
+	})
+	res, err := u.fedClient.GetUserDevices(ctx, u.thisServer, serverName, userID)
+	if err != nil {
+		if errors.Is(err, context.DeadlineExceeded) {
+			return time.Minute * 10, err
+		}
+		switch e := err.(type) {
+		case *json.UnmarshalTypeError, *json.SyntaxError:
+			logger.WithError(err).Debugf("Device list update for %q contained invalid JSON", userID)
+			return defaultWaitTime, nil
+		case *fedsenderapi.FederationClientError:
+			if e.RetryAfter > 0 {
+				return e.RetryAfter, err
+			} else if e.Blacklisted {
+				return time.Hour * 8, err
+			}
+		case net.Error:
+			// Use the default waitTime, if it's a timeout.
+			// It probably doesn't make sense to try further users.
+			if !e.Timeout() {
+				logger.WithError(e).Debug("GetUserDevices returned net.Error")
+				return time.Minute * 10, err
+			}
+		case gomatrix.HTTPError:
+			// The remote server returned an error, give it some time to recover.
+			// This is to avoid spamming remote servers, which may not be Matrix servers anymore.
+			if e.Code >= 300 {
+				logger.WithError(e).Debug("GetUserDevices returned gomatrix.HTTPError")
+				return hourWaitTime, err
+			}
+		default:
+			// Something else failed
+			logger.WithError(err).Debugf("GetUserDevices returned unknown error type: %T", err)
+			return time.Minute * 10, err
+		}
+	}
+	if res.UserID != userID {
+		logger.WithError(err).Debugf("User ID %q in device list update response doesn't match expected %q", res.UserID, userID)
+		return defaultWaitTime, nil
+	}
+	if res.MasterKey != nil || res.SelfSigningKey != nil {
+		uploadReq := &api.PerformUploadDeviceKeysRequest{
+			UserID: userID,
+		}
+		uploadRes := &api.PerformUploadDeviceKeysResponse{}
+		if res.MasterKey != nil {
+			if err = sanityCheckKey(*res.MasterKey, userID, gomatrixserverlib.CrossSigningKeyPurposeMaster); err == nil {
+				uploadReq.MasterKey = *res.MasterKey
+			}
+		}
+		if res.SelfSigningKey != nil {
+			if err = sanityCheckKey(*res.SelfSigningKey, userID, gomatrixserverlib.CrossSigningKeyPurposeSelfSigning); err == nil {
+				uploadReq.SelfSigningKey = *res.SelfSigningKey
+			}
+		}
+		_ = u.api.PerformUploadDeviceKeys(ctx, uploadReq, uploadRes)
+	}
+	err = u.updateDeviceList(&res)
+	if err != nil {
+		logger.WithError(err).Error("Fetched device list but failed to store/emit it")
+		return defaultWaitTime, err
+	}
+	return defaultWaitTime, nil
+}
+
+func (u *DeviceListUpdater) updateDeviceList(res *gomatrixserverlib.RespUserDevices) error {
+	ctx := context.Background() // we've got the keys, don't time out when persisting them to the database.
+	keys := make([]api.DeviceMessage, len(res.Devices))
+	existingKeys := make([]api.DeviceMessage, len(res.Devices))
+	for i, device := range res.Devices {
+		keyJSON, err := json.Marshal(device.Keys)
+		if err != nil {
+			util.GetLogger(ctx).WithField("keys", device.Keys).Error("failed to marshal keys, skipping device")
+			continue
+		}
+		keys[i] = api.DeviceMessage{
+			Type:     api.TypeDeviceKeyUpdate,
+			StreamID: res.StreamID,
+			DeviceKeys: &api.DeviceKeys{
+				DeviceID:    device.DeviceID,
+				DisplayName: device.DisplayName,
+				UserID:      res.UserID,
+				KeyJSON:     keyJSON,
+			},
+		}
+		existingKeys[i] = api.DeviceMessage{
+			Type: api.TypeDeviceKeyUpdate,
+			DeviceKeys: &api.DeviceKeys{
+				UserID:   res.UserID,
+				DeviceID: device.DeviceID,
+			},
+		}
+	}
+	// fetch what keys we had already and only emit changes
+	if err := u.db.DeviceKeysJSON(ctx, existingKeys); err != nil {
+		// non-fatal, log and continue
+		util.GetLogger(ctx).WithError(err).WithField("user_id", res.UserID).Errorf(
+			"failed to query device keys json for calculating diffs",
+		)
+	}
+
+	err := u.db.StoreRemoteDeviceKeys(ctx, keys, []string{res.UserID})
+	if err != nil {
+		return fmt.Errorf("failed to store remote device keys: %w", err)
+	}
+	err = u.db.MarkDeviceListStale(ctx, res.UserID, false)
+	if err != nil {
+		return fmt.Errorf("failed to mark device list as fresh: %w", err)
+	}
+	err = emitDeviceKeyChanges(u.producer, existingKeys, keys, false)
+	if err != nil {
+		return fmt.Errorf("failed to emit key changes for fresh device list: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/internal/device_list_update_default.go b/userapi/internal/device_list_update_default.go
new file mode 100644
index 00000000..7d357c95
--- /dev/null
+++ b/userapi/internal/device_list_update_default.go
@@ -0,0 +1,22 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build !vw
+
+package internal
+
+import "time"
+
+const defaultWaitTime = time.Minute
+const hourWaitTime = time.Hour
diff --git a/userapi/internal/device_list_update_sytest.go b/userapi/internal/device_list_update_sytest.go
new file mode 100644
index 00000000..1c60d2eb
--- /dev/null
+++ b/userapi/internal/device_list_update_sytest.go
@@ -0,0 +1,25 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build vw
+
+package internal
+
+import "time"
+
+// Sytest is expecting to receive a `/devices` request. The way it is implemented in Dendrite
+// results in a one-hour wait time from a previous device so the test times out. This is fine for
+// production, but makes an otherwise passing test fail.
+const defaultWaitTime = time.Second
+const hourWaitTime = time.Second
diff --git a/userapi/internal/device_list_update_test.go b/userapi/internal/device_list_update_test.go
new file mode 100644
index 00000000..868fc9be
--- /dev/null
+++ b/userapi/internal/device_list_update_test.go
@@ -0,0 +1,431 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import (
+	"context"
+	"crypto/ed25519"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"reflect"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/matrix-org/gomatrixserverlib"
+
+	roomserver "github.com/matrix-org/dendrite/roomserver/api"
+	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/dendrite/setup/process"
+	"github.com/matrix-org/dendrite/test"
+	"github.com/matrix-org/dendrite/test/testrig"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/storage"
+)
+
+var (
+	ctx = context.Background()
+)
+
+type mockKeyChangeProducer struct {
+	events []api.DeviceMessage
+}
+
+func (p *mockKeyChangeProducer) ProduceKeyChanges(keys []api.DeviceMessage) error {
+	p.events = append(p.events, keys...)
+	return nil
+}
+
+type mockDeviceListUpdaterDatabase struct {
+	staleUsers   map[string]bool
+	prevIDsExist func(string, []int64) bool
+	storedKeys   []api.DeviceMessage
+	mu           sync.Mutex // protect staleUsers
+}
+
+func (d *mockDeviceListUpdaterDatabase) DeleteStaleDeviceLists(ctx context.Context, userIDs []string) error {
+	return nil
+}
+
+// StaleDeviceLists returns a list of user IDs ending with the domains provided who have stale device lists.
+// If no domains are given, all user IDs with stale device lists are returned.
+func (d *mockDeviceListUpdaterDatabase) StaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	var result []string
+	for userID, isStale := range d.staleUsers {
+		if !isStale {
+			continue
+		}
+		_, remoteServer, err := gomatrixserverlib.SplitID('@', userID)
+		if err != nil {
+			return nil, err
+		}
+		if len(domains) == 0 {
+			result = append(result, userID)
+			continue
+		}
+		for _, d := range domains {
+			if remoteServer == d {
+				result = append(result, userID)
+				break
+			}
+		}
+	}
+	return result, nil
+}
+
+// MarkDeviceListStale sets the stale bit for this user to isStale.
+func (d *mockDeviceListUpdaterDatabase) MarkDeviceListStale(ctx context.Context, userID string, isStale bool) error {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	d.staleUsers[userID] = isStale
+	return nil
+}
+
+func (d *mockDeviceListUpdaterDatabase) isStale(userID string) bool {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+	return d.staleUsers[userID]
+}
+
+// StoreRemoteDeviceKeys persists the given keys. Keys with the same user ID and device ID will be replaced. An empty KeyJSON removes the key
+// for this (user, device). Does not modify the stream ID for keys.
+func (d *mockDeviceListUpdaterDatabase) StoreRemoteDeviceKeys(ctx context.Context, keys []api.DeviceMessage, clear []string) error {
+	d.storedKeys = append(d.storedKeys, keys...)
+	return nil
+}
+
+// PrevIDsExists returns true if all prev IDs exist for this user.
+func (d *mockDeviceListUpdaterDatabase) PrevIDsExists(ctx context.Context, userID string, prevIDs []int64) (bool, error) {
+	return d.prevIDsExist(userID, prevIDs), nil
+}
+
+func (d *mockDeviceListUpdaterDatabase) DeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error {
+	return nil
+}
+
+type mockDeviceListUpdaterAPI struct {
+}
+
+func (d *mockDeviceListUpdaterAPI) PerformUploadDeviceKeys(ctx context.Context, req *api.PerformUploadDeviceKeysRequest, res *api.PerformUploadDeviceKeysResponse) error {
+	return nil
+}
+
+type roundTripper struct {
+	fn func(*http.Request) (*http.Response, error)
+}
+
+func (t *roundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	return t.fn(req)
+}
+
+func newFedClient(tripper func(*http.Request) (*http.Response, error)) *gomatrixserverlib.FederationClient {
+	_, pkey, _ := ed25519.GenerateKey(nil)
+	fedClient := gomatrixserverlib.NewFederationClient(
+		[]*gomatrixserverlib.SigningIdentity{
+			{
+				ServerName: gomatrixserverlib.ServerName("example.test"),
+				KeyID:      gomatrixserverlib.KeyID("ed25519:test"),
+				PrivateKey: pkey,
+			},
+		},
+	)
+	fedClient.Client = *gomatrixserverlib.NewClient(
+		gomatrixserverlib.WithTransport(&roundTripper{tripper}),
+	)
+	return fedClient
+}
+
+// Test that the device keys get persisted and emitted if we have the previous IDs.
+func TestUpdateHavePrevID(t *testing.T) {
+	db := &mockDeviceListUpdaterDatabase{
+		staleUsers: make(map[string]bool),
+		prevIDsExist: func(string, []int64) bool {
+			return true
+		},
+	}
+	ap := &mockDeviceListUpdaterAPI{}
+	producer := &mockKeyChangeProducer{}
+	updater := NewDeviceListUpdater(process.NewProcessContext(), db, ap, producer, nil, 1, nil, "localhost")
+	event := gomatrixserverlib.DeviceListUpdateEvent{
+		DeviceDisplayName: "Foo Bar",
+		Deleted:           false,
+		DeviceID:          "FOO",
+		Keys:              []byte(`{"key":"value"}`),
+		PrevID:            []int64{0},
+		StreamID:          1,
+		UserID:            "@alice:localhost",
+	}
+	err := updater.Update(ctx, event)
+	if err != nil {
+		t.Fatalf("Update returned an error: %s", err)
+	}
+	want := api.DeviceMessage{
+		Type:     api.TypeDeviceKeyUpdate,
+		StreamID: event.StreamID,
+		DeviceKeys: &api.DeviceKeys{
+			DeviceID:    event.DeviceID,
+			DisplayName: event.DeviceDisplayName,
+			KeyJSON:     event.Keys,
+			UserID:      event.UserID,
+		},
+	}
+	if !reflect.DeepEqual(producer.events, []api.DeviceMessage{want}) {
+		t.Errorf("Update didn't produce correct event, got %v want %v", producer.events, want)
+	}
+	if !reflect.DeepEqual(db.storedKeys, []api.DeviceMessage{want}) {
+		t.Errorf("DB didn't store correct event, got %v want %v", db.storedKeys, want)
+	}
+	if db.isStale(event.UserID) {
+		t.Errorf("%s incorrectly marked as stale", event.UserID)
+	}
+}
+
+// Test that device keys are fetched from the remote server if we are missing prev IDs
+// and that the user's devices are marked as stale until it succeeds.
+func TestUpdateNoPrevID(t *testing.T) {
+	db := &mockDeviceListUpdaterDatabase{
+		staleUsers: make(map[string]bool),
+		prevIDsExist: func(string, []int64) bool {
+			return false
+		},
+	}
+	ap := &mockDeviceListUpdaterAPI{}
+	producer := &mockKeyChangeProducer{}
+	remoteUserID := "@alice:example.somewhere"
+	var wg sync.WaitGroup
+	wg.Add(1)
+	keyJSON := `{"user_id":"` + remoteUserID + `","device_id":"JLAFKJWSCS","algorithms":["m.olm.v1.curve25519-aes-sha2","m.megolm.v1.aes-sha2"],"keys":{"curve25519:JLAFKJWSCS":"3C5BFWi2Y8MaVvjM8M22DBmh24PmgR0nPvJOIArzgyI","ed25519:JLAFKJWSCS":"lEuiRJBit0IG6nUf5pUzWTUEsRVVe/HJkoKuEww9ULI"},"signatures":{"` + remoteUserID + `":{"ed25519:JLAFKJWSCS":"dSO80A01XiigH3uBiDVx/EjzaoycHcjq9lfQX0uWsqxl2giMIiSPR8a4d291W1ihKJL/a+myXS367WT6NAIcBA"}}}`
+	fedClient := newFedClient(func(req *http.Request) (*http.Response, error) {
+		defer wg.Done()
+		if req.URL.Path != "/_matrix/federation/v1/user/devices/"+url.PathEscape(remoteUserID) {
+			return nil, fmt.Errorf("test: invalid path: %s", req.URL.Path)
+		}
+		return &http.Response{
+			StatusCode: 200,
+			Body: io.NopCloser(strings.NewReader(`
+			{
+				"user_id": "` + remoteUserID + `",
+				"stream_id": 5,
+				"devices": [
+				  {
+					"device_id": "JLAFKJWSCS",
+					"keys": ` + keyJSON + `,
+					"device_display_name": "Mobile Phone"
+				  }
+				]
+			  }
+			`)),
+		}, nil
+	})
+	updater := NewDeviceListUpdater(process.NewProcessContext(), db, ap, producer, fedClient, 2, nil, "example.test")
+	if err := updater.Start(); err != nil {
+		t.Fatalf("failed to start updater: %s", err)
+	}
+	event := gomatrixserverlib.DeviceListUpdateEvent{
+		DeviceDisplayName: "Mobile Phone",
+		Deleted:           false,
+		DeviceID:          "another_device_id",
+		Keys:              []byte(`{"key":"value"}`),
+		PrevID:            []int64{3},
+		StreamID:          4,
+		UserID:            remoteUserID,
+	}
+	err := updater.Update(ctx, event)
+
+	if err != nil {
+		t.Fatalf("Update returned an error: %s", err)
+	}
+	t.Log("waiting for /users/devices to be called...")
+	wg.Wait()
+	// wait a bit for db to be updated...
+	time.Sleep(100 * time.Millisecond)
+	want := api.DeviceMessage{
+		Type:     api.TypeDeviceKeyUpdate,
+		StreamID: 5,
+		DeviceKeys: &api.DeviceKeys{
+			DeviceID:    "JLAFKJWSCS",
+			DisplayName: "Mobile Phone",
+			UserID:      remoteUserID,
+			KeyJSON:     []byte(keyJSON),
+		},
+	}
+	// Now we should have a fresh list and the keys and emitted something
+	if db.isStale(event.UserID) {
+		t.Errorf("%s still marked as stale", event.UserID)
+	}
+	if !reflect.DeepEqual(producer.events, []api.DeviceMessage{want}) {
+		t.Logf("len got %d len want %d", len(producer.events[0].KeyJSON), len(want.KeyJSON))
+		t.Errorf("Update didn't produce correct event, got %v want %v", producer.events, want)
+	}
+	if !reflect.DeepEqual(db.storedKeys, []api.DeviceMessage{want}) {
+		t.Errorf("DB didn't store correct event, got %v want %v", db.storedKeys, want)
+	}
+
+}
+
+// Test that if we make N calls to ManualUpdate for the same user, we only do it once, assuming the
+// update is still ongoing.
+func TestDebounce(t *testing.T) {
+	t.Skipf("panic on closed channel on GHA")
+	db := &mockDeviceListUpdaterDatabase{
+		staleUsers: make(map[string]bool),
+		prevIDsExist: func(string, []int64) bool {
+			return true
+		},
+	}
+	ap := &mockDeviceListUpdaterAPI{}
+	producer := &mockKeyChangeProducer{}
+	fedCh := make(chan *http.Response, 1)
+	srv := gomatrixserverlib.ServerName("example.com")
+	userID := "@alice:example.com"
+	keyJSON := `{"user_id":"` + userID + `","device_id":"JLAFKJWSCS","algorithms":["m.olm.v1.curve25519-aes-sha2","m.megolm.v1.aes-sha2"],"keys":{"curve25519:JLAFKJWSCS":"3C5BFWi2Y8MaVvjM8M22DBmh24PmgR0nPvJOIArzgyI","ed25519:JLAFKJWSCS":"lEuiRJBit0IG6nUf5pUzWTUEsRVVe/HJkoKuEww9ULI"},"signatures":{"` + userID + `":{"ed25519:JLAFKJWSCS":"dSO80A01XiigH3uBiDVx/EjzaoycHcjq9lfQX0uWsqxl2giMIiSPR8a4d291W1ihKJL/a+myXS367WT6NAIcBA"}}}`
+	incomingFedReq := make(chan struct{})
+	fedClient := newFedClient(func(req *http.Request) (*http.Response, error) {
+		if req.URL.Path != "/_matrix/federation/v1/user/devices/"+url.PathEscape(userID) {
+			return nil, fmt.Errorf("test: invalid path: %s", req.URL.Path)
+		}
+		close(incomingFedReq)
+		return <-fedCh, nil
+	})
+	updater := NewDeviceListUpdater(process.NewProcessContext(), db, ap, producer, fedClient, 1, nil, "localhost")
+	if err := updater.Start(); err != nil {
+		t.Fatalf("failed to start updater: %s", err)
+	}
+
+	// hit this 5 times
+	var wg sync.WaitGroup
+	wg.Add(5)
+	for i := 0; i < 5; i++ {
+		go func() {
+			defer wg.Done()
+			if err := updater.ManualUpdate(context.Background(), srv, userID); err != nil {
+				t.Errorf("ManualUpdate: %s", err)
+			}
+		}()
+	}
+
+	// wait until the updater hits federation
+	select {
+	case <-incomingFedReq:
+	case <-time.After(time.Second):
+		t.Fatalf("timed out waiting for updater to hit federation")
+	}
+
+	// user should be marked as stale
+	if !db.isStale(userID) {
+		t.Errorf("user %s not marked as stale", userID)
+	}
+	// now send the response over federation
+	fedCh <- &http.Response{
+		StatusCode: 200,
+		Body: io.NopCloser(strings.NewReader(`
+		{
+			"user_id": "` + userID + `",
+			"stream_id": 5,
+			"devices": [
+			  {
+				"device_id": "JLAFKJWSCS",
+				"keys": ` + keyJSON + `,
+				"device_display_name": "Mobile Phone"
+			  }
+			]
+		  }
+		`)),
+	}
+	close(fedCh)
+	// wait until all 5 ManualUpdates return. If we hit federation again we won't send a response
+	// and should panic with read on a closed channel
+	wg.Wait()
+
+	// user is no longer stale now
+	if db.isStale(userID) {
+		t.Errorf("user %s is marked as stale", userID)
+	}
+}
+
+func mustCreateKeyserverDB(t *testing.T, dbType test.DBType) (storage.KeyDatabase, func()) {
+	t.Helper()
+
+	base, _, _ := testrig.Base(nil)
+	connStr, clearDB := test.PrepareDBConnectionString(t, dbType)
+	db, err := storage.NewKeyDatabase(base, &config.DatabaseOptions{ConnectionString: config.DataSource(connStr)})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	return db, clearDB
+}
+
+type mockKeyserverRoomserverAPI struct {
+	leftUsers []string
+}
+
+func (m *mockKeyserverRoomserverAPI) QueryLeftUsers(ctx context.Context, req *roomserver.QueryLeftUsersRequest, res *roomserver.QueryLeftUsersResponse) error {
+	res.LeftUsers = m.leftUsers
+	return nil
+}
+
+func TestDeviceListUpdater_CleanUp(t *testing.T) {
+	processCtx := process.NewProcessContext()
+
+	alice := test.NewUser(t)
+	bob := test.NewUser(t)
+
+	// Bob is not joined to any of our rooms
+	rsAPI := &mockKeyserverRoomserverAPI{leftUsers: []string{bob.ID}}
+
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		db, clearDB := mustCreateKeyserverDB(t, dbType)
+		defer clearDB()
+
+		// This should not get deleted
+		if err := db.MarkDeviceListStale(processCtx.Context(), alice.ID, true); err != nil {
+			t.Error(err)
+		}
+
+		// this one should get deleted
+		if err := db.MarkDeviceListStale(processCtx.Context(), bob.ID, true); err != nil {
+			t.Error(err)
+		}
+
+		updater := NewDeviceListUpdater(processCtx, db, nil,
+			nil, nil,
+			0, rsAPI, "test")
+		if err := updater.CleanUp(); err != nil {
+			t.Error(err)
+		}
+
+		// check that we still have Alice in our stale list
+		staleUsers, err := db.StaleDeviceLists(ctx, []gomatrixserverlib.ServerName{"test"})
+		if err != nil {
+			t.Error(err)
+		}
+
+		// There should only be Alice
+		wantCount := 1
+		if count := len(staleUsers); count != wantCount {
+			t.Fatalf("expected there to be %d stale device lists, got %d", wantCount, count)
+		}
+
+		if staleUsers[0] != alice.ID {
+			t.Fatalf("unexpected stale device list user: %s, want %s", staleUsers[0], alice.ID)
+		}
+	})
+}
diff --git a/userapi/internal/key_api.go b/userapi/internal/key_api.go
new file mode 100644
index 00000000..be816fe5
--- /dev/null
+++ b/userapi/internal/key_api.go
@@ -0,0 +1,798 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package internal
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"sync"
+	"time"
+
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+	"github.com/sirupsen/logrus"
+	"github.com/tidwall/gjson"
+	"github.com/tidwall/sjson"
+
+	"github.com/matrix-org/dendrite/userapi/api"
+)
+
+func (a *UserInternalAPI) QueryKeyChanges(ctx context.Context, req *api.QueryKeyChangesRequest, res *api.QueryKeyChangesResponse) error {
+	userIDs, latest, err := a.KeyDatabase.KeyChanges(ctx, req.Offset, req.ToOffset)
+	if err != nil {
+		res.Error = &api.KeyError{
+			Err: err.Error(),
+		}
+		return nil
+	}
+	res.Offset = latest
+	res.UserIDs = userIDs
+	return nil
+}
+
+func (a *UserInternalAPI) PerformUploadKeys(ctx context.Context, req *api.PerformUploadKeysRequest, res *api.PerformUploadKeysResponse) error {
+	res.KeyErrors = make(map[string]map[string]*api.KeyError)
+	if len(req.DeviceKeys) > 0 {
+		a.uploadLocalDeviceKeys(ctx, req, res)
+	}
+	if len(req.OneTimeKeys) > 0 {
+		a.uploadOneTimeKeys(ctx, req, res)
+	}
+	otks, err := a.KeyDatabase.OneTimeKeysCount(ctx, req.UserID, req.DeviceID)
+	if err != nil {
+		return err
+	}
+	res.OneTimeKeyCounts = []api.OneTimeKeysCount{*otks}
+	return nil
+}
+
+func (a *UserInternalAPI) PerformClaimKeys(ctx context.Context, req *api.PerformClaimKeysRequest, res *api.PerformClaimKeysResponse) error {
+	res.OneTimeKeys = make(map[string]map[string]map[string]json.RawMessage)
+	res.Failures = make(map[string]interface{})
+	// wrap request map in a top-level by-domain map
+	domainToDeviceKeys := make(map[string]map[string]map[string]string)
+	for userID, val := range req.OneTimeKeys {
+		_, serverName, err := gomatrixserverlib.SplitID('@', userID)
+		if err != nil {
+			continue // ignore invalid users
+		}
+		nested, ok := domainToDeviceKeys[string(serverName)]
+		if !ok {
+			nested = make(map[string]map[string]string)
+		}
+		nested[userID] = val
+		domainToDeviceKeys[string(serverName)] = nested
+	}
+	for domain, local := range domainToDeviceKeys {
+		if !a.Config.Matrix.IsLocalServerName(gomatrixserverlib.ServerName(domain)) {
+			continue
+		}
+		// claim local keys
+		keys, err := a.KeyDatabase.ClaimKeys(ctx, local)
+		if err != nil {
+			res.Error = &api.KeyError{
+				Err: fmt.Sprintf("failed to ClaimKeys locally: %s", err),
+			}
+		}
+		util.GetLogger(ctx).WithField("keys_claimed", len(keys)).WithField("num_users", len(local)).Info("Claimed local keys")
+		for _, key := range keys {
+			_, ok := res.OneTimeKeys[key.UserID]
+			if !ok {
+				res.OneTimeKeys[key.UserID] = make(map[string]map[string]json.RawMessage)
+			}
+			_, ok = res.OneTimeKeys[key.UserID][key.DeviceID]
+			if !ok {
+				res.OneTimeKeys[key.UserID][key.DeviceID] = make(map[string]json.RawMessage)
+			}
+			for keyID, keyJSON := range key.KeyJSON {
+				res.OneTimeKeys[key.UserID][key.DeviceID][keyID] = keyJSON
+			}
+		}
+		delete(domainToDeviceKeys, domain)
+	}
+	if len(domainToDeviceKeys) > 0 {
+		a.claimRemoteKeys(ctx, req.Timeout, res, domainToDeviceKeys)
+	}
+	return nil
+}
+
+func (a *UserInternalAPI) claimRemoteKeys(
+	ctx context.Context, timeout time.Duration, res *api.PerformClaimKeysResponse, domainToDeviceKeys map[string]map[string]map[string]string,
+) {
+	var wg sync.WaitGroup // Wait for fan-out goroutines to finish
+	var mu sync.Mutex     // Protects the response struct
+	var claimed int       // Number of keys claimed in total
+	var failures int      // Number of servers we failed to ask
+
+	util.GetLogger(ctx).Infof("Claiming remote keys from %d server(s)", len(domainToDeviceKeys))
+	wg.Add(len(domainToDeviceKeys))
+
+	for d, k := range domainToDeviceKeys {
+		go func(domain string, keysToClaim map[string]map[string]string) {
+			fedCtx, cancel := context.WithTimeout(ctx, timeout)
+			defer cancel()
+			defer wg.Done()
+
+			claimKeyRes, err := a.FedClient.ClaimKeys(fedCtx, a.Config.Matrix.ServerName, gomatrixserverlib.ServerName(domain), keysToClaim)
+
+			mu.Lock()
+			defer mu.Unlock()
+
+			if err != nil {
+				util.GetLogger(ctx).WithError(err).WithField("server", domain).Error("ClaimKeys failed")
+				res.Failures[domain] = map[string]interface{}{
+					"message": err.Error(),
+				}
+				failures++
+				return
+			}
+
+			for userID, deviceIDToKeys := range claimKeyRes.OneTimeKeys {
+				res.OneTimeKeys[userID] = make(map[string]map[string]json.RawMessage)
+				for deviceID, keys := range deviceIDToKeys {
+					res.OneTimeKeys[userID][deviceID] = keys
+					claimed += len(keys)
+				}
+			}
+		}(d, k)
+	}
+
+	wg.Wait()
+	util.GetLogger(ctx).WithFields(logrus.Fields{
+		"num_keys":     claimed,
+		"num_failures": failures,
+	}).Infof("Claimed remote keys from %d server(s)", len(domainToDeviceKeys))
+}
+
+func (a *UserInternalAPI) PerformDeleteKeys(ctx context.Context, req *api.PerformDeleteKeysRequest, res *api.PerformDeleteKeysResponse) error {
+	if err := a.KeyDatabase.DeleteDeviceKeys(ctx, req.UserID, req.KeyIDs); err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("Failed to delete device keys: %s", err),
+		}
+	}
+	return nil
+}
+
+func (a *UserInternalAPI) QueryOneTimeKeys(ctx context.Context, req *api.QueryOneTimeKeysRequest, res *api.QueryOneTimeKeysResponse) error {
+	count, err := a.KeyDatabase.OneTimeKeysCount(ctx, req.UserID, req.DeviceID)
+	if err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("Failed to query OTK counts: %s", err),
+		}
+		return nil
+	}
+	res.Count = *count
+	return nil
+}
+
+func (a *UserInternalAPI) QueryDeviceMessages(ctx context.Context, req *api.QueryDeviceMessagesRequest, res *api.QueryDeviceMessagesResponse) error {
+	msgs, err := a.KeyDatabase.DeviceKeysForUser(ctx, req.UserID, nil, false)
+	if err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("failed to query DB for device keys: %s", err),
+		}
+		return nil
+	}
+	maxStreamID := int64(0)
+	// remove deleted devices
+	var result []api.DeviceMessage
+	for _, m := range msgs {
+		if m.StreamID > maxStreamID {
+			maxStreamID = m.StreamID
+		}
+		if m.KeyJSON == nil || len(m.KeyJSON) == 0 {
+			continue
+		}
+		result = append(result, m)
+	}
+	res.Devices = result
+	res.StreamID = maxStreamID
+	return nil
+}
+
+// PerformMarkAsStaleIfNeeded marks the users device list as stale, if the given deviceID is not present
+// in our database.
+func (a *UserInternalAPI) PerformMarkAsStaleIfNeeded(ctx context.Context, req *api.PerformMarkAsStaleRequest, res *struct{}) error {
+	knownDevices, err := a.KeyDatabase.DeviceKeysForUser(ctx, req.UserID, []string{}, true)
+	if err != nil {
+		return err
+	}
+	if len(knownDevices) == 0 {
+		return nil // fmt.Errorf("unknown user %s", req.UserID)
+	}
+
+	for i := range knownDevices {
+		if knownDevices[i].DeviceID == req.DeviceID {
+			return nil // we already know about this device
+		}
+	}
+
+	return a.Updater.ManualUpdate(ctx, req.Domain, req.UserID)
+}
+
+// nolint:gocyclo
+func (a *UserInternalAPI) QueryKeys(ctx context.Context, req *api.QueryKeysRequest, res *api.QueryKeysResponse) error {
+	var respMu sync.Mutex
+	res.DeviceKeys = make(map[string]map[string]json.RawMessage)
+	res.MasterKeys = make(map[string]gomatrixserverlib.CrossSigningKey)
+	res.SelfSigningKeys = make(map[string]gomatrixserverlib.CrossSigningKey)
+	res.UserSigningKeys = make(map[string]gomatrixserverlib.CrossSigningKey)
+	res.Failures = make(map[string]interface{})
+
+	// make a map from domain to device keys
+	domainToDeviceKeys := make(map[string]map[string][]string)
+	domainToCrossSigningKeys := make(map[string]map[string]struct{})
+	for userID, deviceIDs := range req.UserToDevices {
+		_, serverName, err := gomatrixserverlib.SplitID('@', userID)
+		if err != nil {
+			continue // ignore invalid users
+		}
+		domain := string(serverName)
+		// query local devices
+		if a.Config.Matrix.IsLocalServerName(serverName) {
+			deviceKeys, err := a.KeyDatabase.DeviceKeysForUser(ctx, userID, deviceIDs, false)
+			if err != nil {
+				res.Error = &api.KeyError{
+					Err: fmt.Sprintf("failed to query local device keys: %s", err),
+				}
+				return nil
+			}
+
+			// pull out display names after we have the keys so we handle wildcards correctly
+			var dids []string
+			for _, dk := range deviceKeys {
+				dids = append(dids, dk.DeviceID)
+			}
+			var queryRes api.QueryDeviceInfosResponse
+			err = a.QueryDeviceInfos(ctx, &api.QueryDeviceInfosRequest{
+				DeviceIDs: dids,
+			}, &queryRes)
+			if err != nil {
+				util.GetLogger(ctx).Warnf("Failed to QueryDeviceInfos for device IDs, display names will be missing")
+			}
+
+			if res.DeviceKeys[userID] == nil {
+				res.DeviceKeys[userID] = make(map[string]json.RawMessage)
+			}
+			for _, dk := range deviceKeys {
+				if len(dk.KeyJSON) == 0 {
+					continue // don't include blank keys
+				}
+				// inject display name if known (either locally or remotely)
+				displayName := dk.DisplayName
+				if queryRes.DeviceInfo[dk.DeviceID].DisplayName != "" {
+					displayName = queryRes.DeviceInfo[dk.DeviceID].DisplayName
+				}
+				dk.KeyJSON, _ = sjson.SetBytes(dk.KeyJSON, "unsigned", struct {
+					DisplayName string `json:"device_display_name,omitempty"`
+				}{displayName})
+				res.DeviceKeys[userID][dk.DeviceID] = dk.KeyJSON
+			}
+		} else {
+			domainToDeviceKeys[domain] = make(map[string][]string)
+			domainToDeviceKeys[domain][userID] = append(domainToDeviceKeys[domain][userID], deviceIDs...)
+		}
+		// work out if our cross-signing request for this user was
+		// satisfied, if not add them to the list of things to fetch
+		if _, ok := res.MasterKeys[userID]; !ok {
+			if _, ok := domainToCrossSigningKeys[domain]; !ok {
+				domainToCrossSigningKeys[domain] = make(map[string]struct{})
+			}
+			domainToCrossSigningKeys[domain][userID] = struct{}{}
+		}
+		if _, ok := res.SelfSigningKeys[userID]; !ok {
+			if _, ok := domainToCrossSigningKeys[domain]; !ok {
+				domainToCrossSigningKeys[domain] = make(map[string]struct{})
+			}
+			domainToCrossSigningKeys[domain][userID] = struct{}{}
+		}
+	}
+
+	// attempt to satisfy key queries from the local database first as we should get device updates pushed to us
+	domainToDeviceKeys = a.remoteKeysFromDatabase(ctx, res, &respMu, domainToDeviceKeys)
+	if len(domainToDeviceKeys) > 0 || len(domainToCrossSigningKeys) > 0 {
+		// perform key queries for remote devices
+		a.queryRemoteKeys(ctx, req.Timeout, res, domainToDeviceKeys, domainToCrossSigningKeys)
+	}
+
+	// Now that we've done the potentially expensive work of asking the federation,
+	// try filling the cross-signing keys from the database that we know about.
+	a.crossSigningKeysFromDatabase(ctx, req, res)
+
+	// Finally, append signatures that we know about
+	// TODO: This is horrible because we need to round-trip the signature from
+	// JSON, add the signatures and marshal it again, for some reason?
+
+	for targetUserID, masterKey := range res.MasterKeys {
+		if masterKey.Signatures == nil {
+			masterKey.Signatures = map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+		}
+		for targetKeyID := range masterKey.Keys {
+			sigMap, err := a.KeyDatabase.CrossSigningSigsForTarget(ctx, req.UserID, targetUserID, targetKeyID)
+			if err != nil {
+				// Stop executing the function if the context was canceled/the deadline was exceeded,
+				// as we can't continue without a valid context.
+				if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+					return nil
+				}
+				logrus.WithError(err).Errorf("a.KeyDatabase.CrossSigningSigsForTarget failed")
+				continue
+			}
+			if len(sigMap) == 0 {
+				continue
+			}
+			for sourceUserID, forSourceUser := range sigMap {
+				for sourceKeyID, sourceSig := range forSourceUser {
+					if _, ok := masterKey.Signatures[sourceUserID]; !ok {
+						masterKey.Signatures[sourceUserID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+					}
+					masterKey.Signatures[sourceUserID][sourceKeyID] = sourceSig
+				}
+			}
+		}
+	}
+
+	for targetUserID, forUserID := range res.DeviceKeys {
+		for targetKeyID, key := range forUserID {
+			sigMap, err := a.KeyDatabase.CrossSigningSigsForTarget(ctx, req.UserID, targetUserID, gomatrixserverlib.KeyID(targetKeyID))
+			if err != nil {
+				// Stop executing the function if the context was canceled/the deadline was exceeded,
+				// as we can't continue without a valid context.
+				if errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) {
+					return nil
+				}
+				logrus.WithError(err).Errorf("a.KeyDatabase.CrossSigningSigsForTarget failed")
+				continue
+			}
+			if len(sigMap) == 0 {
+				continue
+			}
+			var deviceKey gomatrixserverlib.DeviceKeys
+			if err = json.Unmarshal(key, &deviceKey); err != nil {
+				continue
+			}
+			if deviceKey.Signatures == nil {
+				deviceKey.Signatures = map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+			}
+			for sourceUserID, forSourceUser := range sigMap {
+				for sourceKeyID, sourceSig := range forSourceUser {
+					if _, ok := deviceKey.Signatures[sourceUserID]; !ok {
+						deviceKey.Signatures[sourceUserID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+					}
+					deviceKey.Signatures[sourceUserID][sourceKeyID] = sourceSig
+				}
+			}
+			if js, err := json.Marshal(deviceKey); err == nil {
+				res.DeviceKeys[targetUserID][targetKeyID] = js
+			}
+		}
+	}
+	return nil
+}
+
+func (a *UserInternalAPI) remoteKeysFromDatabase(
+	ctx context.Context, res *api.QueryKeysResponse, respMu *sync.Mutex, domainToDeviceKeys map[string]map[string][]string,
+) map[string]map[string][]string {
+	fetchRemote := make(map[string]map[string][]string)
+	for domain, userToDeviceMap := range domainToDeviceKeys {
+		for userID, deviceIDs := range userToDeviceMap {
+			// we can't safely return keys from the db when all devices are requested as we don't
+			// know if one has just been added.
+			if len(deviceIDs) > 0 {
+				err := a.populateResponseWithDeviceKeysFromDatabase(ctx, res, respMu, userID, deviceIDs)
+				if err == nil {
+					continue
+				}
+				util.GetLogger(ctx).WithError(err).Error("populateResponseWithDeviceKeysFromDatabase")
+			}
+			// fetch device lists from remote
+			if _, ok := fetchRemote[domain]; !ok {
+				fetchRemote[domain] = make(map[string][]string)
+			}
+			fetchRemote[domain][userID] = append(fetchRemote[domain][userID], deviceIDs...)
+
+		}
+	}
+	return fetchRemote
+}
+
+func (a *UserInternalAPI) queryRemoteKeys(
+	ctx context.Context, timeout time.Duration, res *api.QueryKeysResponse,
+	domainToDeviceKeys map[string]map[string][]string, domainToCrossSigningKeys map[string]map[string]struct{},
+) {
+	resultCh := make(chan *gomatrixserverlib.RespQueryKeys, len(domainToDeviceKeys))
+	// allows us to wait until all federation servers have been poked
+	var wg sync.WaitGroup
+	// mutex for writing directly to res (e.g failures)
+	var respMu sync.Mutex
+
+	domains := map[string]struct{}{}
+	for domain := range domainToDeviceKeys {
+		if a.Config.Matrix.IsLocalServerName(gomatrixserverlib.ServerName(domain)) {
+			continue
+		}
+		domains[domain] = struct{}{}
+	}
+	for domain := range domainToCrossSigningKeys {
+		if a.Config.Matrix.IsLocalServerName(gomatrixserverlib.ServerName(domain)) {
+			continue
+		}
+		domains[domain] = struct{}{}
+	}
+	wg.Add(len(domains))
+
+	// fan out
+	for domain := range domains {
+		go a.queryRemoteKeysOnServer(
+			ctx, domain, domainToDeviceKeys[domain], domainToCrossSigningKeys[domain],
+			&wg, &respMu, timeout, resultCh, res,
+		)
+	}
+
+	// Close the result channel when the goroutines have quit so the for .. range exits
+	go func() {
+		wg.Wait()
+		close(resultCh)
+	}()
+
+	processResult := func(result *gomatrixserverlib.RespQueryKeys) {
+		respMu.Lock()
+		defer respMu.Unlock()
+		for userID, nest := range result.DeviceKeys {
+			res.DeviceKeys[userID] = make(map[string]json.RawMessage)
+			for deviceID, deviceKey := range nest {
+				keyJSON, err := json.Marshal(deviceKey)
+				if err != nil {
+					continue
+				}
+				res.DeviceKeys[userID][deviceID] = keyJSON
+			}
+		}
+
+		for userID, body := range result.MasterKeys {
+			res.MasterKeys[userID] = body
+		}
+
+		for userID, body := range result.SelfSigningKeys {
+			res.SelfSigningKeys[userID] = body
+		}
+
+		// TODO: do we want to persist these somewhere now
+		// that we have fetched them?
+	}
+
+	for result := range resultCh {
+		processResult(result)
+	}
+}
+
+func (a *UserInternalAPI) queryRemoteKeysOnServer(
+	ctx context.Context, serverName string, devKeys map[string][]string, crossSigningKeys map[string]struct{},
+	wg *sync.WaitGroup, respMu *sync.Mutex, timeout time.Duration, resultCh chan<- *gomatrixserverlib.RespQueryKeys,
+	res *api.QueryKeysResponse,
+) {
+	defer wg.Done()
+	fedCtx := ctx
+	if timeout > 0 {
+		var cancel context.CancelFunc
+		fedCtx, cancel = context.WithTimeout(ctx, timeout)
+		defer cancel()
+	}
+	// for users who we do not have any knowledge about, try to start doing device list updates for them
+	// by hitting /users/devices - otherwise fallback to /keys/query which has nicer bulk properties but
+	// lack a stream ID.
+	userIDsForAllDevices := map[string]struct{}{}
+	for userID, deviceIDs := range devKeys {
+		if len(deviceIDs) == 0 {
+			userIDsForAllDevices[userID] = struct{}{}
+		}
+	}
+	// for cross-signing keys, it's probably easier just to hit /keys/query if we aren't already doing
+	// a device list update, so we'll populate those back into the /keys/query list if not
+	for userID := range crossSigningKeys {
+		if devKeys == nil {
+			devKeys = map[string][]string{}
+		}
+		if _, ok := userIDsForAllDevices[userID]; !ok {
+			devKeys[userID] = []string{}
+		}
+	}
+	for userID := range userIDsForAllDevices {
+		err := a.Updater.ManualUpdate(context.Background(), gomatrixserverlib.ServerName(serverName), userID)
+		if err != nil {
+			logrus.WithFields(logrus.Fields{
+				logrus.ErrorKey: err,
+				"user_id":       userID,
+				"server":        serverName,
+			}).Error("Failed to manually update device lists for user")
+			// try to do it via /keys/query
+			devKeys[userID] = []string{}
+			continue
+		}
+		// refresh entries from DB: unlike remoteKeysFromDatabase we know we previously had no device info for this
+		// user so the fact that we're populating all devices here isn't a problem so long as we have devices.
+		err = a.populateResponseWithDeviceKeysFromDatabase(ctx, res, respMu, userID, nil)
+		if err != nil {
+			logrus.WithFields(logrus.Fields{
+				logrus.ErrorKey: err,
+				"user_id":       userID,
+				"server":        serverName,
+			}).Error("Failed to manually update device lists for user")
+			// try to do it via /keys/query
+			devKeys[userID] = []string{}
+			continue
+		}
+	}
+	if len(devKeys) == 0 {
+		return
+	}
+	queryKeysResp, err := a.FedClient.QueryKeys(fedCtx, a.Config.Matrix.ServerName, gomatrixserverlib.ServerName(serverName), devKeys)
+	if err == nil {
+		resultCh <- &queryKeysResp
+		return
+	}
+	respMu.Lock()
+	res.Failures[serverName] = map[string]interface{}{
+		"message": err.Error(),
+	}
+	respMu.Unlock()
+
+	// last ditch, use the cache only. This is good for when clients hit /keys/query and the remote server
+	// is down, better to return something than nothing at all. Clients can know about the failure by
+	// inspecting the failures map though so they can know it's a cached response.
+	for userID, dkeys := range devKeys {
+		// drop the error as it's already a failure at this point
+		_ = a.populateResponseWithDeviceKeysFromDatabase(ctx, res, respMu, userID, dkeys)
+	}
+
+	// Sytest expects no failures, if we still could retrieve keys, e.g. from local cache
+	respMu.Lock()
+	if len(res.DeviceKeys) > 0 {
+		delete(res.Failures, serverName)
+	}
+	respMu.Unlock()
+}
+
+func (a *UserInternalAPI) populateResponseWithDeviceKeysFromDatabase(
+	ctx context.Context, res *api.QueryKeysResponse, respMu *sync.Mutex, userID string, deviceIDs []string,
+) error {
+	keys, err := a.KeyDatabase.DeviceKeysForUser(ctx, userID, deviceIDs, false)
+	// if we can't query the db or there are fewer keys than requested, fetch from remote.
+	if err != nil {
+		return fmt.Errorf("DeviceKeysForUser %s %v failed: %w", userID, deviceIDs, err)
+	}
+	if len(keys) < len(deviceIDs) {
+		return fmt.Errorf("DeviceKeysForUser %s returned fewer devices than requested, falling back to remote", userID)
+	}
+	if len(deviceIDs) == 0 && len(keys) == 0 {
+		return fmt.Errorf("DeviceKeysForUser %s returned no keys but wanted all keys, falling back to remote", userID)
+	}
+	respMu.Lock()
+	if res.DeviceKeys[userID] == nil {
+		res.DeviceKeys[userID] = make(map[string]json.RawMessage)
+	}
+	respMu.Unlock()
+
+	for _, key := range keys {
+		if len(key.KeyJSON) == 0 {
+			continue // ignore deleted keys
+		}
+		// inject the display name
+		key.KeyJSON, _ = sjson.SetBytes(key.KeyJSON, "unsigned", struct {
+			DisplayName string `json:"device_display_name,omitempty"`
+		}{key.DisplayName})
+		respMu.Lock()
+		res.DeviceKeys[userID][key.DeviceID] = key.KeyJSON
+		respMu.Unlock()
+	}
+	return nil
+}
+
+func (a *UserInternalAPI) uploadLocalDeviceKeys(ctx context.Context, req *api.PerformUploadKeysRequest, res *api.PerformUploadKeysResponse) {
+	// get a list of devices from the user API that actually exist, as
+	// we won't store keys for devices that don't exist
+	uapidevices := &api.QueryDevicesResponse{}
+	if err := a.QueryDevices(ctx, &api.QueryDevicesRequest{UserID: req.UserID}, uapidevices); err != nil {
+		res.Error = &api.KeyError{
+			Err: err.Error(),
+		}
+		return
+	}
+	if !uapidevices.UserExists {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("user %q does not exist", req.UserID),
+		}
+		return
+	}
+	existingDeviceMap := make(map[string]struct{}, len(uapidevices.Devices))
+	for _, key := range uapidevices.Devices {
+		existingDeviceMap[key.ID] = struct{}{}
+	}
+
+	// Get all of the user existing device keys so we can check for changes.
+	existingKeys, err := a.KeyDatabase.DeviceKeysForUser(ctx, req.UserID, nil, true)
+	if err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("failed to query existing device keys: %s", err.Error()),
+		}
+		return
+	}
+
+	// Work out whether we have device keys in the keyserver for devices that
+	// no longer exist in the user API. This is mostly an exercise to ensure
+	// that we keep some integrity between the two.
+	var toClean []gomatrixserverlib.KeyID
+	for _, k := range existingKeys {
+		if _, ok := existingDeviceMap[k.DeviceID]; !ok {
+			toClean = append(toClean, gomatrixserverlib.KeyID(k.DeviceID))
+		}
+	}
+
+	if len(toClean) > 0 {
+		if err = a.KeyDatabase.DeleteDeviceKeys(ctx, req.UserID, toClean); err != nil {
+			logrus.WithField("user_id", req.UserID).WithError(err).Errorf("Failed to clean up %d stale keyserver device key entries", len(toClean))
+		} else {
+			logrus.WithField("user_id", req.UserID).Debugf("Cleaned up %d stale keyserver device key entries", len(toClean))
+		}
+	}
+
+	var keysToStore []api.DeviceMessage
+
+	if req.OnlyDisplayNameUpdates {
+		for _, existingKey := range existingKeys {
+			for _, newKey := range req.DeviceKeys {
+				switch {
+				case existingKey.UserID != newKey.UserID:
+					continue
+				case existingKey.DeviceID != newKey.DeviceID:
+					continue
+				case existingKey.DisplayName != newKey.DisplayName:
+					existingKey.DisplayName = newKey.DisplayName
+				}
+			}
+			keysToStore = append(keysToStore, existingKey)
+		}
+	} else {
+		// assert that the user ID / device ID are not lying for each key
+		for _, key := range req.DeviceKeys {
+			var serverName gomatrixserverlib.ServerName
+			_, serverName, err = gomatrixserverlib.SplitID('@', key.UserID)
+			if err != nil {
+				continue // ignore invalid users
+			}
+			if !a.Config.Matrix.IsLocalServerName(serverName) {
+				continue // ignore remote users
+			}
+			if len(key.KeyJSON) == 0 {
+				keysToStore = append(keysToStore, key.WithStreamID(0))
+				continue // deleted keys don't need sanity checking
+			}
+			// check that the device in question actually exists in the user
+			// API before we try and store a key for it
+			if _, ok := existingDeviceMap[key.DeviceID]; !ok {
+				continue
+			}
+			gotUserID := gjson.GetBytes(key.KeyJSON, "user_id").Str
+			gotDeviceID := gjson.GetBytes(key.KeyJSON, "device_id").Str
+			if gotUserID == key.UserID && gotDeviceID == key.DeviceID {
+				keysToStore = append(keysToStore, key.WithStreamID(0))
+				continue
+			}
+
+			res.KeyError(key.UserID, key.DeviceID, &api.KeyError{
+				Err: fmt.Sprintf(
+					"user_id or device_id mismatch: users: %s - %s, devices: %s - %s",
+					gotUserID, key.UserID, gotDeviceID, key.DeviceID,
+				),
+			})
+		}
+	}
+
+	// store the device keys and emit changes
+	err = a.KeyDatabase.StoreLocalDeviceKeys(ctx, keysToStore)
+	if err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("failed to store device keys: %s", err.Error()),
+		}
+		return
+	}
+	err = emitDeviceKeyChanges(a.KeyChangeProducer, existingKeys, keysToStore, req.OnlyDisplayNameUpdates)
+	if err != nil {
+		util.GetLogger(ctx).Errorf("Failed to emitDeviceKeyChanges: %s", err)
+	}
+}
+
+func (a *UserInternalAPI) uploadOneTimeKeys(ctx context.Context, req *api.PerformUploadKeysRequest, res *api.PerformUploadKeysResponse) {
+	if req.UserID == "" {
+		res.Error = &api.KeyError{
+			Err: "user ID  missing",
+		}
+	}
+	if req.DeviceID != "" && len(req.OneTimeKeys) == 0 {
+		counts, err := a.KeyDatabase.OneTimeKeysCount(ctx, req.UserID, req.DeviceID)
+		if err != nil {
+			res.Error = &api.KeyError{
+				Err: fmt.Sprintf("a.KeyDatabase.OneTimeKeysCount: %s", err),
+			}
+		}
+		if counts != nil {
+			res.OneTimeKeyCounts = append(res.OneTimeKeyCounts, *counts)
+		}
+		return
+	}
+	for _, key := range req.OneTimeKeys {
+		// grab existing keys based on (user/device/algorithm/key ID)
+		keyIDsWithAlgorithms := make([]string, len(key.KeyJSON))
+		i := 0
+		for keyIDWithAlgo := range key.KeyJSON {
+			keyIDsWithAlgorithms[i] = keyIDWithAlgo
+			i++
+		}
+		existingKeys, err := a.KeyDatabase.ExistingOneTimeKeys(ctx, req.UserID, req.DeviceID, keyIDsWithAlgorithms)
+		if err != nil {
+			res.KeyError(req.UserID, req.DeviceID, &api.KeyError{
+				Err: "failed to query existing one-time keys: " + err.Error(),
+			})
+			continue
+		}
+		for keyIDWithAlgo := range existingKeys {
+			// if keys exist and the JSON doesn't match, error out as the key already exists
+			if !bytes.Equal(existingKeys[keyIDWithAlgo], key.KeyJSON[keyIDWithAlgo]) {
+				res.KeyError(req.UserID, req.DeviceID, &api.KeyError{
+					Err: fmt.Sprintf("%s device %s: algorithm / key ID %s one-time key already exists", req.UserID, req.DeviceID, keyIDWithAlgo),
+				})
+				continue
+			}
+		}
+		// store one-time keys
+		counts, err := a.KeyDatabase.StoreOneTimeKeys(ctx, key)
+		if err != nil {
+			res.KeyError(req.UserID, req.DeviceID, &api.KeyError{
+				Err: fmt.Sprintf("%s device %s : failed to store one-time keys: %s", req.UserID, req.DeviceID, err.Error()),
+			})
+			continue
+		}
+		// collect counts
+		res.OneTimeKeyCounts = append(res.OneTimeKeyCounts, *counts)
+	}
+
+}
+
+func emitDeviceKeyChanges(producer KeyChangeProducer, existing, new []api.DeviceMessage, onlyUpdateDisplayName bool) error {
+	// if we only want to update the display names, we can skip the checks below
+	if onlyUpdateDisplayName {
+		return producer.ProduceKeyChanges(new)
+	}
+	// find keys in new that are not in existing
+	var keysAdded []api.DeviceMessage
+	for _, newKey := range new {
+		exists := false
+		for _, existingKey := range existing {
+			// Do not treat the absence of keys as equal, or else we will not emit key changes
+			// when users delete devices which never had a key to begin with as both KeyJSONs are nil.
+			if existingKey.DeviceKeysEqual(&newKey) {
+				exists = true
+				break
+			}
+		}
+		if !exists {
+			keysAdded = append(keysAdded, newKey)
+		}
+	}
+	return producer.ProduceKeyChanges(keysAdded)
+}
diff --git a/userapi/internal/key_api_test.go b/userapi/internal/key_api_test.go
new file mode 100644
index 00000000..fc7e7e0d
--- /dev/null
+++ b/userapi/internal/key_api_test.go
@@ -0,0 +1,161 @@
+package internal_test
+
+import (
+	"context"
+	"reflect"
+	"testing"
+
+	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/dendrite/test"
+	"github.com/matrix-org/dendrite/test/testrig"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/internal"
+	"github.com/matrix-org/dendrite/userapi/storage"
+)
+
+func mustCreateDatabase(t *testing.T, dbType test.DBType) (storage.KeyDatabase, func()) {
+	t.Helper()
+	connStr, close := test.PrepareDBConnectionString(t, dbType)
+	base, _, _ := testrig.Base(nil)
+	db, err := storage.NewKeyDatabase(base, &config.DatabaseOptions{
+		ConnectionString: config.DataSource(connStr),
+	})
+	if err != nil {
+		t.Fatalf("failed to create new user db: %v", err)
+	}
+	return db, func() {
+		base.Close()
+		close()
+	}
+}
+
+func Test_QueryDeviceMessages(t *testing.T) {
+	alice := test.NewUser(t)
+	type args struct {
+		req *api.QueryDeviceMessagesRequest
+		res *api.QueryDeviceMessagesResponse
+	}
+	tests := []struct {
+		name    string
+		args    args
+		wantErr bool
+		want    *api.QueryDeviceMessagesResponse
+	}{
+		{
+			name: "no existing keys",
+			args: args{
+				req: &api.QueryDeviceMessagesRequest{
+					UserID: "@doesNotExist:localhost",
+				},
+				res: &api.QueryDeviceMessagesResponse{},
+			},
+			want: &api.QueryDeviceMessagesResponse{},
+		},
+		{
+			name: "existing user returns devices",
+			args: args{
+				req: &api.QueryDeviceMessagesRequest{
+					UserID: alice.ID,
+				},
+				res: &api.QueryDeviceMessagesResponse{},
+			},
+			want: &api.QueryDeviceMessagesResponse{
+				StreamID: 6,
+				Devices: []api.DeviceMessage{
+					{
+						Type: api.TypeDeviceKeyUpdate, StreamID: 5, DeviceKeys: &api.DeviceKeys{
+							DeviceID:    "myDevice",
+							DisplayName: "first device",
+							UserID:      alice.ID,
+							KeyJSON:     []byte("ghi"),
+						},
+					},
+					{
+						Type: api.TypeDeviceKeyUpdate, StreamID: 6, DeviceKeys: &api.DeviceKeys{
+							DeviceID:    "mySecondDevice",
+							DisplayName: "second device",
+							UserID:      alice.ID,
+							KeyJSON:     []byte("jkl"),
+						}, // streamID 6
+					},
+				},
+			},
+		},
+	}
+
+	deviceMessages := []api.DeviceMessage{
+		{ // not the user we're looking for
+			Type: api.TypeDeviceKeyUpdate, DeviceKeys: &api.DeviceKeys{
+				UserID: "@doesNotExist:localhost",
+			},
+			// streamID 1 for this user
+		},
+		{ // empty keyJSON will be ignored
+			Type: api.TypeDeviceKeyUpdate, DeviceKeys: &api.DeviceKeys{
+				DeviceID: "myDevice",
+				UserID:   alice.ID,
+			}, // streamID 1
+		},
+		{
+			Type: api.TypeDeviceKeyUpdate, DeviceKeys: &api.DeviceKeys{
+				DeviceID: "myDevice",
+				UserID:   alice.ID,
+				KeyJSON:  []byte("abc"),
+			}, // streamID 2
+		},
+		{
+			Type: api.TypeDeviceKeyUpdate, DeviceKeys: &api.DeviceKeys{
+				DeviceID: "myDevice",
+				UserID:   alice.ID,
+				KeyJSON:  []byte("def"),
+			}, // streamID 3
+		},
+		{
+			Type: api.TypeDeviceKeyUpdate, DeviceKeys: &api.DeviceKeys{
+				DeviceID: "myDevice",
+				UserID:   alice.ID,
+				KeyJSON:  []byte(""),
+			}, // streamID 4
+		},
+		{
+			Type: api.TypeDeviceKeyUpdate, DeviceKeys: &api.DeviceKeys{
+				DeviceID:    "myDevice",
+				DisplayName: "first device",
+				UserID:      alice.ID,
+				KeyJSON:     []byte("ghi"),
+			}, // streamID 5
+		},
+		{
+			Type: api.TypeDeviceKeyUpdate, DeviceKeys: &api.DeviceKeys{
+				DeviceID:    "mySecondDevice",
+				UserID:      alice.ID,
+				KeyJSON:     []byte("jkl"),
+				DisplayName: "second device",
+			}, // streamID 6
+		},
+	}
+	ctx := context.Background()
+
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		db, closeDB := mustCreateDatabase(t, dbType)
+		defer closeDB()
+		if err := db.StoreLocalDeviceKeys(ctx, deviceMessages); err != nil {
+			t.Fatalf("failed to store local devicesKeys")
+		}
+
+		for _, tt := range tests {
+			t.Run(tt.name, func(t *testing.T) {
+				a := &internal.UserInternalAPI{
+					KeyDatabase: db,
+				}
+				if err := a.QueryDeviceMessages(ctx, tt.args.req, tt.args.res); (err != nil) != tt.wantErr {
+					t.Errorf("QueryDeviceMessages() error = %v, wantErr %v", err, tt.wantErr)
+				}
+				got := tt.args.res
+				if !reflect.DeepEqual(got, tt.want) {
+					t.Errorf("QueryDeviceMessages(): got:\n%+v, want:\n%+v", got, tt.want)
+				}
+			})
+		}
+	})
+}
diff --git a/userapi/internal/api.go b/userapi/internal/user_api.go
index 0bb480da..1cbd9719 100644
--- a/userapi/internal/api.go
+++ b/userapi/internal/user_api.go
@@ -23,6 +23,7 @@ import (
 	"strconv"
 	"time"
 
+	fedsenderapi "github.com/matrix-org/dendrite/federationapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	"github.com/sirupsen/logrus"
@@ -32,7 +33,6 @@ import (
 	"github.com/matrix-org/dendrite/internal/eventutil"
 	"github.com/matrix-org/dendrite/internal/pushgateway"
 	"github.com/matrix-org/dendrite/internal/sqlutil"
-	keyapi "github.com/matrix-org/dendrite/keyserver/api"
 	rsapi "github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/setup/config"
 	synctypes "github.com/matrix-org/dendrite/syncapi/types"
@@ -44,17 +44,19 @@ import (
 )
 
 type UserInternalAPI struct {
-	DB           storage.Database
-	SyncProducer *producers.SyncAPI
-	Config       *config.UserAPI
+	DB                storage.UserDatabase
+	KeyDatabase       storage.KeyDatabase
+	SyncProducer      *producers.SyncAPI
+	KeyChangeProducer *producers.KeyChange
+	Config            *config.UserAPI
 
 	DisableTLSValidation bool
 	// AppServices is the list of all registered AS
 	AppServices []config.ApplicationService
-	KeyAPI      keyapi.UserKeyAPI
 	RSAPI       rsapi.UserRoomserverAPI
 	PgClient    pushgateway.Client
-	Cfg         *config.UserAPI
+	FedClient   fedsenderapi.KeyserverFederationAPI
+	Updater     *DeviceListUpdater
 }
 
 func (a *UserInternalAPI) InputAccountData(ctx context.Context, req *api.InputAccountDataRequest, res *api.InputAccountDataResponse) error {
@@ -221,7 +223,7 @@ func (a *UserInternalAPI) PerformAccountCreation(ctx context.Context, req *api.P
 		return fmt.Errorf("a.DB.SetDisplayName: %w", err)
 	}
 
-	postRegisterJoinRooms(a.Cfg, acc, a.RSAPI)
+	postRegisterJoinRooms(a.Config, acc, a.RSAPI)
 
 	res.AccountCreated = true
 	res.Account = acc
@@ -293,14 +295,14 @@ func (a *UserInternalAPI) PerformDeviceDeletion(ctx context.Context, req *api.Pe
 		return err
 	}
 	// Ask the keyserver to delete device keys and signatures for those devices
-	deleteReq := &keyapi.PerformDeleteKeysRequest{
+	deleteReq := &api.PerformDeleteKeysRequest{
 		UserID: req.UserID,
 	}
 	for _, keyID := range req.DeviceIDs {
 		deleteReq.KeyIDs = append(deleteReq.KeyIDs, gomatrixserverlib.KeyID(keyID))
 	}
-	deleteRes := &keyapi.PerformDeleteKeysResponse{}
-	if err := a.KeyAPI.PerformDeleteKeys(ctx, deleteReq, deleteRes); err != nil {
+	deleteRes := &api.PerformDeleteKeysResponse{}
+	if err := a.PerformDeleteKeys(ctx, deleteReq, deleteRes); err != nil {
 		return err
 	}
 	if err := deleteRes.Error; err != nil {
@@ -311,17 +313,17 @@ func (a *UserInternalAPI) PerformDeviceDeletion(ctx context.Context, req *api.Pe
 }
 
 func (a *UserInternalAPI) deviceListUpdate(userID string, deviceIDs []string) error {
-	deviceKeys := make([]keyapi.DeviceKeys, len(deviceIDs))
+	deviceKeys := make([]api.DeviceKeys, len(deviceIDs))
 	for i, did := range deviceIDs {
-		deviceKeys[i] = keyapi.DeviceKeys{
+		deviceKeys[i] = api.DeviceKeys{
 			UserID:   userID,
 			DeviceID: did,
 			KeyJSON:  nil,
 		}
 	}
 
-	var uploadRes keyapi.PerformUploadKeysResponse
-	if err := a.KeyAPI.PerformUploadKeys(context.Background(), &keyapi.PerformUploadKeysRequest{
+	var uploadRes api.PerformUploadKeysResponse
+	if err := a.PerformUploadKeys(context.Background(), &api.PerformUploadKeysRequest{
 		UserID:     userID,
 		DeviceKeys: deviceKeys,
 	}, &uploadRes); err != nil {
@@ -385,10 +387,10 @@ func (a *UserInternalAPI) PerformDeviceUpdate(ctx context.Context, req *api.Perf
 	}
 	if req.DisplayName != nil && dev.DisplayName != *req.DisplayName {
 		// display name has changed: update the device key
-		var uploadRes keyapi.PerformUploadKeysResponse
-		if err := a.KeyAPI.PerformUploadKeys(context.Background(), &keyapi.PerformUploadKeysRequest{
+		var uploadRes api.PerformUploadKeysResponse
+		if err := a.PerformUploadKeys(context.Background(), &api.PerformUploadKeysRequest{
 			UserID: req.RequestingUserID,
-			DeviceKeys: []keyapi.DeviceKeys{
+			DeviceKeys: []api.DeviceKeys{
 				{
 					DeviceID:    dev.ID,
 					DisplayName: *req.DisplayName,
diff --git a/userapi/producers/keychange.go b/userapi/producers/keychange.go
new file mode 100644
index 00000000..da6cea31
--- /dev/null
+++ b/userapi/producers/keychange.go
@@ -0,0 +1,107 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package producers
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/matrix-org/dendrite/setup/jetstream"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/storage"
+	"github.com/nats-io/nats.go"
+	"github.com/sirupsen/logrus"
+)
+
+// KeyChange produces key change events for the sync API and federation sender to consume
+type KeyChange struct {
+	Topic     string
+	JetStream JetStreamPublisher
+	DB        storage.KeyChangeDatabase
+}
+
+// ProduceKeyChanges creates new change events for each key
+func (p *KeyChange) ProduceKeyChanges(keys []api.DeviceMessage) error {
+	userToDeviceCount := make(map[string]int)
+	for _, key := range keys {
+		id, err := p.DB.StoreKeyChange(context.Background(), key.UserID)
+		if err != nil {
+			return err
+		}
+		key.DeviceChangeID = id
+		value, err := json.Marshal(key)
+		if err != nil {
+			return err
+		}
+
+		m := &nats.Msg{
+			Subject: p.Topic,
+			Header:  nats.Header{},
+		}
+		m.Header.Set(jetstream.UserID, key.UserID)
+		m.Data = value
+
+		_, err = p.JetStream.PublishMsg(m)
+		if err != nil {
+			return err
+		}
+
+		userToDeviceCount[key.UserID]++
+	}
+	for userID, count := range userToDeviceCount {
+		logrus.WithFields(logrus.Fields{
+			"user_id":         userID,
+			"num_key_changes": count,
+		}).Tracef("Produced to key change topic '%s'", p.Topic)
+	}
+	return nil
+}
+
+func (p *KeyChange) ProduceSigningKeyUpdate(key api.CrossSigningKeyUpdate) error {
+	output := &api.DeviceMessage{
+		Type: api.TypeCrossSigningUpdate,
+		OutputCrossSigningKeyUpdate: &api.OutputCrossSigningKeyUpdate{
+			CrossSigningKeyUpdate: key,
+		},
+	}
+
+	id, err := p.DB.StoreKeyChange(context.Background(), key.UserID)
+	if err != nil {
+		return err
+	}
+	output.DeviceChangeID = id
+
+	value, err := json.Marshal(output)
+	if err != nil {
+		return err
+	}
+
+	m := &nats.Msg{
+		Subject: p.Topic,
+		Header:  nats.Header{},
+	}
+	m.Header.Set(jetstream.UserID, key.UserID)
+	m.Data = value
+
+	_, err = p.JetStream.PublishMsg(m)
+	if err != nil {
+		return err
+	}
+
+	logrus.WithFields(logrus.Fields{
+		"user_id": key.UserID,
+	}).Tracef("Produced to cross-signing update topic '%s'", p.Topic)
+	return nil
+}
diff --git a/userapi/producers/syncapi.go b/userapi/producers/syncapi.go
index 51eaa985..165de899 100644
--- a/userapi/producers/syncapi.go
+++ b/userapi/producers/syncapi.go
@@ -19,13 +19,13 @@ type JetStreamPublisher interface {
 
 // SyncAPI produces messages for the Sync API server to consume.
 type SyncAPI struct {
-	db                    storage.Database
+	db                    storage.Notification
 	producer              JetStreamPublisher
 	clientDataTopic       string
 	notificationDataTopic string
 }
 
-func NewSyncAPI(db storage.Database, js JetStreamPublisher, clientDataTopic string, notificationDataTopic string) *SyncAPI {
+func NewSyncAPI(db storage.UserDatabase, js JetStreamPublisher, clientDataTopic string, notificationDataTopic string) *SyncAPI {
 	return &SyncAPI{
 		db:                    db,
 		producer:              js,
diff --git a/userapi/storage/interface.go b/userapi/storage/interface.go
index c22b7658..27837886 100644
--- a/userapi/storage/interface.go
+++ b/userapi/storage/interface.go
@@ -90,7 +90,7 @@ type KeyBackup interface {
 
 type LoginToken interface {
 	// CreateLoginToken generates a token, stores and returns it. The lifetime is
-	// determined by the loginTokenLifetime given to the Database constructor.
+	// determined by the loginTokenLifetime given to the UserDatabase constructor.
 	CreateLoginToken(ctx context.Context, data *api.LoginTokenData) (*api.LoginTokenMetadata, error)
 
 	// RemoveLoginToken removes the named token (and may clean up other expired tokens).
@@ -130,7 +130,7 @@ type Notification interface {
 	DeleteOldNotifications(ctx context.Context) error
 }
 
-type Database interface {
+type UserDatabase interface {
 	Account
 	AccountData
 	Device
@@ -144,6 +144,78 @@ type Database interface {
 	ThreePID
 }
 
+type KeyChangeDatabase interface {
+	// StoreKeyChange stores key change metadata and returns the device change ID which represents the position in the /sync stream for this device change.
+	// `userID` is the the user who has changed their keys in some way.
+	StoreKeyChange(ctx context.Context, userID string) (int64, error)
+}
+
+type KeyDatabase interface {
+	KeyChangeDatabase
+	// ExistingOneTimeKeys returns a map of keyIDWithAlgorithm to key JSON for the given parameters. If no keys exist with this combination
+	// of user/device/key/algorithm 4-uple then it is omitted from the map. Returns an error when failing to communicate with the database.
+	ExistingOneTimeKeys(ctx context.Context, userID, deviceID string, keyIDsWithAlgorithms []string) (map[string]json.RawMessage, error)
+
+	// StoreOneTimeKeys persists the given one-time keys.
+	StoreOneTimeKeys(ctx context.Context, keys api.OneTimeKeys) (*api.OneTimeKeysCount, error)
+
+	// OneTimeKeysCount returns a count of all OTKs for this device.
+	OneTimeKeysCount(ctx context.Context, userID, deviceID string) (*api.OneTimeKeysCount, error)
+
+	// DeviceKeysJSON populates the KeyJSON for the given keys. If any proided `keys` have a `KeyJSON` or `StreamID` already then it will be replaced.
+	DeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error
+
+	// StoreLocalDeviceKeys persists the given keys. Keys with the same user ID and device ID will be replaced. An empty KeyJSON removes the key
+	// for this (user, device).
+	// The `StreamID` for each message is set on successful insertion. In the event the key already exists, the existing StreamID is set.
+	// Returns an error if there was a problem storing the keys.
+	StoreLocalDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error
+
+	// StoreRemoteDeviceKeys persists the given keys. Keys with the same user ID and device ID will be replaced. An empty KeyJSON removes the key
+	// for this (user, device). Does not modify the stream ID for keys. User IDs in `clearUserIDs` will have all their device keys deleted prior
+	// to insertion - use this when you have a complete snapshot of a user's keys in order to track device deletions correctly.
+	StoreRemoteDeviceKeys(ctx context.Context, keys []api.DeviceMessage, clearUserIDs []string) error
+
+	// PrevIDsExists returns true if all prev IDs exist for this user.
+	PrevIDsExists(ctx context.Context, userID string, prevIDs []int64) (bool, error)
+
+	// DeviceKeysForUser returns the device keys for the device IDs given. If the length of deviceIDs is 0, all devices are selected.
+	// If there are some missing keys, they are omitted from the returned slice. There is no ordering on the returned slice.
+	DeviceKeysForUser(ctx context.Context, userID string, deviceIDs []string, includeEmpty bool) ([]api.DeviceMessage, error)
+
+	// DeleteDeviceKeys removes the device keys for a given user/device, and any accompanying
+	// cross-signing signatures relating to that device.
+	DeleteDeviceKeys(ctx context.Context, userID string, deviceIDs []gomatrixserverlib.KeyID) error
+
+	// ClaimKeys based on the 3-uple of user_id, device_id and algorithm name. Returns the keys claimed. Returns no error if a key
+	// cannot be claimed or if none exist for this (user, device, algorithm), instead it is omitted from the returned slice.
+	ClaimKeys(ctx context.Context, userToDeviceToAlgorithm map[string]map[string]string) ([]api.OneTimeKeys, error)
+
+	// KeyChanges returns a list of user IDs who have modified their keys from the offset given (exclusive) to the offset given (inclusive).
+	// A to offset of types.OffsetNewest means no upper limit.
+	// Returns the offset of the latest key change.
+	KeyChanges(ctx context.Context, fromOffset, toOffset int64) (userIDs []string, latestOffset int64, err error)
+
+	// StaleDeviceLists returns a list of user IDs ending with the domains provided who have stale device lists.
+	// If no domains are given, all user IDs with stale device lists are returned.
+	StaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error)
+
+	// MarkDeviceListStale sets the stale bit for this user to isStale.
+	MarkDeviceListStale(ctx context.Context, userID string, isStale bool) error
+
+	CrossSigningKeysForUser(ctx context.Context, userID string) (map[gomatrixserverlib.CrossSigningKeyPurpose]gomatrixserverlib.CrossSigningKey, error)
+	CrossSigningKeysDataForUser(ctx context.Context, userID string) (types.CrossSigningKeyMap, error)
+	CrossSigningSigsForTarget(ctx context.Context, originUserID, targetUserID string, targetKeyID gomatrixserverlib.KeyID) (types.CrossSigningSigMap, error)
+
+	StoreCrossSigningKeysForUser(ctx context.Context, userID string, keyMap types.CrossSigningKeyMap) error
+	StoreCrossSigningSigsForTarget(ctx context.Context, originUserID string, originKeyID gomatrixserverlib.KeyID, targetUserID string, targetKeyID gomatrixserverlib.KeyID, signature gomatrixserverlib.Base64Bytes) error
+
+	DeleteStaleDeviceLists(
+		ctx context.Context,
+		userIDs []string,
+	) error
+}
+
 type Statistics interface {
 	UserStatistics(ctx context.Context) (*types.UserStatistics, *types.DatabaseEngine, error)
 	DailyRoomsMessages(ctx context.Context, serverName gomatrixserverlib.ServerName) (stats types.MessageStats, activeRooms, activeE2EERooms int64, err error)
diff --git a/userapi/storage/postgres/account_data_table.go b/userapi/storage/postgres/account_data_table.go
index 2a4777d7..05716037 100644
--- a/userapi/storage/postgres/account_data_table.go
+++ b/userapi/storage/postgres/account_data_table.go
@@ -78,7 +78,13 @@ func (s *accountDataStatements) InsertAccountData(
 	roomID, dataType string, content json.RawMessage,
 ) (err error) {
 	stmt := sqlutil.TxStmt(txn, s.insertAccountDataStmt)
-	_, err = stmt.ExecContext(ctx, localpart, serverName, roomID, dataType, content)
+	// Empty/nil json.RawMessage is not interpreted as "nil", so use *json.RawMessage
+	// when passing the data to trigger "NOT NULL" constraint
+	var data *json.RawMessage
+	if len(content) > 0 {
+		data = &content
+	}
+	_, err = stmt.ExecContext(ctx, localpart, serverName, roomID, dataType, data)
 	return
 }
 
diff --git a/userapi/storage/postgres/cross_signing_keys_table.go b/userapi/storage/postgres/cross_signing_keys_table.go
new file mode 100644
index 00000000..c0ecbd30
--- /dev/null
+++ b/userapi/storage/postgres/cross_signing_keys_table.go
@@ -0,0 +1,102 @@
+// Copyright 2021 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+	"github.com/matrix-org/dendrite/userapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+var crossSigningKeysSchema = `
+CREATE TABLE IF NOT EXISTS keyserver_cross_signing_keys (
+    user_id TEXT NOT NULL,
+	key_type SMALLINT NOT NULL,
+	key_data TEXT NOT NULL,
+	PRIMARY KEY (user_id, key_type)
+);
+`
+
+const selectCrossSigningKeysForUserSQL = "" +
+	"SELECT key_type, key_data FROM keyserver_cross_signing_keys" +
+	" WHERE user_id = $1"
+
+const upsertCrossSigningKeysForUserSQL = "" +
+	"INSERT INTO keyserver_cross_signing_keys (user_id, key_type, key_data)" +
+	" VALUES($1, $2, $3)" +
+	" ON CONFLICT (user_id, key_type) DO UPDATE SET key_data = $3"
+
+type crossSigningKeysStatements struct {
+	db                                *sql.DB
+	selectCrossSigningKeysForUserStmt *sql.Stmt
+	upsertCrossSigningKeysForUserStmt *sql.Stmt
+}
+
+func NewPostgresCrossSigningKeysTable(db *sql.DB) (tables.CrossSigningKeys, error) {
+	s := &crossSigningKeysStatements{
+		db: db,
+	}
+	_, err := db.Exec(crossSigningKeysSchema)
+	if err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.selectCrossSigningKeysForUserStmt, selectCrossSigningKeysForUserSQL},
+		{&s.upsertCrossSigningKeysForUserStmt, upsertCrossSigningKeysForUserSQL},
+	}.Prepare(db)
+}
+
+func (s *crossSigningKeysStatements) SelectCrossSigningKeysForUser(
+	ctx context.Context, txn *sql.Tx, userID string,
+) (r types.CrossSigningKeyMap, err error) {
+	rows, err := sqlutil.TxStmt(txn, s.selectCrossSigningKeysForUserStmt).QueryContext(ctx, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectCrossSigningKeysForUserStmt: rows.close() failed")
+	r = types.CrossSigningKeyMap{}
+	for rows.Next() {
+		var keyTypeInt int16
+		var keyData gomatrixserverlib.Base64Bytes
+		if err := rows.Scan(&keyTypeInt, &keyData); err != nil {
+			return nil, err
+		}
+		keyType, ok := types.KeyTypeIntToPurpose[keyTypeInt]
+		if !ok {
+			return nil, fmt.Errorf("unknown key purpose int %d", keyTypeInt)
+		}
+		r[keyType] = keyData
+	}
+	return
+}
+
+func (s *crossSigningKeysStatements) UpsertCrossSigningKeysForUser(
+	ctx context.Context, txn *sql.Tx, userID string, keyType gomatrixserverlib.CrossSigningKeyPurpose, keyData gomatrixserverlib.Base64Bytes,
+) error {
+	keyTypeInt, ok := types.KeyTypePurposeToInt[keyType]
+	if !ok {
+		return fmt.Errorf("unknown key purpose %q", keyType)
+	}
+	if _, err := sqlutil.TxStmt(txn, s.upsertCrossSigningKeysForUserStmt).ExecContext(ctx, userID, keyTypeInt, keyData); err != nil {
+		return fmt.Errorf("s.upsertCrossSigningKeysForUserStmt: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/storage/postgres/cross_signing_sigs_table.go b/userapi/storage/postgres/cross_signing_sigs_table.go
new file mode 100644
index 00000000..b0117145
--- /dev/null
+++ b/userapi/storage/postgres/cross_signing_sigs_table.go
@@ -0,0 +1,131 @@
+// Copyright 2021 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/storage/postgres/deltas"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+	"github.com/matrix-org/dendrite/userapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+var crossSigningSigsSchema = `
+CREATE TABLE IF NOT EXISTS keyserver_cross_signing_sigs (
+    origin_user_id TEXT NOT NULL,
+	origin_key_id TEXT NOT NULL,
+	target_user_id TEXT NOT NULL,
+	target_key_id TEXT NOT NULL,
+	signature TEXT NOT NULL,
+	PRIMARY KEY (origin_user_id, origin_key_id, target_user_id, target_key_id)
+);
+
+CREATE INDEX IF NOT EXISTS keyserver_cross_signing_sigs_idx ON keyserver_cross_signing_sigs (origin_user_id, target_user_id, target_key_id);
+`
+
+const selectCrossSigningSigsForTargetSQL = "" +
+	"SELECT origin_user_id, origin_key_id, signature FROM keyserver_cross_signing_sigs" +
+	" WHERE (origin_user_id = $1 OR origin_user_id = $2) AND target_user_id = $2 AND target_key_id = $3"
+
+const upsertCrossSigningSigsForTargetSQL = "" +
+	"INSERT INTO keyserver_cross_signing_sigs (origin_user_id, origin_key_id, target_user_id, target_key_id, signature)" +
+	" VALUES($1, $2, $3, $4, $5)" +
+	" ON CONFLICT (origin_user_id, origin_key_id, target_user_id, target_key_id) DO UPDATE SET signature = $5"
+
+const deleteCrossSigningSigsForTargetSQL = "" +
+	"DELETE FROM keyserver_cross_signing_sigs WHERE target_user_id=$1 AND target_key_id=$2"
+
+type crossSigningSigsStatements struct {
+	db                                  *sql.DB
+	selectCrossSigningSigsForTargetStmt *sql.Stmt
+	upsertCrossSigningSigsForTargetStmt *sql.Stmt
+	deleteCrossSigningSigsForTargetStmt *sql.Stmt
+}
+
+func NewPostgresCrossSigningSigsTable(db *sql.DB) (tables.CrossSigningSigs, error) {
+	s := &crossSigningSigsStatements{
+		db: db,
+	}
+	_, err := db.Exec(crossSigningSigsSchema)
+	if err != nil {
+		return nil, err
+	}
+
+	m := sqlutil.NewMigrator(db)
+	m.AddMigrations(sqlutil.Migration{
+		Version: "keyserver: cross signing signature indexes",
+		Up:      deltas.UpFixCrossSigningSignatureIndexes,
+	})
+	if err = m.Up(context.Background()); err != nil {
+		return nil, err
+	}
+
+	return s, sqlutil.StatementList{
+		{&s.selectCrossSigningSigsForTargetStmt, selectCrossSigningSigsForTargetSQL},
+		{&s.upsertCrossSigningSigsForTargetStmt, upsertCrossSigningSigsForTargetSQL},
+		{&s.deleteCrossSigningSigsForTargetStmt, deleteCrossSigningSigsForTargetSQL},
+	}.Prepare(db)
+}
+
+func (s *crossSigningSigsStatements) SelectCrossSigningSigsForTarget(
+	ctx context.Context, txn *sql.Tx, originUserID, targetUserID string, targetKeyID gomatrixserverlib.KeyID,
+) (r types.CrossSigningSigMap, err error) {
+	rows, err := sqlutil.TxStmt(txn, s.selectCrossSigningSigsForTargetStmt).QueryContext(ctx, originUserID, targetUserID, targetKeyID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectCrossSigningSigsForTargetStmt: rows.close() failed")
+	r = types.CrossSigningSigMap{}
+	for rows.Next() {
+		var userID string
+		var keyID gomatrixserverlib.KeyID
+		var signature gomatrixserverlib.Base64Bytes
+		if err := rows.Scan(&userID, &keyID, &signature); err != nil {
+			return nil, err
+		}
+		if _, ok := r[userID]; !ok {
+			r[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+		}
+		r[userID][keyID] = signature
+	}
+	return
+}
+
+func (s *crossSigningSigsStatements) UpsertCrossSigningSigsForTarget(
+	ctx context.Context, txn *sql.Tx,
+	originUserID string, originKeyID gomatrixserverlib.KeyID,
+	targetUserID string, targetKeyID gomatrixserverlib.KeyID,
+	signature gomatrixserverlib.Base64Bytes,
+) error {
+	if _, err := sqlutil.TxStmt(txn, s.upsertCrossSigningSigsForTargetStmt).ExecContext(ctx, originUserID, originKeyID, targetUserID, targetKeyID, signature); err != nil {
+		return fmt.Errorf("s.upsertCrossSigningSigsForTargetStmt: %w", err)
+	}
+	return nil
+}
+
+func (s *crossSigningSigsStatements) DeleteCrossSigningSigsForTarget(
+	ctx context.Context, txn *sql.Tx,
+	targetUserID string, targetKeyID gomatrixserverlib.KeyID,
+) error {
+	if _, err := sqlutil.TxStmt(txn, s.deleteCrossSigningSigsForTargetStmt).ExecContext(ctx, targetUserID, targetKeyID); err != nil {
+		return fmt.Errorf("s.deleteCrossSigningSigsForTargetStmt: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/storage/postgres/deltas/2022012016470000_key_changes.go b/userapi/storage/postgres/deltas/2022012016470000_key_changes.go
new file mode 100644
index 00000000..0cfe9e79
--- /dev/null
+++ b/userapi/storage/postgres/deltas/2022012016470000_key_changes.go
@@ -0,0 +1,69 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package deltas
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+func UpRefactorKeyChanges(ctx context.Context, tx *sql.Tx) error {
+	// start counting from the last max offset, else 0. We need to do a count(*) first to see if there
+	// even are entries in this table to know if we can query for log_offset. Without the count then
+	// the query to SELECT the max log offset fails on new Dendrite instances as log_offset doesn't
+	// exist on that table. Even though we discard the error, the txn is tainted and gets aborted :/
+	var count int
+	_ = tx.QueryRowContext(ctx, `SELECT count(*) FROM keyserver_key_changes`).Scan(&count)
+	if count > 0 {
+		var maxOffset int64
+		_ = tx.QueryRowContext(ctx, `SELECT coalesce(MAX(log_offset), 0) AS offset FROM keyserver_key_changes`).Scan(&maxOffset)
+		if _, err := tx.ExecContext(ctx, fmt.Sprintf(`CREATE SEQUENCE IF NOT EXISTS keyserver_key_changes_seq START %d`, maxOffset)); err != nil {
+			return fmt.Errorf("failed to CREATE SEQUENCE for key changes, starting at %d: %s", maxOffset, err)
+		}
+	}
+
+	_, err := tx.ExecContext(ctx, `
+		-- make the new table
+		DROP TABLE IF EXISTS keyserver_key_changes;
+		CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+			change_id BIGINT PRIMARY KEY DEFAULT nextval('keyserver_key_changes_seq'),
+			user_id TEXT NOT NULL,
+			CONSTRAINT keyserver_key_changes_unique_per_user UNIQUE (user_id)
+		);
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	return nil
+}
+
+func DownRefactorKeyChanges(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `
+	-- Drop all data and revert back, we can't keep the data as Kafka offsets determine the numbers
+	DROP SEQUENCE IF EXISTS keyserver_key_changes_seq;
+	DROP TABLE IF EXISTS keyserver_key_changes;
+	CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+		partition BIGINT NOT NULL,
+		log_offset BIGINT NOT NULL,
+		user_id TEXT NOT NULL,
+		CONSTRAINT keyserver_key_changes_unique UNIQUE (partition, log_offset)
+	);
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute downgrade: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/storage/postgres/deltas/2022042612000000_xsigning_idx.go b/userapi/storage/postgres/deltas/2022042612000000_xsigning_idx.go
new file mode 100644
index 00000000..1a3d4fee
--- /dev/null
+++ b/userapi/storage/postgres/deltas/2022042612000000_xsigning_idx.go
@@ -0,0 +1,47 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package deltas
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+func UpFixCrossSigningSignatureIndexes(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `
+		ALTER TABLE keyserver_cross_signing_sigs DROP CONSTRAINT keyserver_cross_signing_sigs_pkey;
+		ALTER TABLE keyserver_cross_signing_sigs ADD PRIMARY KEY (origin_user_id, origin_key_id, target_user_id, target_key_id);
+
+		CREATE INDEX IF NOT EXISTS keyserver_cross_signing_sigs_idx ON keyserver_cross_signing_sigs (origin_user_id, target_user_id, target_key_id);
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	return nil
+}
+
+func DownFixCrossSigningSignatureIndexes(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `
+		ALTER TABLE keyserver_cross_signing_sigs DROP CONSTRAINT keyserver_cross_signing_sigs_pkey;
+		ALTER TABLE keyserver_cross_signing_sigs ADD PRIMARY KEY (origin_user_id, target_user_id, target_key_id);
+
+		DROP INDEX IF EXISTS keyserver_cross_signing_sigs_idx;
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute downgrade: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/storage/postgres/device_keys_table.go b/userapi/storage/postgres/device_keys_table.go
new file mode 100644
index 00000000..a9203857
--- /dev/null
+++ b/userapi/storage/postgres/device_keys_table.go
@@ -0,0 +1,213 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"time"
+
+	"github.com/lib/pq"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+)
+
+var deviceKeysSchema = `
+-- Stores device keys for users
+CREATE TABLE IF NOT EXISTS keyserver_device_keys (
+    user_id TEXT NOT NULL,
+	device_id TEXT NOT NULL,
+	ts_added_secs BIGINT NOT NULL,
+	key_json TEXT NOT NULL,
+	-- the stream ID of this key, scoped per-user. This gets updated when the device key changes.
+	-- This means we do not store an unbounded append-only log of device keys, which is not actually
+	-- required in the spec because in the event of a missed update the server fetches the entire
+	-- current set of keys rather than trying to 'fast-forward' or catchup missing stream IDs.
+	stream_id BIGINT NOT NULL,
+	display_name TEXT,
+	-- Clobber based on tuple of user/device.
+    CONSTRAINT keyserver_device_keys_unique UNIQUE (user_id, device_id)
+);
+`
+
+const upsertDeviceKeysSQL = "" +
+	"INSERT INTO keyserver_device_keys (user_id, device_id, ts_added_secs, key_json, stream_id, display_name)" +
+	" VALUES ($1, $2, $3, $4, $5, $6)" +
+	" ON CONFLICT ON CONSTRAINT keyserver_device_keys_unique" +
+	" DO UPDATE SET key_json = $4, stream_id = $5, display_name = $6"
+
+const selectDeviceKeysSQL = "" +
+	"SELECT key_json, stream_id, display_name FROM keyserver_device_keys WHERE user_id=$1 AND device_id=$2"
+
+const selectBatchDeviceKeysSQL = "" +
+	"SELECT device_id, key_json, stream_id, display_name FROM keyserver_device_keys WHERE user_id=$1 AND key_json <> ''"
+
+const selectBatchDeviceKeysWithEmptiesSQL = "" +
+	"SELECT device_id, key_json, stream_id, display_name FROM keyserver_device_keys WHERE user_id=$1"
+
+const selectMaxStreamForUserSQL = "" +
+	"SELECT MAX(stream_id) FROM keyserver_device_keys WHERE user_id=$1"
+
+const countStreamIDsForUserSQL = "" +
+	"SELECT COUNT(*) FROM keyserver_device_keys WHERE user_id=$1 AND stream_id = ANY($2)"
+
+const deleteDeviceKeysSQL = "" +
+	"DELETE FROM keyserver_device_keys WHERE user_id=$1 AND device_id=$2"
+
+const deleteAllDeviceKeysSQL = "" +
+	"DELETE FROM keyserver_device_keys WHERE user_id=$1"
+
+type deviceKeysStatements struct {
+	db                                   *sql.DB
+	upsertDeviceKeysStmt                 *sql.Stmt
+	selectDeviceKeysStmt                 *sql.Stmt
+	selectBatchDeviceKeysStmt            *sql.Stmt
+	selectBatchDeviceKeysWithEmptiesStmt *sql.Stmt
+	selectMaxStreamForUserStmt           *sql.Stmt
+	countStreamIDsForUserStmt            *sql.Stmt
+	deleteDeviceKeysStmt                 *sql.Stmt
+	deleteAllDeviceKeysStmt              *sql.Stmt
+}
+
+func NewPostgresDeviceKeysTable(db *sql.DB) (tables.DeviceKeys, error) {
+	s := &deviceKeysStatements{
+		db: db,
+	}
+	_, err := db.Exec(deviceKeysSchema)
+	if err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.upsertDeviceKeysStmt, upsertDeviceKeysSQL},
+		{&s.selectDeviceKeysStmt, selectDeviceKeysSQL},
+		{&s.selectBatchDeviceKeysStmt, selectBatchDeviceKeysSQL},
+		{&s.selectBatchDeviceKeysWithEmptiesStmt, selectBatchDeviceKeysWithEmptiesSQL},
+		{&s.selectMaxStreamForUserStmt, selectMaxStreamForUserSQL},
+		{&s.countStreamIDsForUserStmt, countStreamIDsForUserSQL},
+		{&s.deleteDeviceKeysStmt, deleteDeviceKeysSQL},
+		{&s.deleteAllDeviceKeysStmt, deleteAllDeviceKeysSQL},
+	}.Prepare(db)
+}
+
+func (s *deviceKeysStatements) SelectDeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error {
+	for i, key := range keys {
+		var keyJSONStr string
+		var streamID int64
+		var displayName sql.NullString
+		err := s.selectDeviceKeysStmt.QueryRowContext(ctx, key.UserID, key.DeviceID).Scan(&keyJSONStr, &streamID, &displayName)
+		if err != nil && err != sql.ErrNoRows {
+			return err
+		}
+		// this will be '' when there is no device
+		keys[i].Type = api.TypeDeviceKeyUpdate
+		keys[i].KeyJSON = []byte(keyJSONStr)
+		keys[i].StreamID = streamID
+		if displayName.Valid {
+			keys[i].DisplayName = displayName.String
+		}
+	}
+	return nil
+}
+
+func (s *deviceKeysStatements) SelectMaxStreamIDForUser(ctx context.Context, txn *sql.Tx, userID string) (streamID int64, err error) {
+	// nullable if there are no results
+	var nullStream sql.NullInt64
+	err = sqlutil.TxStmt(txn, s.selectMaxStreamForUserStmt).QueryRowContext(ctx, userID).Scan(&nullStream)
+	if err == sql.ErrNoRows {
+		err = nil
+	}
+	if nullStream.Valid {
+		streamID = nullStream.Int64
+	}
+	return
+}
+
+func (s *deviceKeysStatements) CountStreamIDsForUser(ctx context.Context, userID string, streamIDs []int64) (int, error) {
+	// nullable if there are no results
+	var count sql.NullInt32
+	err := s.countStreamIDsForUserStmt.QueryRowContext(ctx, userID, pq.Int64Array(streamIDs)).Scan(&count)
+	if err != nil {
+		return 0, err
+	}
+	if count.Valid {
+		return int(count.Int32), nil
+	}
+	return 0, nil
+}
+
+func (s *deviceKeysStatements) InsertDeviceKeys(ctx context.Context, txn *sql.Tx, keys []api.DeviceMessage) error {
+	for _, key := range keys {
+		now := time.Now().Unix()
+		_, err := sqlutil.TxStmt(txn, s.upsertDeviceKeysStmt).ExecContext(
+			ctx, key.UserID, key.DeviceID, now, string(key.KeyJSON), key.StreamID, key.DisplayName,
+		)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (s *deviceKeysStatements) DeleteDeviceKeys(ctx context.Context, txn *sql.Tx, userID, deviceID string) error {
+	_, err := sqlutil.TxStmt(txn, s.deleteDeviceKeysStmt).ExecContext(ctx, userID, deviceID)
+	return err
+}
+
+func (s *deviceKeysStatements) DeleteAllDeviceKeys(ctx context.Context, txn *sql.Tx, userID string) error {
+	_, err := sqlutil.TxStmt(txn, s.deleteAllDeviceKeysStmt).ExecContext(ctx, userID)
+	return err
+}
+
+func (s *deviceKeysStatements) SelectBatchDeviceKeys(ctx context.Context, userID string, deviceIDs []string, includeEmpty bool) ([]api.DeviceMessage, error) {
+	var stmt *sql.Stmt
+	if includeEmpty {
+		stmt = s.selectBatchDeviceKeysWithEmptiesStmt
+	} else {
+		stmt = s.selectBatchDeviceKeysStmt
+	}
+	rows, err := stmt.QueryContext(ctx, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectBatchDeviceKeysStmt: rows.close() failed")
+	deviceIDMap := make(map[string]bool)
+	for _, d := range deviceIDs {
+		deviceIDMap[d] = true
+	}
+	var result []api.DeviceMessage
+	var displayName sql.NullString
+	for rows.Next() {
+		dk := api.DeviceMessage{
+			Type: api.TypeDeviceKeyUpdate,
+			DeviceKeys: &api.DeviceKeys{
+				UserID: userID,
+			},
+		}
+		if err := rows.Scan(&dk.DeviceID, &dk.KeyJSON, &dk.StreamID, &displayName); err != nil {
+			return nil, err
+		}
+		if displayName.Valid {
+			dk.DisplayName = displayName.String
+		}
+		// include the key if we want all keys (no device) or it was asked
+		if deviceIDMap[dk.DeviceID] || len(deviceIDs) == 0 {
+			result = append(result, dk)
+		}
+	}
+	return result, rows.Err()
+}
diff --git a/userapi/storage/postgres/devices_table.go b/userapi/storage/postgres/devices_table.go
index 7481ac5b..88f8839c 100644
--- a/userapi/storage/postgres/devices_table.go
+++ b/userapi/storage/postgres/devices_table.go
@@ -160,7 +160,7 @@ func (s *devicesStatements) InsertDevice(
 	if err := stmt.QueryRowContext(ctx, id, localpart, serverName, accessToken, createdTimeMS, displayName, createdTimeMS, ipAddr, userAgent).Scan(&sessionID); err != nil {
 		return nil, fmt.Errorf("insertDeviceStmt: %w", err)
 	}
-	return &api.Device{
+	dev := &api.Device{
 		ID:          id,
 		UserID:      userutil.MakeUserID(localpart, serverName),
 		AccessToken: accessToken,
@@ -168,7 +168,11 @@ func (s *devicesStatements) InsertDevice(
 		LastSeenTS:  createdTimeMS,
 		LastSeenIP:  ipAddr,
 		UserAgent:   userAgent,
-	}, nil
+	}
+	if displayName != nil {
+		dev.DisplayName = *displayName
+	}
+	return dev, nil
 }
 
 func (s *devicesStatements) InsertDeviceWithSessionID(ctx context.Context, txn *sql.Tx, id,
diff --git a/userapi/storage/postgres/key_backup_table.go b/userapi/storage/postgres/key_backup_table.go
index 7b58f7ba..91a34c35 100644
--- a/userapi/storage/postgres/key_backup_table.go
+++ b/userapi/storage/postgres/key_backup_table.go
@@ -52,7 +52,7 @@ const updateBackupKeySQL = "" +
 const countKeysSQL = "" +
 	"SELECT COUNT(*) FROM userapi_key_backups WHERE user_id = $1 AND version = $2"
 
-const selectKeysSQL = "" +
+const selectBackupKeysSQL = "" +
 	"SELECT room_id, session_id, first_message_index, forwarded_count, is_verified, session_data FROM userapi_key_backups " +
 	"WHERE user_id = $1 AND version = $2"
 
@@ -83,7 +83,7 @@ func NewPostgresKeyBackupTable(db *sql.DB) (tables.KeyBackupTable, error) {
 		{&s.insertBackupKeyStmt, insertBackupKeySQL},
 		{&s.updateBackupKeyStmt, updateBackupKeySQL},
 		{&s.countKeysStmt, countKeysSQL},
-		{&s.selectKeysStmt, selectKeysSQL},
+		{&s.selectKeysStmt, selectBackupKeysSQL},
 		{&s.selectKeysByRoomIDStmt, selectKeysByRoomIDSQL},
 		{&s.selectKeysByRoomIDAndSessionIDStmt, selectKeysByRoomIDAndSessionIDSQL},
 	}.Prepare(db)
diff --git a/userapi/storage/postgres/key_changes_table.go b/userapi/storage/postgres/key_changes_table.go
new file mode 100644
index 00000000..a0049414
--- /dev/null
+++ b/userapi/storage/postgres/key_changes_table.go
@@ -0,0 +1,127 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/storage/postgres/deltas"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+)
+
+var keyChangesSchema = `
+-- Stores key change information about users. Used to determine when to send updated device lists to clients.
+CREATE SEQUENCE IF NOT EXISTS keyserver_key_changes_seq;
+CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+	change_id BIGINT PRIMARY KEY DEFAULT nextval('keyserver_key_changes_seq'),
+    user_id TEXT NOT NULL,
+    CONSTRAINT keyserver_key_changes_unique_per_user UNIQUE (user_id)
+);
+`
+
+// Replace based on user ID. We don't care how many times the user's keys have changed, only that they
+// have changed, hence we can just keep bumping the change ID for this user.
+const upsertKeyChangeSQL = "" +
+	"INSERT INTO keyserver_key_changes (user_id)" +
+	" VALUES ($1)" +
+	" ON CONFLICT ON CONSTRAINT keyserver_key_changes_unique_per_user" +
+	" DO UPDATE SET change_id = nextval('keyserver_key_changes_seq')" +
+	" RETURNING change_id"
+
+const selectKeyChangesSQL = "" +
+	"SELECT user_id, change_id FROM keyserver_key_changes WHERE change_id > $1 AND change_id <= $2"
+
+type keyChangesStatements struct {
+	db                   *sql.DB
+	upsertKeyChangeStmt  *sql.Stmt
+	selectKeyChangesStmt *sql.Stmt
+}
+
+func NewPostgresKeyChangesTable(db *sql.DB) (tables.KeyChanges, error) {
+	s := &keyChangesStatements{
+		db: db,
+	}
+	_, err := db.Exec(keyChangesSchema)
+	if err != nil {
+		return s, err
+	}
+
+	if err = executeMigration(context.Background(), db); err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.upsertKeyChangeStmt, upsertKeyChangeSQL},
+		{&s.selectKeyChangesStmt, selectKeyChangesSQL},
+	}.Prepare(db)
+}
+
+func executeMigration(ctx context.Context, db *sql.DB) error {
+	// TODO: Remove when we are sure we are not having goose artefacts in the db
+	// This forces an error, which indicates the migration is already applied, since the
+	// column partition was removed from the table
+	migrationName := "keyserver: refactor key changes"
+
+	var cName string
+	err := db.QueryRowContext(ctx, "select column_name from information_schema.columns where table_name = 'keyserver_key_changes' AND column_name = 'partition'").Scan(&cName)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) { // migration was already executed, as the column was removed
+			if err = sqlutil.InsertMigration(ctx, db, migrationName); err != nil {
+				return fmt.Errorf("unable to manually insert migration '%s': %w", migrationName, err)
+			}
+			return nil
+		}
+		return err
+	}
+	m := sqlutil.NewMigrator(db)
+	m.AddMigrations(sqlutil.Migration{
+		Version: migrationName,
+		Up:      deltas.UpRefactorKeyChanges,
+	})
+
+	return m.Up(ctx)
+}
+
+func (s *keyChangesStatements) InsertKeyChange(ctx context.Context, userID string) (changeID int64, err error) {
+	err = s.upsertKeyChangeStmt.QueryRowContext(ctx, userID).Scan(&changeID)
+	return
+}
+
+func (s *keyChangesStatements) SelectKeyChanges(
+	ctx context.Context, fromOffset, toOffset int64,
+) (userIDs []string, latestOffset int64, err error) {
+	latestOffset = fromOffset
+	rows, err := s.selectKeyChangesStmt.QueryContext(ctx, fromOffset, toOffset)
+	if err != nil {
+		return nil, 0, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeyChangesStmt: rows.close() failed")
+	for rows.Next() {
+		var userID string
+		var offset int64
+		if err := rows.Scan(&userID, &offset); err != nil {
+			return nil, 0, err
+		}
+		if offset > latestOffset {
+			latestOffset = offset
+		}
+		userIDs = append(userIDs, userID)
+	}
+	return
+}
diff --git a/userapi/storage/postgres/one_time_keys_table.go b/userapi/storage/postgres/one_time_keys_table.go
new file mode 100644
index 00000000..972a5914
--- /dev/null
+++ b/userapi/storage/postgres/one_time_keys_table.go
@@ -0,0 +1,194 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"time"
+
+	"github.com/lib/pq"
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+)
+
+var oneTimeKeysSchema = `
+-- Stores one-time public keys for users
+CREATE TABLE IF NOT EXISTS keyserver_one_time_keys (
+    user_id TEXT NOT NULL,
+	device_id TEXT NOT NULL,
+	key_id TEXT NOT NULL,
+	algorithm TEXT NOT NULL,
+	ts_added_secs BIGINT NOT NULL,
+	key_json TEXT NOT NULL,
+	-- Clobber based on 4-uple of user/device/key/algorithm.
+    CONSTRAINT keyserver_one_time_keys_unique UNIQUE (user_id, device_id, key_id, algorithm)
+);
+
+CREATE INDEX IF NOT EXISTS keyserver_one_time_keys_idx ON keyserver_one_time_keys (user_id, device_id);
+`
+
+const upsertKeysSQL = "" +
+	"INSERT INTO keyserver_one_time_keys (user_id, device_id, key_id, algorithm, ts_added_secs, key_json)" +
+	" VALUES ($1, $2, $3, $4, $5, $6)" +
+	" ON CONFLICT ON CONSTRAINT keyserver_one_time_keys_unique" +
+	" DO UPDATE SET key_json = $6"
+
+const selectOneTimeKeysSQL = "" +
+	"SELECT concat(algorithm, ':', key_id) as algorithmwithid, key_json FROM keyserver_one_time_keys WHERE user_id=$1 AND device_id=$2 AND concat(algorithm, ':', key_id) = ANY($3);"
+
+const selectKeysCountSQL = "" +
+	"SELECT algorithm, COUNT(key_id) FROM " +
+	" (SELECT algorithm, key_id FROM keyserver_one_time_keys WHERE user_id = $1 AND device_id = $2 LIMIT 100)" +
+	" x GROUP BY algorithm"
+
+const deleteOneTimeKeySQL = "" +
+	"DELETE FROM keyserver_one_time_keys WHERE user_id = $1 AND device_id = $2 AND algorithm = $3 AND key_id = $4"
+
+const selectKeyByAlgorithmSQL = "" +
+	"SELECT key_id, key_json FROM keyserver_one_time_keys WHERE user_id = $1 AND device_id = $2 AND algorithm = $3 LIMIT 1"
+
+const deleteOneTimeKeysSQL = "" +
+	"DELETE FROM keyserver_one_time_keys WHERE user_id = $1 AND device_id = $2"
+
+type oneTimeKeysStatements struct {
+	db                       *sql.DB
+	upsertKeysStmt           *sql.Stmt
+	selectKeysStmt           *sql.Stmt
+	selectKeysCountStmt      *sql.Stmt
+	selectKeyByAlgorithmStmt *sql.Stmt
+	deleteOneTimeKeyStmt     *sql.Stmt
+	deleteOneTimeKeysStmt    *sql.Stmt
+}
+
+func NewPostgresOneTimeKeysTable(db *sql.DB) (tables.OneTimeKeys, error) {
+	s := &oneTimeKeysStatements{
+		db: db,
+	}
+	_, err := db.Exec(oneTimeKeysSchema)
+	if err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.upsertKeysStmt, upsertKeysSQL},
+		{&s.selectKeysStmt, selectOneTimeKeysSQL},
+		{&s.selectKeysCountStmt, selectKeysCountSQL},
+		{&s.selectKeyByAlgorithmStmt, selectKeyByAlgorithmSQL},
+		{&s.deleteOneTimeKeyStmt, deleteOneTimeKeySQL},
+		{&s.deleteOneTimeKeysStmt, deleteOneTimeKeysSQL},
+	}.Prepare(db)
+}
+
+func (s *oneTimeKeysStatements) SelectOneTimeKeys(ctx context.Context, userID, deviceID string, keyIDsWithAlgorithms []string) (map[string]json.RawMessage, error) {
+	rows, err := s.selectKeysStmt.QueryContext(ctx, userID, deviceID, pq.Array(keyIDsWithAlgorithms))
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeysStmt: rows.close() failed")
+
+	result := make(map[string]json.RawMessage)
+	var (
+		algorithmWithID string
+		keyJSONStr      string
+	)
+	for rows.Next() {
+		if err := rows.Scan(&algorithmWithID, &keyJSONStr); err != nil {
+			return nil, err
+		}
+		result[algorithmWithID] = json.RawMessage(keyJSONStr)
+	}
+	return result, rows.Err()
+}
+
+func (s *oneTimeKeysStatements) CountOneTimeKeys(ctx context.Context, userID, deviceID string) (*api.OneTimeKeysCount, error) {
+	counts := &api.OneTimeKeysCount{
+		DeviceID: deviceID,
+		UserID:   userID,
+		KeyCount: make(map[string]int),
+	}
+	rows, err := s.selectKeysCountStmt.QueryContext(ctx, userID, deviceID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeysCountStmt: rows.close() failed")
+	for rows.Next() {
+		var algorithm string
+		var count int
+		if err = rows.Scan(&algorithm, &count); err != nil {
+			return nil, err
+		}
+		counts.KeyCount[algorithm] = count
+	}
+	return counts, nil
+}
+
+func (s *oneTimeKeysStatements) InsertOneTimeKeys(ctx context.Context, txn *sql.Tx, keys api.OneTimeKeys) (*api.OneTimeKeysCount, error) {
+	now := time.Now().Unix()
+	counts := &api.OneTimeKeysCount{
+		DeviceID: keys.DeviceID,
+		UserID:   keys.UserID,
+		KeyCount: make(map[string]int),
+	}
+	for keyIDWithAlgo, keyJSON := range keys.KeyJSON {
+		algo, keyID := keys.Split(keyIDWithAlgo)
+		_, err := sqlutil.TxStmt(txn, s.upsertKeysStmt).ExecContext(
+			ctx, keys.UserID, keys.DeviceID, keyID, algo, now, string(keyJSON),
+		)
+		if err != nil {
+			return nil, err
+		}
+	}
+	rows, err := sqlutil.TxStmt(txn, s.selectKeysCountStmt).QueryContext(ctx, keys.UserID, keys.DeviceID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeysCountStmt: rows.close() failed")
+	for rows.Next() {
+		var algorithm string
+		var count int
+		if err = rows.Scan(&algorithm, &count); err != nil {
+			return nil, err
+		}
+		counts.KeyCount[algorithm] = count
+	}
+
+	return counts, rows.Err()
+}
+
+func (s *oneTimeKeysStatements) SelectAndDeleteOneTimeKey(
+	ctx context.Context, txn *sql.Tx, userID, deviceID, algorithm string,
+) (map[string]json.RawMessage, error) {
+	var keyID string
+	var keyJSON string
+	err := sqlutil.TxStmtContext(ctx, txn, s.selectKeyByAlgorithmStmt).QueryRowContext(ctx, userID, deviceID, algorithm).Scan(&keyID, &keyJSON)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, err
+	}
+	_, err = sqlutil.TxStmtContext(ctx, txn, s.deleteOneTimeKeyStmt).ExecContext(ctx, userID, deviceID, algorithm, keyID)
+	return map[string]json.RawMessage{
+		algorithm + ":" + keyID: json.RawMessage(keyJSON),
+	}, err
+}
+
+func (s *oneTimeKeysStatements) DeleteOneTimeKeys(ctx context.Context, txn *sql.Tx, userID, deviceID string) error {
+	_, err := sqlutil.TxStmt(txn, s.deleteOneTimeKeysStmt).ExecContext(ctx, userID, deviceID)
+	return err
+}
diff --git a/userapi/storage/postgres/stale_device_lists.go b/userapi/storage/postgres/stale_device_lists.go
new file mode 100644
index 00000000..c823b58c
--- /dev/null
+++ b/userapi/storage/postgres/stale_device_lists.go
@@ -0,0 +1,131 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package postgres
+
+import (
+	"context"
+	"database/sql"
+	"time"
+
+	"github.com/lib/pq"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+var staleDeviceListsSchema = `
+-- Stores whether a user's device lists are stale or not.
+CREATE TABLE IF NOT EXISTS keyserver_stale_device_lists (
+    user_id TEXT PRIMARY KEY NOT NULL,
+	domain TEXT NOT NULL,
+	is_stale BOOLEAN NOT NULL,
+	ts_added_secs BIGINT NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS keyserver_stale_device_lists_idx ON keyserver_stale_device_lists (domain, is_stale);
+`
+
+const upsertStaleDeviceListSQL = "" +
+	"INSERT INTO keyserver_stale_device_lists (user_id, domain, is_stale, ts_added_secs)" +
+	" VALUES ($1, $2, $3, $4)" +
+	" ON CONFLICT (user_id)" +
+	" DO UPDATE SET is_stale = $3, ts_added_secs = $4"
+
+const selectStaleDeviceListsWithDomainsSQL = "" +
+	"SELECT user_id FROM keyserver_stale_device_lists WHERE is_stale = $1 AND domain = $2 ORDER BY ts_added_secs DESC"
+
+const selectStaleDeviceListsSQL = "" +
+	"SELECT user_id FROM keyserver_stale_device_lists WHERE is_stale = $1 ORDER BY ts_added_secs DESC"
+
+const deleteStaleDevicesSQL = "" +
+	"DELETE FROM keyserver_stale_device_lists WHERE user_id = ANY($1)"
+
+type staleDeviceListsStatements struct {
+	upsertStaleDeviceListStmt             *sql.Stmt
+	selectStaleDeviceListsWithDomainsStmt *sql.Stmt
+	selectStaleDeviceListsStmt            *sql.Stmt
+	deleteStaleDeviceListsStmt            *sql.Stmt
+}
+
+func NewPostgresStaleDeviceListsTable(db *sql.DB) (tables.StaleDeviceLists, error) {
+	s := &staleDeviceListsStatements{}
+	_, err := db.Exec(staleDeviceListsSchema)
+	if err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.upsertStaleDeviceListStmt, upsertStaleDeviceListSQL},
+		{&s.selectStaleDeviceListsStmt, selectStaleDeviceListsSQL},
+		{&s.selectStaleDeviceListsWithDomainsStmt, selectStaleDeviceListsWithDomainsSQL},
+		{&s.deleteStaleDeviceListsStmt, deleteStaleDevicesSQL},
+	}.Prepare(db)
+}
+
+func (s *staleDeviceListsStatements) InsertStaleDeviceList(ctx context.Context, userID string, isStale bool) error {
+	_, domain, err := gomatrixserverlib.SplitID('@', userID)
+	if err != nil {
+		return err
+	}
+	_, err = s.upsertStaleDeviceListStmt.ExecContext(ctx, userID, string(domain), isStale, gomatrixserverlib.AsTimestamp(time.Now()))
+	return err
+}
+
+func (s *staleDeviceListsStatements) SelectUserIDsWithStaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error) {
+	// we only query for 1 domain or all domains so optimise for those use cases
+	if len(domains) == 0 {
+		rows, err := s.selectStaleDeviceListsStmt.QueryContext(ctx, true)
+		if err != nil {
+			return nil, err
+		}
+		return rowsToUserIDs(ctx, rows)
+	}
+	var result []string
+	for _, domain := range domains {
+		rows, err := s.selectStaleDeviceListsWithDomainsStmt.QueryContext(ctx, true, string(domain))
+		if err != nil {
+			return nil, err
+		}
+		userIDs, err := rowsToUserIDs(ctx, rows)
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, userIDs...)
+	}
+	return result, nil
+}
+
+// DeleteStaleDeviceLists removes users from stale device lists
+func (s *staleDeviceListsStatements) DeleteStaleDeviceLists(
+	ctx context.Context, txn *sql.Tx, userIDs []string,
+) error {
+	stmt := sqlutil.TxStmt(txn, s.deleteStaleDeviceListsStmt)
+	_, err := stmt.ExecContext(ctx, pq.Array(userIDs))
+	return err
+}
+
+func rowsToUserIDs(ctx context.Context, rows *sql.Rows) (result []string, err error) {
+	defer internal.CloseAndLogIfError(ctx, rows, "closing rowsToUserIDs failed")
+	for rows.Next() {
+		var userID string
+		if err := rows.Scan(&userID); err != nil {
+			return nil, err
+		}
+		result = append(result, userID)
+	}
+	return result, rows.Err()
+}
diff --git a/userapi/storage/postgres/storage.go b/userapi/storage/postgres/storage.go
index 92dc4808..673d123b 100644
--- a/userapi/storage/postgres/storage.go
+++ b/userapi/storage/postgres/storage.go
@@ -136,3 +136,44 @@ func NewDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions,
 		OpenIDTokenLifetimeMS: openIDTokenLifetimeMS,
 	}, nil
 }
+
+func NewKeyDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions) (*shared.KeyDatabase, error) {
+	db, writer, err := base.DatabaseConnection(dbProperties, sqlutil.NewDummyWriter())
+	if err != nil {
+		return nil, err
+	}
+	otk, err := NewPostgresOneTimeKeysTable(db)
+	if err != nil {
+		return nil, err
+	}
+	dk, err := NewPostgresDeviceKeysTable(db)
+	if err != nil {
+		return nil, err
+	}
+	kc, err := NewPostgresKeyChangesTable(db)
+	if err != nil {
+		return nil, err
+	}
+	sdl, err := NewPostgresStaleDeviceListsTable(db)
+	if err != nil {
+		return nil, err
+	}
+	csk, err := NewPostgresCrossSigningKeysTable(db)
+	if err != nil {
+		return nil, err
+	}
+	css, err := NewPostgresCrossSigningSigsTable(db)
+	if err != nil {
+		return nil, err
+	}
+
+	return &shared.KeyDatabase{
+		OneTimeKeysTable:      otk,
+		DeviceKeysTable:       dk,
+		KeyChangesTable:       kc,
+		StaleDeviceListsTable: sdl,
+		CrossSigningKeysTable: csk,
+		CrossSigningSigsTable: css,
+		Writer:                writer,
+	}, nil
+}
diff --git a/userapi/storage/shared/storage.go b/userapi/storage/shared/storage.go
index bf94f14d..d3272a03 100644
--- a/userapi/storage/shared/storage.go
+++ b/userapi/storage/shared/storage.go
@@ -59,6 +59,17 @@ type Database struct {
 	OpenIDTokenLifetimeMS int64
 }
 
+type KeyDatabase struct {
+	OneTimeKeysTable      tables.OneTimeKeys
+	DeviceKeysTable       tables.DeviceKeys
+	KeyChangesTable       tables.KeyChanges
+	StaleDeviceListsTable tables.StaleDeviceLists
+	CrossSigningKeysTable tables.CrossSigningKeys
+	CrossSigningSigsTable tables.CrossSigningSigs
+	DB                    *sql.DB
+	Writer                sqlutil.Writer
+}
+
 const (
 	// The length of generated device IDs
 	deviceIDByteLength   = 6
@@ -875,3 +886,227 @@ func (d *Database) DailyRoomsMessages(
 ) (stats types.MessageStats, activeRooms, activeE2EERooms int64, err error) {
 	return d.Stats.DailyRoomsMessages(ctx, nil, serverName)
 }
+
+//
+
+func (d *KeyDatabase) ExistingOneTimeKeys(ctx context.Context, userID, deviceID string, keyIDsWithAlgorithms []string) (map[string]json.RawMessage, error) {
+	return d.OneTimeKeysTable.SelectOneTimeKeys(ctx, userID, deviceID, keyIDsWithAlgorithms)
+}
+
+func (d *KeyDatabase) StoreOneTimeKeys(ctx context.Context, keys api.OneTimeKeys) (counts *api.OneTimeKeysCount, err error) {
+	_ = d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		counts, err = d.OneTimeKeysTable.InsertOneTimeKeys(ctx, txn, keys)
+		return err
+	})
+	return
+}
+
+func (d *KeyDatabase) OneTimeKeysCount(ctx context.Context, userID, deviceID string) (*api.OneTimeKeysCount, error) {
+	return d.OneTimeKeysTable.CountOneTimeKeys(ctx, userID, deviceID)
+}
+
+func (d *KeyDatabase) DeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error {
+	return d.DeviceKeysTable.SelectDeviceKeysJSON(ctx, keys)
+}
+
+func (d *KeyDatabase) PrevIDsExists(ctx context.Context, userID string, prevIDs []int64) (bool, error) {
+	count, err := d.DeviceKeysTable.CountStreamIDsForUser(ctx, userID, prevIDs)
+	if err != nil {
+		return false, err
+	}
+	return count == len(prevIDs), nil
+}
+
+func (d *KeyDatabase) StoreRemoteDeviceKeys(ctx context.Context, keys []api.DeviceMessage, clearUserIDs []string) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		for _, userID := range clearUserIDs {
+			err := d.DeviceKeysTable.DeleteAllDeviceKeys(ctx, txn, userID)
+			if err != nil {
+				return err
+			}
+		}
+		return d.DeviceKeysTable.InsertDeviceKeys(ctx, txn, keys)
+	})
+}
+
+func (d *KeyDatabase) StoreLocalDeviceKeys(ctx context.Context, keys []api.DeviceMessage) error {
+	// work out the latest stream IDs for each user
+	userIDToStreamID := make(map[string]int64)
+	for _, k := range keys {
+		userIDToStreamID[k.UserID] = 0
+	}
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		for userID := range userIDToStreamID {
+			streamID, err := d.DeviceKeysTable.SelectMaxStreamIDForUser(ctx, txn, userID)
+			if err != nil {
+				return err
+			}
+			userIDToStreamID[userID] = streamID
+		}
+		// set the stream IDs for each key
+		for i := range keys {
+			k := keys[i]
+			userIDToStreamID[k.UserID]++ // start stream from 1
+			k.StreamID = userIDToStreamID[k.UserID]
+			keys[i] = k
+		}
+		return d.DeviceKeysTable.InsertDeviceKeys(ctx, txn, keys)
+	})
+}
+
+func (d *KeyDatabase) DeviceKeysForUser(ctx context.Context, userID string, deviceIDs []string, includeEmpty bool) ([]api.DeviceMessage, error) {
+	return d.DeviceKeysTable.SelectBatchDeviceKeys(ctx, userID, deviceIDs, includeEmpty)
+}
+
+func (d *KeyDatabase) ClaimKeys(ctx context.Context, userToDeviceToAlgorithm map[string]map[string]string) ([]api.OneTimeKeys, error) {
+	var result []api.OneTimeKeys
+	err := d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		for userID, deviceToAlgo := range userToDeviceToAlgorithm {
+			for deviceID, algo := range deviceToAlgo {
+				keyJSON, err := d.OneTimeKeysTable.SelectAndDeleteOneTimeKey(ctx, txn, userID, deviceID, algo)
+				if err != nil {
+					return err
+				}
+				if keyJSON != nil {
+					result = append(result, api.OneTimeKeys{
+						UserID:   userID,
+						DeviceID: deviceID,
+						KeyJSON:  keyJSON,
+					})
+				}
+			}
+		}
+		return nil
+	})
+	return result, err
+}
+
+func (d *KeyDatabase) StoreKeyChange(ctx context.Context, userID string) (id int64, err error) {
+	err = d.Writer.Do(nil, nil, func(_ *sql.Tx) error {
+		id, err = d.KeyChangesTable.InsertKeyChange(ctx, userID)
+		return err
+	})
+	return
+}
+
+func (d *KeyDatabase) KeyChanges(ctx context.Context, fromOffset, toOffset int64) (userIDs []string, latestOffset int64, err error) {
+	return d.KeyChangesTable.SelectKeyChanges(ctx, fromOffset, toOffset)
+}
+
+// StaleDeviceLists returns a list of user IDs ending with the domains provided who have stale device lists.
+// If no domains are given, all user IDs with stale device lists are returned.
+func (d *KeyDatabase) StaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error) {
+	return d.StaleDeviceListsTable.SelectUserIDsWithStaleDeviceLists(ctx, domains)
+}
+
+// MarkDeviceListStale sets the stale bit for this user to isStale.
+func (d *KeyDatabase) MarkDeviceListStale(ctx context.Context, userID string, isStale bool) error {
+	return d.Writer.Do(nil, nil, func(_ *sql.Tx) error {
+		return d.StaleDeviceListsTable.InsertStaleDeviceList(ctx, userID, isStale)
+	})
+}
+
+// DeleteDeviceKeys removes the device keys for a given user/device, and any accompanying
+// cross-signing signatures relating to that device.
+func (d *KeyDatabase) DeleteDeviceKeys(ctx context.Context, userID string, deviceIDs []gomatrixserverlib.KeyID) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		for _, deviceID := range deviceIDs {
+			if err := d.CrossSigningSigsTable.DeleteCrossSigningSigsForTarget(ctx, txn, userID, deviceID); err != nil && err != sql.ErrNoRows {
+				return fmt.Errorf("d.CrossSigningSigsTable.DeleteCrossSigningSigsForTarget: %w", err)
+			}
+			if err := d.DeviceKeysTable.DeleteDeviceKeys(ctx, txn, userID, string(deviceID)); err != nil && err != sql.ErrNoRows {
+				return fmt.Errorf("d.DeviceKeysTable.DeleteDeviceKeys: %w", err)
+			}
+			if err := d.OneTimeKeysTable.DeleteOneTimeKeys(ctx, txn, userID, string(deviceID)); err != nil && err != sql.ErrNoRows {
+				return fmt.Errorf("d.OneTimeKeysTable.DeleteOneTimeKeys: %w", err)
+			}
+		}
+		return nil
+	})
+}
+
+// CrossSigningKeysForUser returns the latest known cross-signing keys for a user, if any.
+func (d *KeyDatabase) CrossSigningKeysForUser(ctx context.Context, userID string) (map[gomatrixserverlib.CrossSigningKeyPurpose]gomatrixserverlib.CrossSigningKey, error) {
+	keyMap, err := d.CrossSigningKeysTable.SelectCrossSigningKeysForUser(ctx, nil, userID)
+	if err != nil {
+		return nil, fmt.Errorf("d.CrossSigningKeysTable.SelectCrossSigningKeysForUser: %w", err)
+	}
+	results := map[gomatrixserverlib.CrossSigningKeyPurpose]gomatrixserverlib.CrossSigningKey{}
+	for purpose, key := range keyMap {
+		keyID := gomatrixserverlib.KeyID("ed25519:" + key.Encode())
+		result := gomatrixserverlib.CrossSigningKey{
+			UserID: userID,
+			Usage:  []gomatrixserverlib.CrossSigningKeyPurpose{purpose},
+			Keys: map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{
+				keyID: key,
+			},
+		}
+		sigMap, err := d.CrossSigningSigsTable.SelectCrossSigningSigsForTarget(ctx, nil, userID, userID, keyID)
+		if err != nil {
+			continue
+		}
+		for sigUserID, forSigUserID := range sigMap {
+			if userID != sigUserID {
+				continue
+			}
+			if result.Signatures == nil {
+				result.Signatures = map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+			}
+			if _, ok := result.Signatures[sigUserID]; !ok {
+				result.Signatures[sigUserID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+			}
+			for sigKeyID, sigBytes := range forSigUserID {
+				result.Signatures[sigUserID][sigKeyID] = sigBytes
+			}
+		}
+		results[purpose] = result
+	}
+	return results, nil
+}
+
+// CrossSigningKeysForUser returns the latest known cross-signing keys for a user, if any.
+func (d *KeyDatabase) CrossSigningKeysDataForUser(ctx context.Context, userID string) (types.CrossSigningKeyMap, error) {
+	return d.CrossSigningKeysTable.SelectCrossSigningKeysForUser(ctx, nil, userID)
+}
+
+// CrossSigningSigsForTarget returns the signatures for a given user's key ID, if any.
+func (d *KeyDatabase) CrossSigningSigsForTarget(ctx context.Context, originUserID, targetUserID string, targetKeyID gomatrixserverlib.KeyID) (types.CrossSigningSigMap, error) {
+	return d.CrossSigningSigsTable.SelectCrossSigningSigsForTarget(ctx, nil, originUserID, targetUserID, targetKeyID)
+}
+
+// StoreCrossSigningKeysForUser stores the latest known cross-signing keys for a user.
+func (d *KeyDatabase) StoreCrossSigningKeysForUser(ctx context.Context, userID string, keyMap types.CrossSigningKeyMap) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		for keyType, keyData := range keyMap {
+			if err := d.CrossSigningKeysTable.UpsertCrossSigningKeysForUser(ctx, txn, userID, keyType, keyData); err != nil {
+				return fmt.Errorf("d.CrossSigningKeysTable.InsertCrossSigningKeysForUser: %w", err)
+			}
+		}
+		return nil
+	})
+}
+
+// StoreCrossSigningSigsForTarget stores a signature for a target user ID and key/dvice.
+func (d *KeyDatabase) StoreCrossSigningSigsForTarget(
+	ctx context.Context,
+	originUserID string, originKeyID gomatrixserverlib.KeyID,
+	targetUserID string, targetKeyID gomatrixserverlib.KeyID,
+	signature gomatrixserverlib.Base64Bytes,
+) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		if err := d.CrossSigningSigsTable.UpsertCrossSigningSigsForTarget(ctx, nil, originUserID, originKeyID, targetUserID, targetKeyID, signature); err != nil {
+			return fmt.Errorf("d.CrossSigningSigsTable.InsertCrossSigningSigsForTarget: %w", err)
+		}
+		return nil
+	})
+}
+
+// DeleteStaleDeviceLists deletes stale device list entries for users we don't share a room with anymore.
+func (d *KeyDatabase) DeleteStaleDeviceLists(
+	ctx context.Context,
+	userIDs []string,
+) error {
+	return d.Writer.Do(d.DB, nil, func(txn *sql.Tx) error {
+		return d.StaleDeviceListsTable.DeleteStaleDeviceLists(ctx, txn, userIDs)
+	})
+}
diff --git a/userapi/storage/sqlite3/cross_signing_keys_table.go b/userapi/storage/sqlite3/cross_signing_keys_table.go
new file mode 100644
index 00000000..10721fcc
--- /dev/null
+++ b/userapi/storage/sqlite3/cross_signing_keys_table.go
@@ -0,0 +1,101 @@
+// Copyright 2021 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+	"github.com/matrix-org/dendrite/userapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+var crossSigningKeysSchema = `
+CREATE TABLE IF NOT EXISTS keyserver_cross_signing_keys (
+    user_id TEXT NOT NULL,
+	key_type INTEGER NOT NULL,
+	key_data TEXT NOT NULL,
+	PRIMARY KEY (user_id, key_type)
+);
+`
+
+const selectCrossSigningKeysForUserSQL = "" +
+	"SELECT key_type, key_data FROM keyserver_cross_signing_keys" +
+	" WHERE user_id = $1"
+
+const upsertCrossSigningKeysForUserSQL = "" +
+	"INSERT OR REPLACE INTO keyserver_cross_signing_keys (user_id, key_type, key_data)" +
+	" VALUES($1, $2, $3)"
+
+type crossSigningKeysStatements struct {
+	db                                *sql.DB
+	selectCrossSigningKeysForUserStmt *sql.Stmt
+	upsertCrossSigningKeysForUserStmt *sql.Stmt
+}
+
+func NewSqliteCrossSigningKeysTable(db *sql.DB) (tables.CrossSigningKeys, error) {
+	s := &crossSigningKeysStatements{
+		db: db,
+	}
+	_, err := db.Exec(crossSigningKeysSchema)
+	if err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.selectCrossSigningKeysForUserStmt, selectCrossSigningKeysForUserSQL},
+		{&s.upsertCrossSigningKeysForUserStmt, upsertCrossSigningKeysForUserSQL},
+	}.Prepare(db)
+}
+
+func (s *crossSigningKeysStatements) SelectCrossSigningKeysForUser(
+	ctx context.Context, txn *sql.Tx, userID string,
+) (r types.CrossSigningKeyMap, err error) {
+	rows, err := sqlutil.TxStmt(txn, s.selectCrossSigningKeysForUserStmt).QueryContext(ctx, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectCrossSigningKeysForUserStmt: rows.close() failed")
+	r = types.CrossSigningKeyMap{}
+	for rows.Next() {
+		var keyTypeInt int16
+		var keyData gomatrixserverlib.Base64Bytes
+		if err := rows.Scan(&keyTypeInt, &keyData); err != nil {
+			return nil, err
+		}
+		keyType, ok := types.KeyTypeIntToPurpose[keyTypeInt]
+		if !ok {
+			return nil, fmt.Errorf("unknown key purpose int %d", keyTypeInt)
+		}
+		r[keyType] = keyData
+	}
+	return
+}
+
+func (s *crossSigningKeysStatements) UpsertCrossSigningKeysForUser(
+	ctx context.Context, txn *sql.Tx, userID string, keyType gomatrixserverlib.CrossSigningKeyPurpose, keyData gomatrixserverlib.Base64Bytes,
+) error {
+	keyTypeInt, ok := types.KeyTypePurposeToInt[keyType]
+	if !ok {
+		return fmt.Errorf("unknown key purpose %q", keyType)
+	}
+	if _, err := sqlutil.TxStmt(txn, s.upsertCrossSigningKeysForUserStmt).ExecContext(ctx, userID, keyTypeInt, keyData); err != nil {
+		return fmt.Errorf("s.upsertCrossSigningKeysForUserStmt: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/storage/sqlite3/cross_signing_sigs_table.go b/userapi/storage/sqlite3/cross_signing_sigs_table.go
new file mode 100644
index 00000000..2be00c9c
--- /dev/null
+++ b/userapi/storage/sqlite3/cross_signing_sigs_table.go
@@ -0,0 +1,129 @@
+// Copyright 2021 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/storage/sqlite3/deltas"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+	"github.com/matrix-org/dendrite/userapi/types"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+var crossSigningSigsSchema = `
+CREATE TABLE IF NOT EXISTS keyserver_cross_signing_sigs (
+    origin_user_id TEXT NOT NULL,
+	origin_key_id TEXT NOT NULL,
+	target_user_id TEXT NOT NULL,
+	target_key_id TEXT NOT NULL,
+	signature TEXT NOT NULL,
+	PRIMARY KEY (origin_user_id, origin_key_id, target_user_id, target_key_id)
+);
+
+CREATE INDEX IF NOT EXISTS keyserver_cross_signing_sigs_idx ON keyserver_cross_signing_sigs (origin_user_id, target_user_id, target_key_id);
+`
+
+const selectCrossSigningSigsForTargetSQL = "" +
+	"SELECT origin_user_id, origin_key_id, signature FROM keyserver_cross_signing_sigs" +
+	" WHERE (origin_user_id = $1 OR origin_user_id = $2) AND target_user_id = $3 AND target_key_id = $4"
+
+const upsertCrossSigningSigsForTargetSQL = "" +
+	"INSERT OR REPLACE INTO keyserver_cross_signing_sigs (origin_user_id, origin_key_id, target_user_id, target_key_id, signature)" +
+	" VALUES($1, $2, $3, $4, $5)"
+
+const deleteCrossSigningSigsForTargetSQL = "" +
+	"DELETE FROM keyserver_cross_signing_sigs WHERE target_user_id=$1 AND target_key_id=$2"
+
+type crossSigningSigsStatements struct {
+	db                                  *sql.DB
+	selectCrossSigningSigsForTargetStmt *sql.Stmt
+	upsertCrossSigningSigsForTargetStmt *sql.Stmt
+	deleteCrossSigningSigsForTargetStmt *sql.Stmt
+}
+
+func NewSqliteCrossSigningSigsTable(db *sql.DB) (tables.CrossSigningSigs, error) {
+	s := &crossSigningSigsStatements{
+		db: db,
+	}
+	_, err := db.Exec(crossSigningSigsSchema)
+	if err != nil {
+		return nil, err
+	}
+	m := sqlutil.NewMigrator(db)
+	m.AddMigrations(sqlutil.Migration{
+		Version: "keyserver: cross signing signature indexes",
+		Up:      deltas.UpFixCrossSigningSignatureIndexes,
+	})
+	if err = m.Up(context.Background()); err != nil {
+		return nil, err
+	}
+
+	return s, sqlutil.StatementList{
+		{&s.selectCrossSigningSigsForTargetStmt, selectCrossSigningSigsForTargetSQL},
+		{&s.upsertCrossSigningSigsForTargetStmt, upsertCrossSigningSigsForTargetSQL},
+		{&s.deleteCrossSigningSigsForTargetStmt, deleteCrossSigningSigsForTargetSQL},
+	}.Prepare(db)
+}
+
+func (s *crossSigningSigsStatements) SelectCrossSigningSigsForTarget(
+	ctx context.Context, txn *sql.Tx, originUserID, targetUserID string, targetKeyID gomatrixserverlib.KeyID,
+) (r types.CrossSigningSigMap, err error) {
+	rows, err := sqlutil.TxStmt(txn, s.selectCrossSigningSigsForTargetStmt).QueryContext(ctx, originUserID, targetUserID, targetUserID, targetKeyID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectCrossSigningSigsForOriginTargetStmt: rows.close() failed")
+	r = types.CrossSigningSigMap{}
+	for rows.Next() {
+		var userID string
+		var keyID gomatrixserverlib.KeyID
+		var signature gomatrixserverlib.Base64Bytes
+		if err := rows.Scan(&userID, &keyID, &signature); err != nil {
+			return nil, err
+		}
+		if _, ok := r[userID]; !ok {
+			r[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{}
+		}
+		r[userID][keyID] = signature
+	}
+	return
+}
+
+func (s *crossSigningSigsStatements) UpsertCrossSigningSigsForTarget(
+	ctx context.Context, txn *sql.Tx,
+	originUserID string, originKeyID gomatrixserverlib.KeyID,
+	targetUserID string, targetKeyID gomatrixserverlib.KeyID,
+	signature gomatrixserverlib.Base64Bytes,
+) error {
+	if _, err := sqlutil.TxStmt(txn, s.upsertCrossSigningSigsForTargetStmt).ExecContext(ctx, originUserID, originKeyID, targetUserID, targetKeyID, signature); err != nil {
+		return fmt.Errorf("s.upsertCrossSigningSigsForTargetStmt: %w", err)
+	}
+	return nil
+}
+
+func (s *crossSigningSigsStatements) DeleteCrossSigningSigsForTarget(
+	ctx context.Context, txn *sql.Tx,
+	targetUserID string, targetKeyID gomatrixserverlib.KeyID,
+) error {
+	if _, err := sqlutil.TxStmt(txn, s.deleteCrossSigningSigsForTargetStmt).ExecContext(ctx, targetUserID, targetKeyID); err != nil {
+		return fmt.Errorf("s.deleteCrossSigningSigsForTargetStmt: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/storage/sqlite3/deltas/2022012016470000_key_changes.go b/userapi/storage/sqlite3/deltas/2022012016470000_key_changes.go
new file mode 100644
index 00000000..cd0f19df
--- /dev/null
+++ b/userapi/storage/sqlite3/deltas/2022012016470000_key_changes.go
@@ -0,0 +1,66 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package deltas
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+func UpRefactorKeyChanges(ctx context.Context, tx *sql.Tx) error {
+	// start counting from the last max offset, else 0.
+	var maxOffset int64
+	var userID string
+	_ = tx.QueryRowContext(ctx, `SELECT user_id, MAX(log_offset) FROM keyserver_key_changes GROUP BY user_id`).Scan(&userID, &maxOffset)
+
+	_, err := tx.ExecContext(ctx, `
+		-- make the new table
+		DROP TABLE IF EXISTS keyserver_key_changes;
+		CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+			change_id INTEGER PRIMARY KEY AUTOINCREMENT,
+			-- The key owner
+			user_id TEXT NOT NULL,
+			UNIQUE (user_id)
+		);
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	// to start counting from maxOffset, insert a row with that value
+	if userID != "" {
+		_, err = tx.ExecContext(ctx, `INSERT INTO keyserver_key_changes(change_id, user_id) VALUES($1, $2)`, maxOffset, userID)
+		return err
+	}
+	return nil
+}
+
+func DownRefactorKeyChanges(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `
+	-- Drop all data and revert back, we can't keep the data as Kafka offsets determine the numbers
+	DROP TABLE IF EXISTS keyserver_key_changes;
+	CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+		partition BIGINT NOT NULL,
+		offset BIGINT NOT NULL,
+		-- The key owner
+		user_id TEXT NOT NULL,
+		UNIQUE (partition, offset)
+	);
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute downgrade: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/storage/sqlite3/deltas/2022042612000000_xsigning_idx.go b/userapi/storage/sqlite3/deltas/2022042612000000_xsigning_idx.go
new file mode 100644
index 00000000..d4e38dea
--- /dev/null
+++ b/userapi/storage/sqlite3/deltas/2022042612000000_xsigning_idx.go
@@ -0,0 +1,71 @@
+// Copyright 2022 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package deltas
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+)
+
+func UpFixCrossSigningSignatureIndexes(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `
+		CREATE TABLE IF NOT EXISTS keyserver_cross_signing_sigs_tmp (
+			origin_user_id TEXT NOT NULL,
+			origin_key_id TEXT NOT NULL,
+			target_user_id TEXT NOT NULL,
+			target_key_id TEXT NOT NULL,
+			signature TEXT NOT NULL,
+			PRIMARY KEY (origin_user_id, origin_key_id, target_user_id, target_key_id)
+		);
+
+		INSERT INTO keyserver_cross_signing_sigs_tmp (origin_user_id, origin_key_id, target_user_id, target_key_id, signature)
+			SELECT origin_user_id, origin_key_id, target_user_id, target_key_id, signature FROM keyserver_cross_signing_sigs;
+
+		DROP TABLE keyserver_cross_signing_sigs;
+		ALTER TABLE keyserver_cross_signing_sigs_tmp RENAME TO keyserver_cross_signing_sigs;
+
+		CREATE INDEX IF NOT EXISTS keyserver_cross_signing_sigs_idx ON keyserver_cross_signing_sigs (origin_user_id, target_user_id, target_key_id);
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute upgrade: %w", err)
+	}
+	return nil
+}
+
+func DownFixCrossSigningSignatureIndexes(ctx context.Context, tx *sql.Tx) error {
+	_, err := tx.ExecContext(ctx, `
+		CREATE TABLE IF NOT EXISTS keyserver_cross_signing_sigs_tmp (
+			origin_user_id TEXT NOT NULL,
+			origin_key_id TEXT NOT NULL,
+			target_user_id TEXT NOT NULL,
+			target_key_id TEXT NOT NULL,
+			signature TEXT NOT NULL,
+			PRIMARY KEY (origin_user_id, target_user_id, target_key_id)
+		);
+
+		INSERT INTO keyserver_cross_signing_sigs_tmp (origin_user_id, origin_key_id, target_user_id, target_key_id, signature)
+			SELECT origin_user_id, origin_key_id, target_user_id, target_key_id, signature FROM keyserver_cross_signing_sigs;
+
+		DROP TABLE keyserver_cross_signing_sigs;
+		ALTER TABLE keyserver_cross_signing_sigs_tmp RENAME TO keyserver_cross_signing_sigs;
+		
+		DELETE INDEX IF EXISTS keyserver_cross_signing_sigs_idx;
+	`)
+	if err != nil {
+		return fmt.Errorf("failed to execute downgrade: %w", err)
+	}
+	return nil
+}
diff --git a/userapi/storage/sqlite3/device_keys_table.go b/userapi/storage/sqlite3/device_keys_table.go
new file mode 100644
index 00000000..15e69cc4
--- /dev/null
+++ b/userapi/storage/sqlite3/device_keys_table.go
@@ -0,0 +1,213 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"strings"
+	"time"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+)
+
+var deviceKeysSchema = `
+-- Stores device keys for users
+CREATE TABLE IF NOT EXISTS keyserver_device_keys (
+    user_id TEXT NOT NULL,
+	device_id TEXT NOT NULL,
+	ts_added_secs BIGINT NOT NULL,
+	key_json TEXT NOT NULL,
+	stream_id BIGINT NOT NULL,
+	display_name TEXT,
+	-- Clobber based on tuple of user/device.
+    UNIQUE (user_id, device_id)
+);
+`
+
+const upsertDeviceKeysSQL = "" +
+	"INSERT INTO keyserver_device_keys (user_id, device_id, ts_added_secs, key_json, stream_id, display_name)" +
+	" VALUES ($1, $2, $3, $4, $5, $6)" +
+	" ON CONFLICT (user_id, device_id)" +
+	" DO UPDATE SET key_json = $4, stream_id = $5, display_name = $6"
+
+const selectDeviceKeysSQL = "" +
+	"SELECT key_json, stream_id, display_name FROM keyserver_device_keys WHERE user_id=$1 AND device_id=$2"
+
+const selectBatchDeviceKeysSQL = "" +
+	"SELECT device_id, key_json, stream_id, display_name FROM keyserver_device_keys WHERE user_id=$1 AND key_json <> ''"
+
+const selectBatchDeviceKeysWithEmptiesSQL = "" +
+	"SELECT device_id, key_json, stream_id, display_name FROM keyserver_device_keys WHERE user_id=$1"
+
+const selectMaxStreamForUserSQL = "" +
+	"SELECT MAX(stream_id) FROM keyserver_device_keys WHERE user_id=$1"
+
+const countStreamIDsForUserSQL = "" +
+	"SELECT COUNT(*) FROM keyserver_device_keys WHERE user_id=$1 AND stream_id IN ($2)"
+
+const deleteDeviceKeysSQL = "" +
+	"DELETE FROM keyserver_device_keys WHERE user_id=$1 AND device_id=$2"
+
+const deleteAllDeviceKeysSQL = "" +
+	"DELETE FROM keyserver_device_keys WHERE user_id=$1"
+
+type deviceKeysStatements struct {
+	db                                   *sql.DB
+	upsertDeviceKeysStmt                 *sql.Stmt
+	selectDeviceKeysStmt                 *sql.Stmt
+	selectBatchDeviceKeysStmt            *sql.Stmt
+	selectBatchDeviceKeysWithEmptiesStmt *sql.Stmt
+	selectMaxStreamForUserStmt           *sql.Stmt
+	deleteDeviceKeysStmt                 *sql.Stmt
+	deleteAllDeviceKeysStmt              *sql.Stmt
+}
+
+func NewSqliteDeviceKeysTable(db *sql.DB) (tables.DeviceKeys, error) {
+	s := &deviceKeysStatements{
+		db: db,
+	}
+	_, err := db.Exec(deviceKeysSchema)
+	if err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.upsertDeviceKeysStmt, upsertDeviceKeysSQL},
+		{&s.selectDeviceKeysStmt, selectDeviceKeysSQL},
+		{&s.selectBatchDeviceKeysStmt, selectBatchDeviceKeysSQL},
+		{&s.selectBatchDeviceKeysWithEmptiesStmt, selectBatchDeviceKeysWithEmptiesSQL},
+		{&s.selectMaxStreamForUserStmt, selectMaxStreamForUserSQL},
+		// {&s.countStreamIDsForUserStmt, countStreamIDsForUserSQL}, // prepared at runtime
+		{&s.deleteDeviceKeysStmt, deleteDeviceKeysSQL},
+		{&s.deleteAllDeviceKeysStmt, deleteAllDeviceKeysSQL},
+	}.Prepare(db)
+}
+
+func (s *deviceKeysStatements) DeleteDeviceKeys(ctx context.Context, txn *sql.Tx, userID, deviceID string) error {
+	_, err := sqlutil.TxStmt(txn, s.deleteDeviceKeysStmt).ExecContext(ctx, userID, deviceID)
+	return err
+}
+
+func (s *deviceKeysStatements) DeleteAllDeviceKeys(ctx context.Context, txn *sql.Tx, userID string) error {
+	_, err := sqlutil.TxStmt(txn, s.deleteAllDeviceKeysStmt).ExecContext(ctx, userID)
+	return err
+}
+
+func (s *deviceKeysStatements) SelectBatchDeviceKeys(ctx context.Context, userID string, deviceIDs []string, includeEmpty bool) ([]api.DeviceMessage, error) {
+	deviceIDMap := make(map[string]bool)
+	for _, d := range deviceIDs {
+		deviceIDMap[d] = true
+	}
+	var stmt *sql.Stmt
+	if includeEmpty {
+		stmt = s.selectBatchDeviceKeysWithEmptiesStmt
+	} else {
+		stmt = s.selectBatchDeviceKeysStmt
+	}
+	rows, err := stmt.QueryContext(ctx, userID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectBatchDeviceKeysStmt: rows.close() failed")
+	var result []api.DeviceMessage
+	var displayName sql.NullString
+	for rows.Next() {
+		dk := api.DeviceMessage{
+			Type: api.TypeDeviceKeyUpdate,
+			DeviceKeys: &api.DeviceKeys{
+				UserID: userID,
+			},
+		}
+		if err := rows.Scan(&dk.DeviceID, &dk.KeyJSON, &dk.StreamID, &displayName); err != nil {
+			return nil, err
+		}
+		if displayName.Valid {
+			dk.DisplayName = displayName.String
+		}
+		// include the key if we want all keys (no device) or it was asked
+		if deviceIDMap[dk.DeviceID] || len(deviceIDs) == 0 {
+			result = append(result, dk)
+		}
+	}
+	return result, rows.Err()
+}
+
+func (s *deviceKeysStatements) SelectDeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error {
+	for i, key := range keys {
+		var keyJSONStr string
+		var streamID int64
+		var displayName sql.NullString
+		err := s.selectDeviceKeysStmt.QueryRowContext(ctx, key.UserID, key.DeviceID).Scan(&keyJSONStr, &streamID, &displayName)
+		if err != nil && err != sql.ErrNoRows {
+			return err
+		}
+		// this will be '' when there is no device
+		keys[i].Type = api.TypeDeviceKeyUpdate
+		keys[i].KeyJSON = []byte(keyJSONStr)
+		keys[i].StreamID = streamID
+		if displayName.Valid {
+			keys[i].DisplayName = displayName.String
+		}
+	}
+	return nil
+}
+
+func (s *deviceKeysStatements) SelectMaxStreamIDForUser(ctx context.Context, txn *sql.Tx, userID string) (streamID int64, err error) {
+	// nullable if there are no results
+	var nullStream sql.NullInt64
+	err = sqlutil.TxStmt(txn, s.selectMaxStreamForUserStmt).QueryRowContext(ctx, userID).Scan(&nullStream)
+	if err == sql.ErrNoRows {
+		err = nil
+	}
+	if nullStream.Valid {
+		streamID = nullStream.Int64
+	}
+	return
+}
+
+func (s *deviceKeysStatements) CountStreamIDsForUser(ctx context.Context, userID string, streamIDs []int64) (int, error) {
+	iStreamIDs := make([]interface{}, len(streamIDs)+1)
+	iStreamIDs[0] = userID
+	for i := range streamIDs {
+		iStreamIDs[i+1] = streamIDs[i]
+	}
+	query := strings.Replace(countStreamIDsForUserSQL, "($2)", sqlutil.QueryVariadicOffset(len(streamIDs), 1), 1)
+	// nullable if there are no results
+	var count sql.NullInt64
+	err := s.db.QueryRowContext(ctx, query, iStreamIDs...).Scan(&count)
+	if err != nil {
+		return 0, err
+	}
+	if count.Valid {
+		return int(count.Int64), nil
+	}
+	return 0, nil
+}
+
+func (s *deviceKeysStatements) InsertDeviceKeys(ctx context.Context, txn *sql.Tx, keys []api.DeviceMessage) error {
+	for _, key := range keys {
+		now := time.Now().Unix()
+		_, err := sqlutil.TxStmt(txn, s.upsertDeviceKeysStmt).ExecContext(
+			ctx, key.UserID, key.DeviceID, now, string(key.KeyJSON), key.StreamID, key.DisplayName,
+		)
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
diff --git a/userapi/storage/sqlite3/devices_table.go b/userapi/storage/sqlite3/devices_table.go
index 449e4549..65e17527 100644
--- a/userapi/storage/sqlite3/devices_table.go
+++ b/userapi/storage/sqlite3/devices_table.go
@@ -151,7 +151,7 @@ func (s *devicesStatements) InsertDevice(
 	if _, err := insertStmt.ExecContext(ctx, id, localpart, serverName, accessToken, createdTimeMS, displayName, sessionID, createdTimeMS, ipAddr, userAgent); err != nil {
 		return nil, err
 	}
-	return &api.Device{
+	dev := &api.Device{
 		ID:          id,
 		UserID:      userutil.MakeUserID(localpart, serverName),
 		AccessToken: accessToken,
@@ -159,7 +159,11 @@ func (s *devicesStatements) InsertDevice(
 		LastSeenTS:  createdTimeMS,
 		LastSeenIP:  ipAddr,
 		UserAgent:   userAgent,
-	}, nil
+	}
+	if displayName != nil {
+		dev.DisplayName = *displayName
+	}
+	return dev, nil
 }
 
 func (s *devicesStatements) InsertDeviceWithSessionID(ctx context.Context, txn *sql.Tx, id,
@@ -172,7 +176,7 @@ func (s *devicesStatements) InsertDeviceWithSessionID(ctx context.Context, txn *
 	if _, err := insertStmt.ExecContext(ctx, id, localpart, serverName, accessToken, createdTimeMS, displayName, sessionID, createdTimeMS, ipAddr, userAgent); err != nil {
 		return nil, err
 	}
-	return &api.Device{
+	dev := &api.Device{
 		ID:          id,
 		UserID:      userutil.MakeUserID(localpart, serverName),
 		AccessToken: accessToken,
@@ -180,7 +184,11 @@ func (s *devicesStatements) InsertDeviceWithSessionID(ctx context.Context, txn *
 		LastSeenTS:  createdTimeMS,
 		LastSeenIP:  ipAddr,
 		UserAgent:   userAgent,
-	}, nil
+	}
+	if displayName != nil {
+		dev.DisplayName = *displayName
+	}
+	return dev, nil
 }
 
 func (s *devicesStatements) DeleteDevice(
@@ -202,6 +210,7 @@ func (s *devicesStatements) DeleteDevices(
 	if err != nil {
 		return err
 	}
+	defer internal.CloseAndLogIfError(ctx, prep, "DeleteDevices.StmtClose() failed")
 	stmt := sqlutil.TxStmt(txn, prep)
 	params := make([]interface{}, len(devices)+2)
 	params[0] = localpart
diff --git a/userapi/storage/sqlite3/key_backup_table.go b/userapi/storage/sqlite3/key_backup_table.go
index 7883ffb1..ed274631 100644
--- a/userapi/storage/sqlite3/key_backup_table.go
+++ b/userapi/storage/sqlite3/key_backup_table.go
@@ -52,7 +52,7 @@ const updateBackupKeySQL = "" +
 const countKeysSQL = "" +
 	"SELECT COUNT(*) FROM userapi_key_backups WHERE user_id = $1 AND version = $2"
 
-const selectKeysSQL = "" +
+const selectBackupKeysSQL = "" +
 	"SELECT room_id, session_id, first_message_index, forwarded_count, is_verified, session_data FROM userapi_key_backups " +
 	"WHERE user_id = $1 AND version = $2"
 
@@ -83,7 +83,7 @@ func NewSQLiteKeyBackupTable(db *sql.DB) (tables.KeyBackupTable, error) {
 		{&s.insertBackupKeyStmt, insertBackupKeySQL},
 		{&s.updateBackupKeyStmt, updateBackupKeySQL},
 		{&s.countKeysStmt, countKeysSQL},
-		{&s.selectKeysStmt, selectKeysSQL},
+		{&s.selectKeysStmt, selectBackupKeysSQL},
 		{&s.selectKeysByRoomIDStmt, selectKeysByRoomIDSQL},
 		{&s.selectKeysByRoomIDAndSessionIDStmt, selectKeysByRoomIDAndSessionIDSQL},
 	}.Prepare(db)
diff --git a/userapi/storage/sqlite3/key_changes_table.go b/userapi/storage/sqlite3/key_changes_table.go
new file mode 100644
index 00000000..923bb57e
--- /dev/null
+++ b/userapi/storage/sqlite3/key_changes_table.go
@@ -0,0 +1,125 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/storage/sqlite3/deltas"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+)
+
+var keyChangesSchema = `
+-- Stores key change information about users. Used to determine when to send updated device lists to clients.
+CREATE TABLE IF NOT EXISTS keyserver_key_changes (
+	change_id INTEGER PRIMARY KEY AUTOINCREMENT,
+	-- The key owner
+	user_id TEXT NOT NULL,
+	UNIQUE (user_id)
+);
+`
+
+// Replace based on user ID. We don't care how many times the user's keys have changed, only that they
+// have changed, hence we can just keep bumping the change ID for this user.
+const upsertKeyChangeSQL = "" +
+	"INSERT OR REPLACE INTO keyserver_key_changes (user_id)" +
+	" VALUES ($1)" +
+	" RETURNING change_id"
+
+const selectKeyChangesSQL = "" +
+	"SELECT user_id, change_id FROM keyserver_key_changes WHERE change_id > $1 AND change_id <= $2"
+
+type keyChangesStatements struct {
+	db                   *sql.DB
+	upsertKeyChangeStmt  *sql.Stmt
+	selectKeyChangesStmt *sql.Stmt
+}
+
+func NewSqliteKeyChangesTable(db *sql.DB) (tables.KeyChanges, error) {
+	s := &keyChangesStatements{
+		db: db,
+	}
+	_, err := db.Exec(keyChangesSchema)
+	if err != nil {
+		return s, err
+	}
+
+	if err = executeMigration(context.Background(), db); err != nil {
+		return nil, err
+	}
+
+	return s, sqlutil.StatementList{
+		{&s.upsertKeyChangeStmt, upsertKeyChangeSQL},
+		{&s.selectKeyChangesStmt, selectKeyChangesSQL},
+	}.Prepare(db)
+}
+
+func executeMigration(ctx context.Context, db *sql.DB) error {
+	// TODO: Remove when we are sure we are not having goose artefacts in the db
+	// This forces an error, which indicates the migration is already applied, since the
+	// column partition was removed from the table
+	migrationName := "keyserver: refactor key changes"
+
+	var cName string
+	err := db.QueryRowContext(ctx, `SELECT p.name FROM sqlite_master AS m JOIN pragma_table_info(m.name) AS p WHERE m.name = 'keyserver_key_changes' AND p.name = 'partition'`).Scan(&cName)
+	if err != nil {
+		if errors.Is(err, sql.ErrNoRows) { // migration was already executed, as the column was removed
+			if err = sqlutil.InsertMigration(ctx, db, migrationName); err != nil {
+				return fmt.Errorf("unable to manually insert migration '%s': %w", migrationName, err)
+			}
+			return nil
+		}
+		return err
+	}
+	m := sqlutil.NewMigrator(db)
+	m.AddMigrations(sqlutil.Migration{
+		Version: migrationName,
+		Up:      deltas.UpRefactorKeyChanges,
+	})
+	return m.Up(ctx)
+}
+
+func (s *keyChangesStatements) InsertKeyChange(ctx context.Context, userID string) (changeID int64, err error) {
+	err = s.upsertKeyChangeStmt.QueryRowContext(ctx, userID).Scan(&changeID)
+	return
+}
+
+func (s *keyChangesStatements) SelectKeyChanges(
+	ctx context.Context, fromOffset, toOffset int64,
+) (userIDs []string, latestOffset int64, err error) {
+	latestOffset = fromOffset
+	rows, err := s.selectKeyChangesStmt.QueryContext(ctx, fromOffset, toOffset)
+	if err != nil {
+		return nil, 0, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeyChangesStmt: rows.close() failed")
+	for rows.Next() {
+		var userID string
+		var offset int64
+		if err := rows.Scan(&userID, &offset); err != nil {
+			return nil, 0, err
+		}
+		if offset > latestOffset {
+			latestOffset = offset
+		}
+		userIDs = append(userIDs, userID)
+	}
+	return
+}
diff --git a/userapi/storage/sqlite3/one_time_keys_table.go b/userapi/storage/sqlite3/one_time_keys_table.go
new file mode 100644
index 00000000..a992d399
--- /dev/null
+++ b/userapi/storage/sqlite3/one_time_keys_table.go
@@ -0,0 +1,208 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+	"time"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+)
+
+var oneTimeKeysSchema = `
+-- Stores one-time public keys for users
+CREATE TABLE IF NOT EXISTS keyserver_one_time_keys (
+    user_id TEXT NOT NULL,
+	device_id TEXT NOT NULL,
+	key_id TEXT NOT NULL,
+	algorithm TEXT NOT NULL,
+	ts_added_secs BIGINT NOT NULL,
+	key_json TEXT NOT NULL,
+	-- Clobber based on 4-uple of user/device/key/algorithm.
+    UNIQUE (user_id, device_id, key_id, algorithm)
+);
+
+CREATE INDEX IF NOT EXISTS keyserver_one_time_keys_idx ON keyserver_one_time_keys (user_id, device_id);
+`
+
+const upsertKeysSQL = "" +
+	"INSERT INTO keyserver_one_time_keys (user_id, device_id, key_id, algorithm, ts_added_secs, key_json)" +
+	" VALUES ($1, $2, $3, $4, $5, $6)" +
+	" ON CONFLICT (user_id, device_id, key_id, algorithm)" +
+	" DO UPDATE SET key_json = $6"
+
+const selectOneTimeKeysSQL = "" +
+	"SELECT key_id, algorithm, key_json FROM keyserver_one_time_keys WHERE user_id=$1 AND device_id=$2"
+
+const selectKeysCountSQL = "" +
+	"SELECT algorithm, COUNT(key_id) FROM " +
+	" (SELECT algorithm, key_id FROM keyserver_one_time_keys WHERE user_id = $1 AND device_id = $2 LIMIT 100)" +
+	" x GROUP BY algorithm"
+
+const deleteOneTimeKeySQL = "" +
+	"DELETE FROM keyserver_one_time_keys WHERE user_id = $1 AND device_id = $2 AND algorithm = $3 AND key_id = $4"
+
+const selectKeyByAlgorithmSQL = "" +
+	"SELECT key_id, key_json FROM keyserver_one_time_keys WHERE user_id = $1 AND device_id = $2 AND algorithm = $3 LIMIT 1"
+
+const deleteOneTimeKeysSQL = "" +
+	"DELETE FROM keyserver_one_time_keys WHERE user_id = $1 AND device_id = $2"
+
+type oneTimeKeysStatements struct {
+	db                       *sql.DB
+	upsertKeysStmt           *sql.Stmt
+	selectKeysStmt           *sql.Stmt
+	selectKeysCountStmt      *sql.Stmt
+	selectKeyByAlgorithmStmt *sql.Stmt
+	deleteOneTimeKeyStmt     *sql.Stmt
+	deleteOneTimeKeysStmt    *sql.Stmt
+}
+
+func NewSqliteOneTimeKeysTable(db *sql.DB) (tables.OneTimeKeys, error) {
+	s := &oneTimeKeysStatements{
+		db: db,
+	}
+	_, err := db.Exec(oneTimeKeysSchema)
+	if err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.upsertKeysStmt, upsertKeysSQL},
+		{&s.selectKeysStmt, selectOneTimeKeysSQL},
+		{&s.selectKeysCountStmt, selectKeysCountSQL},
+		{&s.selectKeyByAlgorithmStmt, selectKeyByAlgorithmSQL},
+		{&s.deleteOneTimeKeyStmt, deleteOneTimeKeySQL},
+		{&s.deleteOneTimeKeysStmt, deleteOneTimeKeysSQL},
+	}.Prepare(db)
+}
+
+func (s *oneTimeKeysStatements) SelectOneTimeKeys(ctx context.Context, userID, deviceID string, keyIDsWithAlgorithms []string) (map[string]json.RawMessage, error) {
+	rows, err := s.selectKeysStmt.QueryContext(ctx, userID, deviceID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeysStmt: rows.close() failed")
+
+	wantSet := make(map[string]bool, len(keyIDsWithAlgorithms))
+	for _, ka := range keyIDsWithAlgorithms {
+		wantSet[ka] = true
+	}
+
+	result := make(map[string]json.RawMessage)
+	for rows.Next() {
+		var keyID string
+		var algorithm string
+		var keyJSONStr string
+		if err := rows.Scan(&keyID, &algorithm, &keyJSONStr); err != nil {
+			return nil, err
+		}
+		keyIDWithAlgo := algorithm + ":" + keyID
+		if wantSet[keyIDWithAlgo] {
+			result[keyIDWithAlgo] = json.RawMessage(keyJSONStr)
+		}
+	}
+	return result, rows.Err()
+}
+
+func (s *oneTimeKeysStatements) CountOneTimeKeys(ctx context.Context, userID, deviceID string) (*api.OneTimeKeysCount, error) {
+	counts := &api.OneTimeKeysCount{
+		DeviceID: deviceID,
+		UserID:   userID,
+		KeyCount: make(map[string]int),
+	}
+	rows, err := s.selectKeysCountStmt.QueryContext(ctx, userID, deviceID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeysCountStmt: rows.close() failed")
+	for rows.Next() {
+		var algorithm string
+		var count int
+		if err = rows.Scan(&algorithm, &count); err != nil {
+			return nil, err
+		}
+		counts.KeyCount[algorithm] = count
+	}
+	return counts, nil
+}
+
+func (s *oneTimeKeysStatements) InsertOneTimeKeys(
+	ctx context.Context, txn *sql.Tx, keys api.OneTimeKeys,
+) (*api.OneTimeKeysCount, error) {
+	now := time.Now().Unix()
+	counts := &api.OneTimeKeysCount{
+		DeviceID: keys.DeviceID,
+		UserID:   keys.UserID,
+		KeyCount: make(map[string]int),
+	}
+	for keyIDWithAlgo, keyJSON := range keys.KeyJSON {
+		algo, keyID := keys.Split(keyIDWithAlgo)
+		_, err := sqlutil.TxStmt(txn, s.upsertKeysStmt).ExecContext(
+			ctx, keys.UserID, keys.DeviceID, keyID, algo, now, string(keyJSON),
+		)
+		if err != nil {
+			return nil, err
+		}
+	}
+	rows, err := sqlutil.TxStmt(txn, s.selectKeysCountStmt).QueryContext(ctx, keys.UserID, keys.DeviceID)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeysCountStmt: rows.close() failed")
+	for rows.Next() {
+		var algorithm string
+		var count int
+		if err = rows.Scan(&algorithm, &count); err != nil {
+			return nil, err
+		}
+		counts.KeyCount[algorithm] = count
+	}
+
+	return counts, rows.Err()
+}
+
+func (s *oneTimeKeysStatements) SelectAndDeleteOneTimeKey(
+	ctx context.Context, txn *sql.Tx, userID, deviceID, algorithm string,
+) (map[string]json.RawMessage, error) {
+	var keyID string
+	var keyJSON string
+	err := sqlutil.TxStmtContext(ctx, txn, s.selectKeyByAlgorithmStmt).QueryRowContext(ctx, userID, deviceID, algorithm).Scan(&keyID, &keyJSON)
+	if err != nil {
+		if err == sql.ErrNoRows {
+			return nil, nil
+		}
+		return nil, err
+	}
+	_, err = sqlutil.TxStmtContext(ctx, txn, s.deleteOneTimeKeyStmt).ExecContext(ctx, userID, deviceID, algorithm, keyID)
+	if err != nil {
+		return nil, err
+	}
+	if keyJSON == "" {
+		return nil, nil
+	}
+	return map[string]json.RawMessage{
+		algorithm + ":" + keyID: json.RawMessage(keyJSON),
+	}, err
+}
+
+func (s *oneTimeKeysStatements) DeleteOneTimeKeys(ctx context.Context, txn *sql.Tx, userID, deviceID string) error {
+	_, err := sqlutil.TxStmt(txn, s.deleteOneTimeKeysStmt).ExecContext(ctx, userID, deviceID)
+	return err
+}
diff --git a/userapi/storage/sqlite3/stale_device_lists.go b/userapi/storage/sqlite3/stale_device_lists.go
new file mode 100644
index 00000000..f078fc99
--- /dev/null
+++ b/userapi/storage/sqlite3/stale_device_lists.go
@@ -0,0 +1,145 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"strings"
+	"time"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+var staleDeviceListsSchema = `
+-- Stores whether a user's device lists are stale or not.
+CREATE TABLE IF NOT EXISTS keyserver_stale_device_lists (
+    user_id TEXT PRIMARY KEY NOT NULL,
+	domain TEXT NOT NULL,
+	is_stale BOOLEAN NOT NULL,
+	ts_added_secs BIGINT NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS keyserver_stale_device_lists_idx ON keyserver_stale_device_lists (domain, is_stale);
+`
+
+const upsertStaleDeviceListSQL = "" +
+	"INSERT INTO keyserver_stale_device_lists (user_id, domain, is_stale, ts_added_secs)" +
+	" VALUES ($1, $2, $3, $4)" +
+	" ON CONFLICT (user_id)" +
+	" DO UPDATE SET is_stale = $3, ts_added_secs = $4"
+
+const selectStaleDeviceListsWithDomainsSQL = "" +
+	"SELECT user_id FROM keyserver_stale_device_lists WHERE is_stale = $1 AND domain = $2 ORDER BY ts_added_secs DESC"
+
+const selectStaleDeviceListsSQL = "" +
+	"SELECT user_id FROM keyserver_stale_device_lists WHERE is_stale = $1 ORDER BY ts_added_secs DESC"
+
+const deleteStaleDevicesSQL = "" +
+	"DELETE FROM keyserver_stale_device_lists WHERE user_id IN ($1)"
+
+type staleDeviceListsStatements struct {
+	db                                    *sql.DB
+	upsertStaleDeviceListStmt             *sql.Stmt
+	selectStaleDeviceListsWithDomainsStmt *sql.Stmt
+	selectStaleDeviceListsStmt            *sql.Stmt
+	// deleteStaleDeviceListsStmt            *sql.Stmt // Prepared at runtime
+}
+
+func NewSqliteStaleDeviceListsTable(db *sql.DB) (tables.StaleDeviceLists, error) {
+	s := &staleDeviceListsStatements{
+		db: db,
+	}
+	_, err := db.Exec(staleDeviceListsSchema)
+	if err != nil {
+		return nil, err
+	}
+	return s, sqlutil.StatementList{
+		{&s.upsertStaleDeviceListStmt, upsertStaleDeviceListSQL},
+		{&s.selectStaleDeviceListsStmt, selectStaleDeviceListsSQL},
+		{&s.selectStaleDeviceListsWithDomainsStmt, selectStaleDeviceListsWithDomainsSQL},
+		// { &s.deleteStaleDeviceListsStmt, deleteStaleDevicesSQL}, // Prepared at runtime
+	}.Prepare(db)
+}
+
+func (s *staleDeviceListsStatements) InsertStaleDeviceList(ctx context.Context, userID string, isStale bool) error {
+	_, domain, err := gomatrixserverlib.SplitID('@', userID)
+	if err != nil {
+		return err
+	}
+	_, err = s.upsertStaleDeviceListStmt.ExecContext(ctx, userID, string(domain), isStale, gomatrixserverlib.AsTimestamp(time.Now()))
+	return err
+}
+
+func (s *staleDeviceListsStatements) SelectUserIDsWithStaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error) {
+	// we only query for 1 domain or all domains so optimise for those use cases
+	if len(domains) == 0 {
+		rows, err := s.selectStaleDeviceListsStmt.QueryContext(ctx, true)
+		if err != nil {
+			return nil, err
+		}
+		return rowsToUserIDs(ctx, rows)
+	}
+	var result []string
+	for _, domain := range domains {
+		rows, err := s.selectStaleDeviceListsWithDomainsStmt.QueryContext(ctx, true, string(domain))
+		if err != nil {
+			return nil, err
+		}
+		userIDs, err := rowsToUserIDs(ctx, rows)
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, userIDs...)
+	}
+	return result, nil
+}
+
+// DeleteStaleDeviceLists removes users from stale device lists
+func (s *staleDeviceListsStatements) DeleteStaleDeviceLists(
+	ctx context.Context, txn *sql.Tx, userIDs []string,
+) error {
+	qry := strings.Replace(deleteStaleDevicesSQL, "($1)", sqlutil.QueryVariadic(len(userIDs)), 1)
+	stmt, err := s.db.Prepare(qry)
+	if err != nil {
+		return err
+	}
+	defer internal.CloseAndLogIfError(ctx, stmt, "DeleteStaleDeviceLists: stmt.Close failed")
+	stmt = sqlutil.TxStmt(txn, stmt)
+
+	params := make([]any, len(userIDs))
+	for i := range userIDs {
+		params[i] = userIDs[i]
+	}
+
+	_, err = stmt.ExecContext(ctx, params...)
+	return err
+}
+
+func rowsToUserIDs(ctx context.Context, rows *sql.Rows) (result []string, err error) {
+	defer internal.CloseAndLogIfError(ctx, rows, "closing rowsToUserIDs failed")
+	for rows.Next() {
+		var userID string
+		if err := rows.Scan(&userID); err != nil {
+			return nil, err
+		}
+		result = append(result, userID)
+	}
+	return result, rows.Err()
+}
diff --git a/userapi/storage/sqlite3/stats_table.go b/userapi/storage/sqlite3/stats_table.go
index a1365c94..72b3ba49 100644
--- a/userapi/storage/sqlite3/stats_table.go
+++ b/userapi/storage/sqlite3/stats_table.go
@@ -256,6 +256,7 @@ func (s *statsStatements) allUsers(ctx context.Context, txn *sql.Tx) (result int
 	if err != nil {
 		return 0, err
 	}
+	defer internal.CloseAndLogIfError(ctx, queryStmt, "allUsers.StmtClose() failed")
 	stmt := sqlutil.TxStmt(txn, queryStmt)
 	err = stmt.QueryRowContext(ctx,
 		1, 2, 3, 4,
@@ -269,6 +270,7 @@ func (s *statsStatements) nonBridgedUsers(ctx context.Context, txn *sql.Tx) (res
 	if err != nil {
 		return 0, err
 	}
+	defer internal.CloseAndLogIfError(ctx, queryStmt, "nonBridgedUsers.StmtClose() failed")
 	stmt := sqlutil.TxStmt(txn, queryStmt)
 	err = stmt.QueryRowContext(ctx,
 		1, 2, 3,
@@ -286,6 +288,7 @@ func (s *statsStatements) registeredUserByType(ctx context.Context, txn *sql.Tx)
 	if err != nil {
 		return nil, err
 	}
+	defer internal.CloseAndLogIfError(ctx, queryStmt, "registeredUserByType.StmtClose() failed")
 	stmt := sqlutil.TxStmt(txn, queryStmt)
 	registeredAfter := time.Now().AddDate(0, 0, -30)
 
diff --git a/userapi/storage/sqlite3/storage.go b/userapi/storage/sqlite3/storage.go
index 85a1f706..0f3eeed1 100644
--- a/userapi/storage/sqlite3/storage.go
+++ b/userapi/storage/sqlite3/storage.go
@@ -30,8 +30,8 @@ import (
 	"github.com/matrix-org/dendrite/userapi/storage/sqlite3/deltas"
 )
 
-// NewDatabase creates a new accounts and profiles database
-func NewDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions, serverName gomatrixserverlib.ServerName, bcryptCost int, openIDTokenLifetimeMS int64, loginTokenLifetime time.Duration, serverNoticesLocalpart string) (*shared.Database, error) {
+// NewUserDatabase creates a new accounts and profiles database
+func NewUserDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions, serverName gomatrixserverlib.ServerName, bcryptCost int, openIDTokenLifetimeMS int64, loginTokenLifetime time.Duration, serverNoticesLocalpart string) (*shared.Database, error) {
 	db, writer, err := base.DatabaseConnection(dbProperties, sqlutil.NewExclusiveWriter())
 	if err != nil {
 		return nil, err
@@ -134,3 +134,44 @@ func NewDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions,
 		OpenIDTokenLifetimeMS: openIDTokenLifetimeMS,
 	}, nil
 }
+
+func NewKeyDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions) (*shared.KeyDatabase, error) {
+	db, writer, err := base.DatabaseConnection(dbProperties, sqlutil.NewExclusiveWriter())
+	if err != nil {
+		return nil, err
+	}
+	otk, err := NewSqliteOneTimeKeysTable(db)
+	if err != nil {
+		return nil, err
+	}
+	dk, err := NewSqliteDeviceKeysTable(db)
+	if err != nil {
+		return nil, err
+	}
+	kc, err := NewSqliteKeyChangesTable(db)
+	if err != nil {
+		return nil, err
+	}
+	sdl, err := NewSqliteStaleDeviceListsTable(db)
+	if err != nil {
+		return nil, err
+	}
+	csk, err := NewSqliteCrossSigningKeysTable(db)
+	if err != nil {
+		return nil, err
+	}
+	css, err := NewSqliteCrossSigningSigsTable(db)
+	if err != nil {
+		return nil, err
+	}
+
+	return &shared.KeyDatabase{
+		OneTimeKeysTable:      otk,
+		DeviceKeysTable:       dk,
+		KeyChangesTable:       kc,
+		StaleDeviceListsTable: sdl,
+		CrossSigningKeysTable: csk,
+		CrossSigningSigsTable: css,
+		Writer:                writer,
+	}, nil
+}
diff --git a/userapi/storage/storage.go b/userapi/storage/storage.go
index 42221e75..0329fb46 100644
--- a/userapi/storage/storage.go
+++ b/userapi/storage/storage.go
@@ -29,15 +29,36 @@ import (
 	"github.com/matrix-org/dendrite/userapi/storage/sqlite3"
 )
 
-// NewUserAPIDatabase opens a new Postgres or Sqlite database (based on dataSourceName scheme)
+// NewUserDatabase opens a new Postgres or Sqlite database (based on dataSourceName scheme)
 // and sets postgres connection parameters
-func NewUserAPIDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions, serverName gomatrixserverlib.ServerName, bcryptCost int, openIDTokenLifetimeMS int64, loginTokenLifetime time.Duration, serverNoticesLocalpart string) (Database, error) {
+func NewUserDatabase(
+	base *base.BaseDendrite,
+	dbProperties *config.DatabaseOptions,
+	serverName gomatrixserverlib.ServerName,
+	bcryptCost int,
+	openIDTokenLifetimeMS int64,
+	loginTokenLifetime time.Duration,
+	serverNoticesLocalpart string,
+) (UserDatabase, error) {
 	switch {
 	case dbProperties.ConnectionString.IsSQLite():
-		return sqlite3.NewDatabase(base, dbProperties, serverName, bcryptCost, openIDTokenLifetimeMS, loginTokenLifetime, serverNoticesLocalpart)
+		return sqlite3.NewUserDatabase(base, dbProperties, serverName, bcryptCost, openIDTokenLifetimeMS, loginTokenLifetime, serverNoticesLocalpart)
 	case dbProperties.ConnectionString.IsPostgres():
 		return postgres.NewDatabase(base, dbProperties, serverName, bcryptCost, openIDTokenLifetimeMS, loginTokenLifetime, serverNoticesLocalpart)
 	default:
 		return nil, fmt.Errorf("unexpected database type")
 	}
 }
+
+// NewKeyDatabase opens a new Postgres or Sqlite database (base on dataSourceName) scheme)
+// and sets postgres connection parameters.
+func NewKeyDatabase(base *base.BaseDendrite, dbProperties *config.DatabaseOptions) (KeyDatabase, error) {
+	switch {
+	case dbProperties.ConnectionString.IsSQLite():
+		return sqlite3.NewKeyDatabase(base, dbProperties)
+	case dbProperties.ConnectionString.IsPostgres():
+		return postgres.NewKeyDatabase(base, dbProperties)
+	default:
+		return nil, fmt.Errorf("unexpected database type")
+	}
+}
diff --git a/userapi/storage/storage_test.go b/userapi/storage/storage_test.go
index 23aafff0..f52e7e17 100644
--- a/userapi/storage/storage_test.go
+++ b/userapi/storage/storage_test.go
@@ -4,9 +4,12 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"reflect"
+	"sync"
 	"testing"
 	"time"
 
+	"github.com/matrix-org/dendrite/userapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/matrix-org/util"
 	"github.com/stretchr/testify/assert"
@@ -29,14 +32,14 @@ var (
 	ctx              = context.Background()
 )
 
-func mustCreateDatabase(t *testing.T, dbType test.DBType) (storage.Database, func()) {
+func mustCreateUserDatabase(t *testing.T, dbType test.DBType) (storage.UserDatabase, func()) {
 	base, baseclose := testrig.CreateBaseDendrite(t, dbType)
 	connStr, close := test.PrepareDBConnectionString(t, dbType)
-	db, err := storage.NewUserAPIDatabase(base, &config.DatabaseOptions{
+	db, err := storage.NewUserDatabase(base, &config.DatabaseOptions{
 		ConnectionString: config.DataSource(connStr),
 	}, "localhost", bcrypt.MinCost, openIDLifetimeMS, loginTokenLifetime, "_server")
 	if err != nil {
-		t.Fatalf("NewUserAPIDatabase returned %s", err)
+		t.Fatalf("NewUserDatabase returned %s", err)
 	}
 	return db, func() {
 		close()
@@ -47,7 +50,7 @@ func mustCreateDatabase(t *testing.T, dbType test.DBType) (storage.Database, fun
 // Tests storing and getting account data
 func Test_AccountData(t *testing.T) {
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 		alice := test.NewUser(t)
 		localpart, domain, err := gomatrixserverlib.SplitID('@', alice.ID)
@@ -78,7 +81,7 @@ func Test_AccountData(t *testing.T) {
 // Tests the creation of accounts
 func Test_Accounts(t *testing.T) {
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 		alice := test.NewUser(t)
 		aliceLocalpart, aliceDomain, err := gomatrixserverlib.SplitID('@', alice.ID)
@@ -158,7 +161,7 @@ func Test_Devices(t *testing.T) {
 	accessToken := util.RandomString(16)
 
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 
 		deviceWithID, err := db.CreateDevice(ctx, localpart, domain, &deviceID, accessToken, nil, "", "")
@@ -238,7 +241,7 @@ func Test_KeyBackup(t *testing.T) {
 	room := test.NewRoom(t, alice)
 
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 
 		wantAuthData := json.RawMessage("my auth data")
@@ -315,7 +318,7 @@ func Test_KeyBackup(t *testing.T) {
 func Test_LoginToken(t *testing.T) {
 	alice := test.NewUser(t)
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 
 		// create a new token
@@ -347,7 +350,7 @@ func Test_OpenID(t *testing.T) {
 	token := util.RandomString(24)
 
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 
 		expiresAtMS := time.Now().UnixNano()/int64(time.Millisecond) + openIDLifetimeMS
@@ -368,7 +371,7 @@ func Test_Profile(t *testing.T) {
 	assert.NoError(t, err)
 
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 
 		// create account, which also creates a profile
@@ -417,7 +420,7 @@ func Test_Pusher(t *testing.T) {
 	assert.NoError(t, err)
 
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 
 		appID := util.RandomString(8)
@@ -468,7 +471,7 @@ func Test_ThreePID(t *testing.T) {
 	assert.NoError(t, err)
 
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 		threePID := util.RandomString(8)
 		medium := util.RandomString(8)
@@ -507,7 +510,7 @@ func Test_Notification(t *testing.T) {
 	room := test.NewRoom(t, alice)
 	room2 := test.NewRoom(t, alice)
 	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
-		db, close := mustCreateDatabase(t, dbType)
+		db, close := mustCreateUserDatabase(t, dbType)
 		defer close()
 		// generate some dummy notifications
 		for i := 0; i < 10; i++ {
@@ -571,3 +574,184 @@ func Test_Notification(t *testing.T) {
 		assert.Equal(t, int64(0), total)
 	})
 }
+
+func mustCreateKeyDatabase(t *testing.T, dbType test.DBType) (storage.KeyDatabase, func()) {
+	base, close := testrig.CreateBaseDendrite(t, dbType)
+	db, err := storage.NewKeyDatabase(base, &base.Cfg.KeyServer.Database)
+	if err != nil {
+		t.Fatalf("failed to create new database: %v", err)
+	}
+	return db, close
+}
+
+func MustNotError(t *testing.T, err error) {
+	t.Helper()
+	if err == nil {
+		return
+	}
+	t.Fatalf("operation failed: %s", err)
+}
+
+func TestKeyChanges(t *testing.T) {
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		db, clean := mustCreateKeyDatabase(t, dbType)
+		defer clean()
+		_, err := db.StoreKeyChange(ctx, "@alice:localhost")
+		MustNotError(t, err)
+		deviceChangeIDB, err := db.StoreKeyChange(ctx, "@bob:localhost")
+		MustNotError(t, err)
+		deviceChangeIDC, err := db.StoreKeyChange(ctx, "@charlie:localhost")
+		MustNotError(t, err)
+		userIDs, latest, err := db.KeyChanges(ctx, deviceChangeIDB, types.OffsetNewest)
+		if err != nil {
+			t.Fatalf("Failed to KeyChanges: %s", err)
+		}
+		if latest != deviceChangeIDC {
+			t.Fatalf("KeyChanges: got latest=%d want %d", latest, deviceChangeIDC)
+		}
+		if !reflect.DeepEqual(userIDs, []string{"@charlie:localhost"}) {
+			t.Fatalf("KeyChanges: wrong user_ids: %v", userIDs)
+		}
+	})
+}
+
+func TestKeyChangesNoDupes(t *testing.T) {
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		db, clean := mustCreateKeyDatabase(t, dbType)
+		defer clean()
+		deviceChangeIDA, err := db.StoreKeyChange(ctx, "@alice:localhost")
+		MustNotError(t, err)
+		deviceChangeIDB, err := db.StoreKeyChange(ctx, "@alice:localhost")
+		MustNotError(t, err)
+		if deviceChangeIDA == deviceChangeIDB {
+			t.Fatalf("Expected change ID to be different even when inserting key change for the same user, got %d for both changes", deviceChangeIDA)
+		}
+		deviceChangeID, err := db.StoreKeyChange(ctx, "@alice:localhost")
+		MustNotError(t, err)
+		userIDs, latest, err := db.KeyChanges(ctx, 0, types.OffsetNewest)
+		if err != nil {
+			t.Fatalf("Failed to KeyChanges: %s", err)
+		}
+		if latest != deviceChangeID {
+			t.Fatalf("KeyChanges: got latest=%d want %d", latest, deviceChangeID)
+		}
+		if !reflect.DeepEqual(userIDs, []string{"@alice:localhost"}) {
+			t.Fatalf("KeyChanges: wrong user_ids: %v", userIDs)
+		}
+	})
+}
+
+func TestKeyChangesUpperLimit(t *testing.T) {
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		db, clean := mustCreateKeyDatabase(t, dbType)
+		defer clean()
+		deviceChangeIDA, err := db.StoreKeyChange(ctx, "@alice:localhost")
+		MustNotError(t, err)
+		deviceChangeIDB, err := db.StoreKeyChange(ctx, "@bob:localhost")
+		MustNotError(t, err)
+		_, err = db.StoreKeyChange(ctx, "@charlie:localhost")
+		MustNotError(t, err)
+		userIDs, latest, err := db.KeyChanges(ctx, deviceChangeIDA, deviceChangeIDB)
+		if err != nil {
+			t.Fatalf("Failed to KeyChanges: %s", err)
+		}
+		if latest != deviceChangeIDB {
+			t.Fatalf("KeyChanges: got latest=%d want %d", latest, deviceChangeIDB)
+		}
+		if !reflect.DeepEqual(userIDs, []string{"@bob:localhost"}) {
+			t.Fatalf("KeyChanges: wrong user_ids: %v", userIDs)
+		}
+	})
+}
+
+var dbLock sync.Mutex
+var deviceArray = []string{"AAA", "another_device"}
+
+// The purpose of this test is to make sure that the storage layer is generating sequential stream IDs per user,
+// and that they are returned correctly when querying for device keys.
+func TestDeviceKeysStreamIDGeneration(t *testing.T) {
+	var err error
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		db, clean := mustCreateKeyDatabase(t, dbType)
+		defer clean()
+		alice := "@alice:TestDeviceKeysStreamIDGeneration"
+		bob := "@bob:TestDeviceKeysStreamIDGeneration"
+		msgs := []api.DeviceMessage{
+			{
+				Type: api.TypeDeviceKeyUpdate,
+				DeviceKeys: &api.DeviceKeys{
+					DeviceID: "AAA",
+					UserID:   alice,
+					KeyJSON:  []byte(`{"key":"v1"}`),
+				},
+				// StreamID: 1
+			},
+			{
+				Type: api.TypeDeviceKeyUpdate,
+				DeviceKeys: &api.DeviceKeys{
+					DeviceID: "AAA",
+					UserID:   bob,
+					KeyJSON:  []byte(`{"key":"v1"}`),
+				},
+				// StreamID: 1 as this is a different user
+			},
+			{
+				Type: api.TypeDeviceKeyUpdate,
+				DeviceKeys: &api.DeviceKeys{
+					DeviceID: "another_device",
+					UserID:   alice,
+					KeyJSON:  []byte(`{"key":"v1"}`),
+				},
+				// StreamID: 2 as this is a 2nd device key
+			},
+		}
+		MustNotError(t, db.StoreLocalDeviceKeys(ctx, msgs))
+		if msgs[0].StreamID != 1 {
+			t.Fatalf("Expected StoreLocalDeviceKeys to set StreamID=1 but got %d", msgs[0].StreamID)
+		}
+		if msgs[1].StreamID != 1 {
+			t.Fatalf("Expected StoreLocalDeviceKeys to set StreamID=1 (different user) but got %d", msgs[1].StreamID)
+		}
+		if msgs[2].StreamID != 2 {
+			t.Fatalf("Expected StoreLocalDeviceKeys to set StreamID=2 (another device) but got %d", msgs[2].StreamID)
+		}
+
+		// updating a device sets the next stream ID for that user
+		msgs = []api.DeviceMessage{
+			{
+				Type: api.TypeDeviceKeyUpdate,
+				DeviceKeys: &api.DeviceKeys{
+					DeviceID: "AAA",
+					UserID:   alice,
+					KeyJSON:  []byte(`{"key":"v2"}`),
+				},
+				// StreamID: 3
+			},
+		}
+		MustNotError(t, db.StoreLocalDeviceKeys(ctx, msgs))
+		if msgs[0].StreamID != 3 {
+			t.Fatalf("Expected StoreLocalDeviceKeys to set StreamID=3 (new key same device) but got %d", msgs[0].StreamID)
+		}
+
+		dbLock.Lock()
+		defer dbLock.Unlock()
+		// Querying for device keys returns the latest stream IDs
+		msgs, err = db.DeviceKeysForUser(ctx, alice, deviceArray, false)
+
+		if err != nil {
+			t.Fatalf("DeviceKeysForUser returned error: %s", err)
+		}
+		wantStreamIDs := map[string]int64{
+			"AAA":            3,
+			"another_device": 2,
+		}
+		if len(msgs) != len(wantStreamIDs) {
+			t.Fatalf("DeviceKeysForUser: wrong number of devices, got %d want %d", len(msgs), len(wantStreamIDs))
+		}
+		for _, m := range msgs {
+			if m.StreamID != wantStreamIDs[m.DeviceID] {
+				t.Errorf("DeviceKeysForUser: wrong returned stream ID for key, got %d want %d", m.StreamID, wantStreamIDs[m.DeviceID])
+			}
+		}
+	})
+}
diff --git a/userapi/storage/storage_wasm.go b/userapi/storage/storage_wasm.go
index 5d5d292e..163e3e17 100644
--- a/userapi/storage/storage_wasm.go
+++ b/userapi/storage/storage_wasm.go
@@ -32,10 +32,10 @@ func NewUserAPIDatabase(
 	openIDTokenLifetimeMS int64,
 	loginTokenLifetime time.Duration,
 	serverNoticesLocalpart string,
-) (Database, error) {
+) (UserDatabase, error) {
 	switch {
 	case dbProperties.ConnectionString.IsSQLite():
-		return sqlite3.NewDatabase(base, dbProperties, serverName, bcryptCost, openIDTokenLifetimeMS, loginTokenLifetime, serverNoticesLocalpart)
+		return sqlite3.NewUserDatabase(base, dbProperties, serverName, bcryptCost, openIDTokenLifetimeMS, loginTokenLifetime, serverNoticesLocalpart)
 	case dbProperties.ConnectionString.IsPostgres():
 		return nil, fmt.Errorf("can't use Postgres implementation")
 	default:
diff --git a/userapi/storage/tables/interface.go b/userapi/storage/tables/interface.go
index 9221e571..693e7303 100644
--- a/userapi/storage/tables/interface.go
+++ b/userapi/storage/tables/interface.go
@@ -20,10 +20,10 @@ import (
 	"encoding/json"
 	"time"
 
+	"github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
 
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
-	"github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/dendrite/userapi/types"
 )
 
@@ -145,3 +145,47 @@ const (
 	// uint32.
 	AllNotifications NotificationFilter = (1 << 31) - 1
 )
+
+type OneTimeKeys interface {
+	SelectOneTimeKeys(ctx context.Context, userID, deviceID string, keyIDsWithAlgorithms []string) (map[string]json.RawMessage, error)
+	CountOneTimeKeys(ctx context.Context, userID, deviceID string) (*api.OneTimeKeysCount, error)
+	InsertOneTimeKeys(ctx context.Context, txn *sql.Tx, keys api.OneTimeKeys) (*api.OneTimeKeysCount, error)
+	// SelectAndDeleteOneTimeKey selects a single one time key matching the user/device/algorithm specified and returns the algo:key_id => JSON.
+	// Returns an empty map if the key does not exist.
+	SelectAndDeleteOneTimeKey(ctx context.Context, txn *sql.Tx, userID, deviceID, algorithm string) (map[string]json.RawMessage, error)
+	DeleteOneTimeKeys(ctx context.Context, txn *sql.Tx, userID, deviceID string) error
+}
+
+type DeviceKeys interface {
+	SelectDeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error
+	InsertDeviceKeys(ctx context.Context, txn *sql.Tx, keys []api.DeviceMessage) error
+	SelectMaxStreamIDForUser(ctx context.Context, txn *sql.Tx, userID string) (streamID int64, err error)
+	CountStreamIDsForUser(ctx context.Context, userID string, streamIDs []int64) (int, error)
+	SelectBatchDeviceKeys(ctx context.Context, userID string, deviceIDs []string, includeEmpty bool) ([]api.DeviceMessage, error)
+	DeleteDeviceKeys(ctx context.Context, txn *sql.Tx, userID, deviceID string) error
+	DeleteAllDeviceKeys(ctx context.Context, txn *sql.Tx, userID string) error
+}
+
+type KeyChanges interface {
+	InsertKeyChange(ctx context.Context, userID string) (int64, error)
+	// SelectKeyChanges returns the set (de-duplicated) of users who have changed their keys between the two offsets.
+	// Results are exclusive of fromOffset and inclusive of toOffset. A toOffset of types.OffsetNewest means no upper offset.
+	SelectKeyChanges(ctx context.Context, fromOffset, toOffset int64) (userIDs []string, latestOffset int64, err error)
+}
+
+type StaleDeviceLists interface {
+	InsertStaleDeviceList(ctx context.Context, userID string, isStale bool) error
+	SelectUserIDsWithStaleDeviceLists(ctx context.Context, domains []gomatrixserverlib.ServerName) ([]string, error)
+	DeleteStaleDeviceLists(ctx context.Context, txn *sql.Tx, userIDs []string) error
+}
+
+type CrossSigningKeys interface {
+	SelectCrossSigningKeysForUser(ctx context.Context, txn *sql.Tx, userID string) (r types.CrossSigningKeyMap, err error)
+	UpsertCrossSigningKeysForUser(ctx context.Context, txn *sql.Tx, userID string, keyType gomatrixserverlib.CrossSigningKeyPurpose, keyData gomatrixserverlib.Base64Bytes) error
+}
+
+type CrossSigningSigs interface {
+	SelectCrossSigningSigsForTarget(ctx context.Context, txn *sql.Tx, originUserID, targetUserID string, targetKeyID gomatrixserverlib.KeyID) (r types.CrossSigningSigMap, err error)
+	UpsertCrossSigningSigsForTarget(ctx context.Context, txn *sql.Tx, originUserID string, originKeyID gomatrixserverlib.KeyID, targetUserID string, targetKeyID gomatrixserverlib.KeyID, signature gomatrixserverlib.Base64Bytes) error
+	DeleteCrossSigningSigsForTarget(ctx context.Context, txn *sql.Tx, targetUserID string, targetKeyID gomatrixserverlib.KeyID) error
+}
diff --git a/userapi/storage/tables/stale_device_lists_test.go b/userapi/storage/tables/stale_device_lists_test.go
new file mode 100644
index 00000000..b9bdafda
--- /dev/null
+++ b/userapi/storage/tables/stale_device_lists_test.go
@@ -0,0 +1,94 @@
+package tables_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/matrix-org/dendrite/userapi/storage/postgres"
+	"github.com/matrix-org/dendrite/userapi/storage/sqlite3"
+	"github.com/matrix-org/gomatrixserverlib"
+
+	"github.com/matrix-org/dendrite/internal/sqlutil"
+	"github.com/matrix-org/dendrite/setup/config"
+
+	"github.com/matrix-org/dendrite/test"
+	"github.com/matrix-org/dendrite/userapi/storage/tables"
+)
+
+func mustCreateTable(t *testing.T, dbType test.DBType) (tab tables.StaleDeviceLists, close func()) {
+	connStr, close := test.PrepareDBConnectionString(t, dbType)
+	db, err := sqlutil.Open(&config.DatabaseOptions{
+		ConnectionString: config.DataSource(connStr),
+	}, nil)
+	if err != nil {
+		t.Fatalf("failed to open database: %s", err)
+	}
+	switch dbType {
+	case test.DBTypePostgres:
+		tab, err = postgres.NewPostgresStaleDeviceListsTable(db)
+	case test.DBTypeSQLite:
+		tab, err = sqlite3.NewSqliteStaleDeviceListsTable(db)
+	}
+	if err != nil {
+		t.Fatalf("failed to create new table: %s", err)
+	}
+	return tab, close
+}
+
+func TestStaleDeviceLists(t *testing.T) {
+	alice := test.NewUser(t)
+	bob := test.NewUser(t)
+	charlie := "@charlie:localhost"
+	ctx := context.Background()
+
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		tab, closeDB := mustCreateTable(t, dbType)
+		defer closeDB()
+
+		if err := tab.InsertStaleDeviceList(ctx, alice.ID, true); err != nil {
+			t.Fatalf("failed to insert stale device: %s", err)
+		}
+		if err := tab.InsertStaleDeviceList(ctx, bob.ID, true); err != nil {
+			t.Fatalf("failed to insert stale device: %s", err)
+		}
+		if err := tab.InsertStaleDeviceList(ctx, charlie, true); err != nil {
+			t.Fatalf("failed to insert stale device: %s", err)
+		}
+
+		// Query one server
+		wantStaleUsers := []string{alice.ID, bob.ID}
+		gotStaleUsers, err := tab.SelectUserIDsWithStaleDeviceLists(ctx, []gomatrixserverlib.ServerName{"test"})
+		if err != nil {
+			t.Fatalf("failed to query stale device lists: %s", err)
+		}
+		if !test.UnsortedStringSliceEqual(wantStaleUsers, gotStaleUsers) {
+			t.Fatalf("expected stale users %v, got %v", wantStaleUsers, gotStaleUsers)
+		}
+
+		// Query all servers
+		wantStaleUsers = []string{alice.ID, bob.ID, charlie}
+		gotStaleUsers, err = tab.SelectUserIDsWithStaleDeviceLists(ctx, []gomatrixserverlib.ServerName{})
+		if err != nil {
+			t.Fatalf("failed to query stale device lists: %s", err)
+		}
+		if !test.UnsortedStringSliceEqual(wantStaleUsers, gotStaleUsers) {
+			t.Fatalf("expected stale users %v, got %v", wantStaleUsers, gotStaleUsers)
+		}
+
+		// Delete stale devices
+		deleteUsers := []string{alice.ID, bob.ID}
+		if err = tab.DeleteStaleDeviceLists(ctx, nil, deleteUsers); err != nil {
+			t.Fatalf("failed to delete stale device lists: %s", err)
+		}
+
+		// Verify we don't get anything back after deleting
+		gotStaleUsers, err = tab.SelectUserIDsWithStaleDeviceLists(ctx, []gomatrixserverlib.ServerName{"test"})
+		if err != nil {
+			t.Fatalf("failed to query stale device lists: %s", err)
+		}
+
+		if gotCount := len(gotStaleUsers); gotCount > 0 {
+			t.Fatalf("expected no stale users, got %d", gotCount)
+		}
+	})
+}
diff --git a/userapi/types/storage.go b/userapi/types/storage.go
new file mode 100644
index 00000000..7fb90454
--- /dev/null
+++ b/userapi/types/storage.go
@@ -0,0 +1,50 @@
+// Copyright 2021 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package types
+
+import (
+	"math"
+
+	"github.com/matrix-org/gomatrixserverlib"
+)
+
+const (
+	// OffsetNewest tells e.g. the database to get the most current data
+	OffsetNewest int64 = math.MaxInt64
+	// OffsetOldest tells e.g. the database to get the oldest data
+	OffsetOldest int64 = 0
+)
+
+// KeyTypePurposeToInt maps a purpose to an integer, which is used in the
+// database to reduce the amount of space taken up by this column.
+var KeyTypePurposeToInt = map[gomatrixserverlib.CrossSigningKeyPurpose]int16{
+	gomatrixserverlib.CrossSigningKeyPurposeMaster:      1,
+	gomatrixserverlib.CrossSigningKeyPurposeSelfSigning: 2,
+	gomatrixserverlib.CrossSigningKeyPurposeUserSigning: 3,
+}
+
+// KeyTypeIntToPurpose maps an integer to a purpose, which is used in the
+// database to reduce the amount of space taken up by this column.
+var KeyTypeIntToPurpose = map[int16]gomatrixserverlib.CrossSigningKeyPurpose{
+	1: gomatrixserverlib.CrossSigningKeyPurposeMaster,
+	2: gomatrixserverlib.CrossSigningKeyPurposeSelfSigning,
+	3: gomatrixserverlib.CrossSigningKeyPurposeUserSigning,
+}
+
+// Map of purpose -> public key
+type CrossSigningKeyMap map[gomatrixserverlib.CrossSigningKeyPurpose]gomatrixserverlib.Base64Bytes
+
+// Map of user ID -> key ID -> signature
+type CrossSigningSigMap map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes
diff --git a/userapi/userapi.go b/userapi/userapi.go
index 2dd81d75..826bd721 100644
--- a/userapi/userapi.go
+++ b/userapi/userapi.go
@@ -17,13 +17,11 @@ package userapi
 import (
 	"time"
 
+	fedsenderapi "github.com/matrix-org/dendrite/federationapi/api"
 	"github.com/sirupsen/logrus"
 
-	"github.com/matrix-org/dendrite/internal/pushgateway"
-	keyapi "github.com/matrix-org/dendrite/keyserver/api"
 	rsapi "github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/setup/base"
-	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dendrite/setup/jetstream"
 	"github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/dendrite/userapi/consumers"
@@ -33,16 +31,20 @@ import (
 	"github.com/matrix-org/dendrite/userapi/util"
 )
 
-// NewInternalAPI returns a concerete implementation of the internal API. Callers
+// NewInternalAPI returns a concrete implementation of the internal API. Callers
 // can call functions directly on the returned API or via an HTTP interface using AddInternalRoutes.
 func NewInternalAPI(
-	base *base.BaseDendrite, cfg *config.UserAPI,
-	appServices []config.ApplicationService, keyAPI keyapi.UserKeyAPI,
-	rsAPI rsapi.UserRoomserverAPI, pgClient pushgateway.Client,
-) api.UserInternalAPI {
+	base *base.BaseDendrite,
+	rsAPI rsapi.UserRoomserverAPI,
+	fedClient fedsenderapi.KeyserverFederationAPI,
+) *internal.UserInternalAPI {
+	cfg := &base.Cfg.UserAPI
 	js, _ := base.NATS.Prepare(base.ProcessContext, &cfg.Matrix.JetStream)
+	appServices := base.Cfg.Derived.ApplicationServices
 
-	db, err := storage.NewUserAPIDatabase(
+	pgClient := base.PushGatewayHTTPClient()
+
+	db, err := storage.NewUserDatabase(
 		base,
 		&cfg.AccountDatabase,
 		cfg.Matrix.ServerName,
@@ -55,6 +57,11 @@ func NewInternalAPI(
 		logrus.WithError(err).Panicf("failed to connect to accounts db")
 	}
 
+	keyDB, err := storage.NewKeyDatabase(base, &base.Cfg.KeyServer.Database)
+	if err != nil {
+		logrus.WithError(err).Panicf("failed to connect to key db")
+	}
+
 	syncProducer := producers.NewSyncAPI(
 		db, js,
 		// TODO: user API should handle syncs for account data. Right now,
@@ -64,17 +71,50 @@ func NewInternalAPI(
 		cfg.Matrix.JetStream.Prefixed(jetstream.OutputClientData),
 		cfg.Matrix.JetStream.Prefixed(jetstream.OutputNotificationData),
 	)
+	keyChangeProducer := &producers.KeyChange{
+		Topic:     cfg.Matrix.JetStream.Prefixed(jetstream.OutputKeyChangeEvent),
+		JetStream: js,
+		DB:        keyDB,
+	}
 
 	userAPI := &internal.UserInternalAPI{
 		DB:                   db,
+		KeyDatabase:          keyDB,
 		SyncProducer:         syncProducer,
+		KeyChangeProducer:    keyChangeProducer,
 		Config:               cfg,
 		AppServices:          appServices,
-		KeyAPI:               keyAPI,
 		RSAPI:                rsAPI,
 		DisableTLSValidation: cfg.PushGatewayDisableTLSValidation,
 		PgClient:             pgClient,
-		Cfg:                  cfg,
+		FedClient:            fedClient,
+	}
+
+	updater := internal.NewDeviceListUpdater(base.ProcessContext, keyDB, userAPI, keyChangeProducer, fedClient, 8, rsAPI, cfg.Matrix.ServerName) // 8 workers TODO: configurable
+	userAPI.Updater = updater
+	// Remove users which we don't share a room with anymore
+	if err := updater.CleanUp(); err != nil {
+		logrus.WithError(err).Error("failed to cleanup stale device lists")
+	}
+
+	go func() {
+		if err := updater.Start(); err != nil {
+			logrus.WithError(err).Panicf("failed to start device list updater")
+		}
+	}()
+
+	dlConsumer := consumers.NewDeviceListUpdateConsumer(
+		base.ProcessContext, cfg, js, updater,
+	)
+	if err := dlConsumer.Start(); err != nil {
+		logrus.WithError(err).Panic("failed to start device list consumer")
+	}
+
+	sigConsumer := consumers.NewSigningKeyUpdateConsumer(
+		base.ProcessContext, cfg, js, userAPI,
+	)
+	if err := sigConsumer.Start(); err != nil {
+		logrus.WithError(err).Panic("failed to start signing key consumer")
 	}
 
 	receiptConsumer := consumers.NewOutputReceiptEventConsumer(
diff --git a/userapi/userapi_test.go b/userapi/userapi_test.go
index 68d08c2f..08b1336b 100644
--- a/userapi/userapi_test.go
+++ b/userapi/userapi_test.go
@@ -21,7 +21,10 @@ import (
 	"testing"
 	"time"
 
+	"github.com/matrix-org/dendrite/userapi/producers"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/matrix-org/util"
+	"github.com/nats-io/nats.go"
 	"golang.org/x/crypto/bcrypt"
 
 	"github.com/matrix-org/dendrite/setup/config"
@@ -38,32 +41,55 @@ const (
 
 type apiTestOpts struct {
 	loginTokenLifetime time.Duration
+	serverName         string
 }
 
-func MustMakeInternalAPI(t *testing.T, opts apiTestOpts, dbType test.DBType) (api.UserInternalAPI, storage.Database, func()) {
+type dummyProducer struct{}
+
+func (d *dummyProducer) PublishMsg(*nats.Msg, ...nats.PubOpt) (*nats.PubAck, error) {
+	return &nats.PubAck{}, nil
+}
+
+func MustMakeInternalAPI(t *testing.T, opts apiTestOpts, dbType test.DBType) (api.UserInternalAPI, storage.UserDatabase, func()) {
 	if opts.loginTokenLifetime == 0 {
 		opts.loginTokenLifetime = api.DefaultLoginTokenLifetime * time.Millisecond
 	}
 	base, baseclose := testrig.CreateBaseDendrite(t, dbType)
 	connStr, close := test.PrepareDBConnectionString(t, dbType)
-	accountDB, err := storage.NewUserAPIDatabase(base, &config.DatabaseOptions{
+	sName := serverName
+	if opts.serverName != "" {
+		sName = gomatrixserverlib.ServerName(opts.serverName)
+	}
+	accountDB, err := storage.NewUserDatabase(base, &config.DatabaseOptions{
 		ConnectionString: config.DataSource(connStr),
-	}, serverName, bcrypt.MinCost, config.DefaultOpenIDTokenLifetimeMS, opts.loginTokenLifetime, "")
+	}, sName, bcrypt.MinCost, config.DefaultOpenIDTokenLifetimeMS, opts.loginTokenLifetime, "")
 	if err != nil {
 		t.Fatalf("failed to create account DB: %s", err)
 	}
 
+	keyDB, err := storage.NewKeyDatabase(base, &config.DatabaseOptions{
+		ConnectionString: config.DataSource(connStr),
+	})
+	if err != nil {
+		t.Fatalf("failed to create key DB: %s", err)
+	}
+
 	cfg := &config.UserAPI{
 		Matrix: &config.Global{
 			SigningIdentity: gomatrixserverlib.SigningIdentity{
-				ServerName: serverName,
+				ServerName: sName,
 			},
 		},
 	}
 
+	syncProducer := producers.NewSyncAPI(accountDB, &dummyProducer{}, "", "")
+	keyChangeProducer := &producers.KeyChange{DB: keyDB, JetStream: &dummyProducer{}}
 	return &internal.UserInternalAPI{
-			DB:     accountDB,
-			Config: cfg,
+			DB:                accountDB,
+			KeyDatabase:       keyDB,
+			Config:            cfg,
+			SyncProducer:      syncProducer,
+			KeyChangeProducer: keyChangeProducer,
 		}, accountDB, func() {
 			close()
 			baseclose()
@@ -332,3 +358,292 @@ func TestQueryAccountByLocalpart(t *testing.T) {
 		testCases(t, intAPI)
 	})
 }
+
+func TestAccountData(t *testing.T) {
+	ctx := context.Background()
+	alice := test.NewUser(t)
+
+	testCases := []struct {
+		name      string
+		inputData *api.InputAccountDataRequest
+		wantErr   bool
+	}{
+		{
+			name:      "not a local user",
+			inputData: &api.InputAccountDataRequest{UserID: "@notlocal:example.com"},
+			wantErr:   true,
+		},
+		{
+			name:      "local user missing datatype",
+			inputData: &api.InputAccountDataRequest{UserID: alice.ID},
+			wantErr:   true,
+		},
+		{
+			name:      "missing json",
+			inputData: &api.InputAccountDataRequest{UserID: alice.ID, DataType: "m.push_rules", AccountData: nil},
+			wantErr:   true,
+		},
+		{
+			name:      "with json",
+			inputData: &api.InputAccountDataRequest{UserID: alice.ID, DataType: "m.push_rules", AccountData: []byte("{}")},
+		},
+		{
+			name:      "room data",
+			inputData: &api.InputAccountDataRequest{UserID: alice.ID, DataType: "m.push_rules", AccountData: []byte("{}"), RoomID: "!dummy:test"},
+		},
+		{
+			name:      "ignored users",
+			inputData: &api.InputAccountDataRequest{UserID: alice.ID, DataType: "m.ignored_user_list", AccountData: []byte("{}")},
+		},
+		{
+			name:      "m.fully_read",
+			inputData: &api.InputAccountDataRequest{UserID: alice.ID, DataType: "m.fully_read", AccountData: []byte("{}")},
+		},
+	}
+
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		intAPI, _, close := MustMakeInternalAPI(t, apiTestOpts{serverName: "test"}, dbType)
+		defer close()
+
+		for _, tc := range testCases {
+			t.Run(tc.name, func(t *testing.T) {
+				res := api.InputAccountDataResponse{}
+				err := intAPI.InputAccountData(ctx, tc.inputData, &res)
+				if tc.wantErr && err == nil {
+					t.Fatalf("expected an error, but got none")
+				}
+				if !tc.wantErr && err != nil {
+					t.Fatalf("expected no error, but got: %s", err)
+				}
+
+				// query the data again and compare
+				queryRes := api.QueryAccountDataResponse{}
+				queryReq := api.QueryAccountDataRequest{
+					UserID:   tc.inputData.UserID,
+					DataType: tc.inputData.DataType,
+					RoomID:   tc.inputData.RoomID,
+				}
+				err = intAPI.QueryAccountData(ctx, &queryReq, &queryRes)
+				if err != nil && !tc.wantErr {
+					t.Fatal(err)
+				}
+				// verify global data
+				if tc.inputData.RoomID == "" {
+					if !reflect.DeepEqual(tc.inputData.AccountData, queryRes.GlobalAccountData[tc.inputData.DataType]) {
+						t.Fatalf("expected accountdata to be %s, got %s", string(tc.inputData.AccountData), string(queryRes.GlobalAccountData[tc.inputData.DataType]))
+					}
+				} else {
+					// verify room data
+					if !reflect.DeepEqual(tc.inputData.AccountData, queryRes.RoomAccountData[tc.inputData.RoomID][tc.inputData.DataType]) {
+						t.Fatalf("expected accountdata to be %s, got %s", string(tc.inputData.AccountData), string(queryRes.RoomAccountData[tc.inputData.RoomID][tc.inputData.DataType]))
+					}
+				}
+			})
+		}
+	})
+}
+
+func TestDevices(t *testing.T) {
+	ctx := context.Background()
+
+	dupeAccessToken := util.RandomString(8)
+
+	displayName := "testing"
+
+	creationTests := []struct {
+		name         string
+		inputData    *api.PerformDeviceCreationRequest
+		wantErr      bool
+		wantNewDevID bool
+	}{
+		{
+			name:      "not a local user",
+			inputData: &api.PerformDeviceCreationRequest{Localpart: "test1", ServerName: "notlocal"},
+			wantErr:   true,
+		},
+		{
+			name:      "implicit local user",
+			inputData: &api.PerformDeviceCreationRequest{Localpart: "test1", AccessToken: util.RandomString(8), NoDeviceListUpdate: true, DeviceDisplayName: &displayName},
+		},
+		{
+			name:      "explicit local user",
+			inputData: &api.PerformDeviceCreationRequest{Localpart: "test2", ServerName: "test", AccessToken: util.RandomString(8), NoDeviceListUpdate: true},
+		},
+		{
+			name:      "dupe token - ok",
+			inputData: &api.PerformDeviceCreationRequest{Localpart: "test3", ServerName: "test", AccessToken: dupeAccessToken, NoDeviceListUpdate: true},
+		},
+		{
+			name:      "dupe token - not ok",
+			inputData: &api.PerformDeviceCreationRequest{Localpart: "test3", ServerName: "test", AccessToken: dupeAccessToken, NoDeviceListUpdate: true},
+			wantErr:   true,
+		},
+		{
+			name:      "test3 second device", // used to test deletion later
+			inputData: &api.PerformDeviceCreationRequest{Localpart: "test3", ServerName: "test", AccessToken: util.RandomString(8), NoDeviceListUpdate: true},
+		},
+		{
+			name:         "test3 third device", // used to test deletion later
+			wantNewDevID: true,
+			inputData:    &api.PerformDeviceCreationRequest{Localpart: "test3", ServerName: "test", AccessToken: util.RandomString(8), NoDeviceListUpdate: true},
+		},
+	}
+
+	deletionTests := []struct {
+		name        string
+		inputData   *api.PerformDeviceDeletionRequest
+		wantErr     bool
+		wantDevices int
+	}{
+		{
+			name:      "deletion - not a local user",
+			inputData: &api.PerformDeviceDeletionRequest{UserID: "@test:notlocalhost"},
+			wantErr:   true,
+		},
+		{
+			name:        "deleting not existing devices should not error",
+			inputData:   &api.PerformDeviceDeletionRequest{UserID: "@test1:test", DeviceIDs: []string{"iDontExist"}},
+			wantDevices: 1,
+		},
+		{
+			name:        "delete all devices",
+			inputData:   &api.PerformDeviceDeletionRequest{UserID: "@test1:test"},
+			wantDevices: 0,
+		},
+		{
+			name:        "delete all devices",
+			inputData:   &api.PerformDeviceDeletionRequest{UserID: "@test3:test"},
+			wantDevices: 0,
+		},
+	}
+
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		intAPI, _, close := MustMakeInternalAPI(t, apiTestOpts{serverName: "test"}, dbType)
+		defer close()
+
+		for _, tc := range creationTests {
+			t.Run(tc.name, func(t *testing.T) {
+				res := api.PerformDeviceCreationResponse{}
+				deviceID := util.RandomString(8)
+				tc.inputData.DeviceID = &deviceID
+				if tc.wantNewDevID {
+					tc.inputData.DeviceID = nil
+				}
+				err := intAPI.PerformDeviceCreation(ctx, tc.inputData, &res)
+				if tc.wantErr && err == nil {
+					t.Fatalf("expected an error, but got none")
+				}
+				if !tc.wantErr && err != nil {
+					t.Fatalf("expected no error, but got: %s", err)
+				}
+				if !res.DeviceCreated {
+					return
+				}
+
+				queryDevicesRes := api.QueryDevicesResponse{}
+				queryDevicesReq := api.QueryDevicesRequest{UserID: res.Device.UserID}
+				if err = intAPI.QueryDevices(ctx, &queryDevicesReq, &queryDevicesRes); err != nil {
+					t.Fatal(err)
+				}
+				// We only want to verify one device
+				if len(queryDevicesRes.Devices) > 1 {
+					return
+				}
+				res.Device.AccessToken = ""
+
+				// At this point, there should only be one device
+				if !reflect.DeepEqual(*res.Device, queryDevicesRes.Devices[0]) {
+					t.Fatalf("expected device to be\n%#v, got \n%#v", *res.Device, queryDevicesRes.Devices[0])
+				}
+
+				newDisplayName := "new name"
+				if tc.inputData.DeviceDisplayName == nil {
+					updateRes := api.PerformDeviceUpdateResponse{}
+					updateReq := api.PerformDeviceUpdateRequest{
+						RequestingUserID: fmt.Sprintf("@%s:%s", tc.inputData.Localpart, "test"),
+						DeviceID:         deviceID,
+						DisplayName:      &newDisplayName,
+					}
+
+					if err = intAPI.PerformDeviceUpdate(ctx, &updateReq, &updateRes); err != nil {
+						t.Fatal(err)
+					}
+				}
+
+				queryDeviceInfosRes := api.QueryDeviceInfosResponse{}
+				queryDeviceInfosReq := api.QueryDeviceInfosRequest{DeviceIDs: []string{*tc.inputData.DeviceID}}
+				if err = intAPI.QueryDeviceInfos(ctx, &queryDeviceInfosReq, &queryDeviceInfosRes); err != nil {
+					t.Fatal(err)
+				}
+				gotDisplayName := queryDeviceInfosRes.DeviceInfo[*tc.inputData.DeviceID].DisplayName
+				if tc.inputData.DeviceDisplayName != nil {
+					wantDisplayName := *tc.inputData.DeviceDisplayName
+					if wantDisplayName != gotDisplayName {
+						t.Fatalf("expected displayName to be %s, got %s", wantDisplayName, gotDisplayName)
+					}
+				} else {
+					wantDisplayName := newDisplayName
+					if wantDisplayName != gotDisplayName {
+						t.Fatalf("expected displayName to be %s, got %s", wantDisplayName, gotDisplayName)
+					}
+				}
+			})
+		}
+
+		for _, tc := range deletionTests {
+			t.Run(tc.name, func(t *testing.T) {
+				delRes := api.PerformDeviceDeletionResponse{}
+				err := intAPI.PerformDeviceDeletion(ctx, tc.inputData, &delRes)
+				if tc.wantErr && err == nil {
+					t.Fatalf("expected an error, but got none")
+				}
+				if !tc.wantErr && err != nil {
+					t.Fatalf("expected no error, but got: %s", err)
+				}
+				if tc.wantErr {
+					return
+				}
+
+				queryDevicesRes := api.QueryDevicesResponse{}
+				queryDevicesReq := api.QueryDevicesRequest{UserID: tc.inputData.UserID}
+				if err = intAPI.QueryDevices(ctx, &queryDevicesReq, &queryDevicesRes); err != nil {
+					t.Fatal(err)
+				}
+
+				if len(queryDevicesRes.Devices) != tc.wantDevices {
+					t.Fatalf("expected %d devices, got %d", tc.wantDevices, len(queryDevicesRes.Devices))
+				}
+
+			})
+		}
+	})
+}
+
+// Tests that the session ID of a device is not reused when reusing the same device ID.
+func TestDeviceIDReuse(t *testing.T) {
+	ctx := context.Background()
+	test.WithAllDatabases(t, func(t *testing.T, dbType test.DBType) {
+		intAPI, _, close := MustMakeInternalAPI(t, apiTestOpts{serverName: "test"}, dbType)
+		defer close()
+
+		res := api.PerformDeviceCreationResponse{}
+		// create a first device
+		deviceID := util.RandomString(8)
+		req := api.PerformDeviceCreationRequest{Localpart: "alice", ServerName: "test", DeviceID: &deviceID, NoDeviceListUpdate: true}
+		err := intAPI.PerformDeviceCreation(ctx, &req, &res)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		// Do the same request again, we expect a different sessionID
+		res2 := api.PerformDeviceCreationResponse{}
+		err = intAPI.PerformDeviceCreation(ctx, &req, &res2)
+		if err != nil {
+			t.Fatalf("expected no error, but got: %v", err)
+		}
+
+		if res2.Device.SessionID == res.Device.SessionID {
+			t.Fatalf("expected a different session ID, but they are the same")
+		}
+	})
+}
diff --git a/userapi/util/devices.go b/userapi/util/devices.go
index c55fc799..31617d8c 100644
--- a/userapi/util/devices.go
+++ b/userapi/util/devices.go
@@ -19,7 +19,7 @@ type PusherDevice struct {
 }
 
 // GetPushDevices pushes to the configured devices of a local user.
-func GetPushDevices(ctx context.Context, localpart string, serverName gomatrixserverlib.ServerName, tweaks map[string]interface{}, db storage.Database) ([]*PusherDevice, error) {
+func GetPushDevices(ctx context.Context, localpart string, serverName gomatrixserverlib.ServerName, tweaks map[string]interface{}, db storage.UserDatabase) ([]*PusherDevice, error) {
 	pushers, err := db.GetPushers(ctx, localpart, serverName)
 	if err != nil {
 		return nil, fmt.Errorf("db.GetPushers: %w", err)
diff --git a/userapi/util/notify.go b/userapi/util/notify.go
index fc0ab39b..08d1371d 100644
--- a/userapi/util/notify.go
+++ b/userapi/util/notify.go
@@ -13,11 +13,11 @@ import (
 )
 
 // NotifyUserCountsAsync sends notifications to a local user's
-// notification destinations. Database lookups run synchronously, but
+// notification destinations. UserDatabase lookups run synchronously, but
 // a single goroutine is started when talking to the Push
 // gateways. There is no way to know when the background goroutine has
 // finished.
-func NotifyUserCountsAsync(ctx context.Context, pgClient pushgateway.Client, localpart string, serverName gomatrixserverlib.ServerName, db storage.Database) error {
+func NotifyUserCountsAsync(ctx context.Context, pgClient pushgateway.Client, localpart string, serverName gomatrixserverlib.ServerName, db storage.UserDatabase) error {
 	pusherDevices, err := GetPushDevices(ctx, localpart, serverName, nil, db)
 	if err != nil {
 		return err
diff --git a/userapi/util/notify_test.go b/userapi/util/notify_test.go
index f1d20259..421852d3 100644
--- a/userapi/util/notify_test.go
+++ b/userapi/util/notify_test.go
@@ -79,7 +79,7 @@ func TestNotifyUserCountsAsync(t *testing.T) {
 		defer close()
 		base, _, _ := testrig.Base(nil)
 		defer base.Close()
-		db, err := storage.NewUserAPIDatabase(base, &config.DatabaseOptions{
+		db, err := storage.NewUserDatabase(base, &config.DatabaseOptions{
 			ConnectionString: config.DataSource(connStr),
 		}, "test", bcrypt.MinCost, 0, 0, "")
 		if err != nil {
diff --git a/userapi/util/phonehomestats_test.go b/userapi/util/phonehomestats_test.go
index 6e62210e..5f626b5b 100644
--- a/userapi/util/phonehomestats_test.go
+++ b/userapi/util/phonehomestats_test.go
@@ -21,7 +21,7 @@ func TestCollect(t *testing.T) {
 		b, _, _ := testrig.Base(nil)
 		connStr, closeDB := test.PrepareDBConnectionString(t, dbType)
 		defer closeDB()
-		db, err := storage.NewUserAPIDatabase(b, &config.DatabaseOptions{
+		db, err := storage.NewUserDatabase(b, &config.DatabaseOptions{
 			ConnectionString: config.DataSource(connStr),
 		}, "localhost", bcrypt.MinCost, 1000, 1000, "")
 		if err != nil {