Merge bitcoin/bitcoin#28196: BIP324 connection support

db9888feec48c6220a2fcf92865503bbbdab02a4 net: detect wrong-network V1 talking to V2Transport (Pieter Wuille)
91e1ef8684997fb4b3e8b64ef3935a936445066b test: add unit tests for V2Transport (Pieter Wuille)
297c8889975a18258d6cc39b1ec1e94fed6630fb net: make V2Transport preallocate receive buffer space (Pieter Wuille)
3ffa5fb49ee4a6d9502aa957093bd94058630282 net: make V2Transport send uniformly random number garbage bytes (Pieter Wuille)
0be752d9f8ca27320bc3e82498c7640fabd7e8de net: add short message encoding/decoding support to V2Transport (Pieter Wuille)
8da8642062fa2c7aa2f49995b832c3d0897e37ed net: make V2Transport auto-detect incoming V1 and fall back to it (Pieter Wuille)
13a7f01557272db652b3f333af3f06af6897253f net: add V2Transport class with subset of BIP324 functionality (Pieter Wuille)
dc2d7eb810ef95b06620f334c198687579916435 crypto: Spanify EllSwiftPubKey constructor (Pieter Wuille)
5f4b2c6d79e81ee0445752ad558fcc17831f4b2f net: remove unused Transport::SetReceiveVersion (Pieter Wuille)
c3fad1f29df093e8fd03d70eb43f25ee9d531bf7 net: add have_next_message argument to Transport::GetBytesToSend() (Pieter Wuille)

Pull request description:

  This is part of #27634.

  This implements the BIP324 v2 transport (which implements all of what the BIP calls transport layer *and* application layer), though in a non-exposed way. It is tested through an extensive fuzz test, which verifies that v2 transports can talk to v2 transports, and v1 transports can talk to v2 transports, and a unit test that exercises a number of unusual scenarios. The transport is functionally complete, including:
  * Autodetection of incoming V1 connections.
  * Garbage, both sending and receiving.
  * Short message type IDs, both sending and receiving.
  * Ignore packets (receiving only, but tested in a unit test).
  * Session IDs are visible in `getpeerinfo` output (for manual comparison).

  Things that are not included, left for future PRs, are:
  * Actually using the v2 transport for connections.
  * Support for the `NODE_P2P_V2` service flag.
  * Retrying downgrade to V1 when attempted outbound V2 connections immediately fail.
  * P2P functional and unit tests

ACKs for top commit:
  naumenkogs:
    ACK db9888feec48c6220a2fcf92865503bbbdab02a4
  theStack:
    re-ACK db9888feec48c6220a2fcf92865503bbbdab02a4
  mzumsande:
    Code Review ACK db9888feec48c6220a2fcf92865503bbbdab02a4

Tree-SHA512: 8906ac1e733a99e1f31c9111055611f706d80bbfc2edf6a07fa6e47b21bb65baacd1ff17993cbbf588063b2f5ad30b3af674a50c7bc8e8ebf4671483a21bbfeb

5 files changed, 614 insertions, 22 deletions

diff --git a/src/test/bip324_tests.cpp b/src/test/bip324_tests.cpp
index 04472611ec..1ed7e23bcf 100644
--- a/src/test/bip324_tests.cpp
+++ b/src/test/bip324_tests.cpp
@@ -38,14 +38,8 @@ void TestBIP324PacketVector(
 {
     // Convert input from hex to char/byte vectors/arrays.
     const auto in_priv_ours = ParseHex(in_priv_ours_hex);
-    const auto in_ellswift_ours_vec = ParseHex<std::byte>(in_ellswift_ours_hex);
-    assert(in_ellswift_ours_vec.size() == 64);
-    std::array<std::byte, 64> in_ellswift_ours;
-    std::copy(in_ellswift_ours_vec.begin(), in_ellswift_ours_vec.end(), in_ellswift_ours.begin());
-    const auto in_ellswift_theirs_vec = ParseHex<std::byte>(in_ellswift_theirs_hex);
-    assert(in_ellswift_theirs_vec.size() == 64);
-    std::array<std::byte, 64> in_ellswift_theirs;
-    std::copy(in_ellswift_theirs_vec.begin(), in_ellswift_theirs_vec.end(), in_ellswift_theirs.begin());
+    const auto in_ellswift_ours = ParseHex<std::byte>(in_ellswift_ours_hex);
+    const auto in_ellswift_theirs = ParseHex<std::byte>(in_ellswift_theirs_hex);
     const auto in_contents = ParseHex<std::byte>(in_contents_hex);
     const auto in_aad = ParseHex<std::byte>(in_aad_hex);
     const auto mid_send_garbage = ParseHex<std::byte>(mid_send_garbage_hex);
diff --git a/src/test/denialofservice_tests.cpp b/src/test/denialofservice_tests.cpp
index 7f5d587cf6..8c1182b5e1 100644
--- a/src/test/denialofservice_tests.cpp
+++ b/src/test/denialofservice_tests.cpp
@@ -86,7 +86,7 @@ BOOST_AUTO_TEST_CASE(outbound_slow_chain_eviction)
 
     {
         LOCK(dummyNode1.cs_vSend);
-        const auto& [to_send, _more, _msg_type] = dummyNode1.m_transport->GetBytesToSend();
+        const auto& [to_send, _more, _msg_type] = dummyNode1.m_transport->GetBytesToSend(false);
         BOOST_CHECK(!to_send.empty());
     }
     connman.FlushSendBuffer(dummyNode1);
@@ -97,7 +97,7 @@ BOOST_AUTO_TEST_CASE(outbound_slow_chain_eviction)
     BOOST_CHECK(peerman.SendMessages(&dummyNode1)); // should result in getheaders
     {
         LOCK(dummyNode1.cs_vSend);
-        const auto& [to_send, _more, _msg_type] = dummyNode1.m_transport->GetBytesToSend();
+        const auto& [to_send, _more, _msg_type] = dummyNode1.m_transport->GetBytesToSend(false);
         BOOST_CHECK(!to_send.empty());
     }
     // Wait 3 more minutes
diff --git a/src/test/fuzz/p2p_transport_serialization.cpp b/src/test/fuzz/p2p_transport_serialization.cpp
index 2fa5de5008..6e3ef2a707 100644
--- a/src/test/fuzz/p2p_transport_serialization.cpp
+++ b/src/test/fuzz/p2p_transport_serialization.cpp
@@ -25,6 +25,7 @@ std::vector<std::string> g_all_messages;
 
 void initialize_p2p_transport_serialization()
 {
+    ECC_Start();
     SelectParams(ChainType::REGTEST);
     g_all_messages = getAllNetMessageTypes();
     std::sort(g_all_messages.begin(), g_all_messages.end());
@@ -92,7 +93,7 @@ FUZZ_TARGET(p2p_transport_serialization, .init = initialize_p2p_transport_serial
             assert(queued);
             std::optional<bool> known_more;
             while (true) {
-                const auto& [to_send, more, _msg_type] = send_transport.GetBytesToSend();
+                const auto& [to_send, more, _msg_type] = send_transport.GetBytesToSend(false);
                 if (known_more) assert(!to_send.empty() == *known_more);
                 if (to_send.empty()) break;
                 send_transport.MarkBytesSent(to_send.size());
@@ -124,11 +125,13 @@ void SimulationTest(Transport& initiator, Transport& responder, R& rng, FuzzedDa
     // Vectors with bytes last returned by GetBytesToSend() on transport[i].
     std::array<std::vector<uint8_t>, 2> to_send;
 
-    // Last returned 'more' values (if still relevant) by transport[i]->GetBytesToSend().
-    std::array<std::optional<bool>, 2> last_more;
+    // Last returned 'more' values (if still relevant) by transport[i]->GetBytesToSend(), for
+    // both have_next_message false and true.
+    std::array<std::optional<bool>, 2> last_more, last_more_next;
 
-    // Whether more bytes to be sent are expected on transport[i].
-    std::array<std::optional<bool>, 2> expect_more;
+    // Whether more bytes to be sent are expected on transport[i], before and after
+    // SetMessageToSend().
+    std::array<std::optional<bool>, 2> expect_more, expect_more_next;
 
     // Function to consume a message type.
     auto msg_type_fn = [&]() {
@@ -177,18 +180,27 @@ void SimulationTest(Transport& initiator, Transport& responder, R& rng, FuzzedDa
 
     // Wrapper around transport[i]->GetBytesToSend() that performs sanity checks.
     auto bytes_to_send_fn = [&](int side) -> Transport::BytesToSend {
-        const auto& [bytes, more, msg_type] = transports[side]->GetBytesToSend();
+        // Invoke GetBytesToSend twice (for have_next_message = {false, true}). This function does
+        // not modify state (it's const), and only the "more" return value should differ between
+        // the calls.
+        const auto& [bytes, more_nonext, msg_type] = transports[side]->GetBytesToSend(false);
+        const auto& [bytes_next, more_next, msg_type_next] = transports[side]->GetBytesToSend(true);
         // Compare with expected more.
         if (expect_more[side].has_value()) assert(!bytes.empty() == *expect_more[side]);
+        // Verify consistency between the two results.
+        assert(bytes == bytes_next);
+        assert(msg_type == msg_type_next);
+        if (more_nonext) assert(more_next);
         // Compare with previously reported output.
         assert(to_send[side].size() <= bytes.size());
         assert(to_send[side] == Span{bytes}.first(to_send[side].size()));
         to_send[side].resize(bytes.size());
         std::copy(bytes.begin(), bytes.end(), to_send[side].begin());
-        // Remember 'more' result.
-        last_more[side] = {more};
+        // Remember 'more' results.
+        last_more[side] = {more_nonext};
+        last_more_next[side] = {more_next};
         // Return.
-        return {bytes, more, msg_type};
+        return {bytes, more_nonext, msg_type};
     };
 
     // Function to make side send a new message.
@@ -199,7 +211,8 @@ void SimulationTest(Transport& initiator, Transport& responder, R& rng, FuzzedDa
         CSerializedNetMsg msg = next_msg[side].Copy();
         bool queued = transports[side]->SetMessageToSend(msg);
         // Update expected more data.
-        expect_more[side] = std::nullopt;
+        expect_more[side] = expect_more_next[side];
+        expect_more_next[side] = std::nullopt;
         // Verify consistency of GetBytesToSend after SetMessageToSend
         bytes_to_send_fn(/*side=*/side);
         if (queued) {
@@ -223,6 +236,7 @@ void SimulationTest(Transport& initiator, Transport& responder, R& rng, FuzzedDa
         // If all to-be-sent bytes were sent, move last_more data to expect_more data.
         if (send_now == bytes.size()) {
             expect_more[side] = last_more[side];
+            expect_more_next[side] = last_more_next[side];
         }
         // Remove the bytes from the last reported to-be-sent vector.
         assert(to_send[side].size() >= send_now);
@@ -251,6 +265,7 @@ void SimulationTest(Transport& initiator, Transport& responder, R& rng, FuzzedDa
             // Clear cached expected 'more' information: if certainly no more data was to be sent
             // before, receiving bytes makes this uncertain.
             if (expect_more[!side] == false) expect_more[!side] = std::nullopt;
+            if (expect_more_next[!side] == false) expect_more_next[!side] = std::nullopt;
             // Verify consistency of GetBytesToSend after ReceivedBytes
             bytes_to_send_fn(/*side=*/!side);
             bool progress = to_recv.size() < old_len;
@@ -320,6 +335,40 @@ std::unique_ptr<Transport> MakeV1Transport(NodeId nodeid) noexcept
     return std::make_unique<V1Transport>(nodeid, SER_NETWORK, INIT_PROTO_VERSION);
 }
 
+template<typename RNG>
+std::unique_ptr<Transport> MakeV2Transport(NodeId nodeid, bool initiator, RNG& rng, FuzzedDataProvider& provider)
+{
+    // Retrieve key
+    auto key = ConsumePrivateKey(provider);
+    if (!key.IsValid()) return {};
+    // Construct garbage
+    size_t garb_len = provider.ConsumeIntegralInRange<size_t>(0, V2Transport::MAX_GARBAGE_LEN);
+    std::vector<uint8_t> garb;
+    if (garb_len <= 64) {
+        // When the garbage length is up to 64 bytes, read it directly from the fuzzer input.
+        garb = provider.ConsumeBytes<uint8_t>(garb_len);
+        garb.resize(garb_len);
+    } else {
+        // If it's longer, generate it from the RNG. This avoids having large amounts of
+        // (hopefully) irrelevant data needing to be stored in the fuzzer data.
+        for (auto& v : garb) v = uint8_t(rng());
+    }
+    // Retrieve entropy
+    auto ent = provider.ConsumeBytes<std::byte>(32);
+    ent.resize(32);
+    // Use as entropy SHA256(ent || garbage). This prevents a situation where the fuzzer manages to
+    // include the garbage terminator (which is a function of both ellswift keys) in the garbage.
+    // This is extremely unlikely (~2^-116) with random keys/garbage, but the fuzzer can choose
+    // both non-randomly and dependently. Since the entropy is hashed anyway inside the ellswift
+    // computation, no coverage should be lost by using a hash as entropy, and it removes the
+    // possibility of garbage that happens to contain what is effectively a hash of the keys.
+    CSHA256().Write(UCharCast(ent.data()), ent.size())
+             .Write(garb.data(), garb.size())
+             .Finalize(UCharCast(ent.data()));
+
+    return std::make_unique<V2Transport>(nodeid, initiator, SER_NETWORK, INIT_PROTO_VERSION, key, ent, garb);
+}
+
 } // namespace
 
 FUZZ_TARGET(p2p_transport_bidirectional, .init = initialize_p2p_transport_serialization)
@@ -332,3 +381,25 @@ FUZZ_TARGET(p2p_transport_bidirectional, .init = initialize_p2p_transport_serial
     if (!t1 || !t2) return;
     SimulationTest(*t1, *t2, rng, provider);
 }
+
+FUZZ_TARGET(p2p_transport_bidirectional_v2, .init = initialize_p2p_transport_serialization)
+{
+    // Test with two V2 transports talking to each other.
+    FuzzedDataProvider provider{buffer.data(), buffer.size()};
+    XoRoShiRo128PlusPlus rng(provider.ConsumeIntegral<uint64_t>());
+    auto t1 = MakeV2Transport(NodeId{0}, true, rng, provider);
+    auto t2 = MakeV2Transport(NodeId{1}, false, rng, provider);
+    if (!t1 || !t2) return;
+    SimulationTest(*t1, *t2, rng, provider);
+}
+
+FUZZ_TARGET(p2p_transport_bidirectional_v1v2, .init = initialize_p2p_transport_serialization)
+{
+    // Test with a V1 initiator talking to a V2 responder.
+    FuzzedDataProvider provider{buffer.data(), buffer.size()};
+    XoRoShiRo128PlusPlus rng(provider.ConsumeIntegral<uint64_t>());
+    auto t1 = MakeV1Transport(NodeId{0});
+    auto t2 = MakeV2Transport(NodeId{1}, false, rng, provider);
+    if (!t1 || !t2) return;
+    SimulationTest(*t1, *t2, rng, provider);
+}
diff --git a/src/test/net_tests.cpp b/src/test/net_tests.cpp
index 295cb78b36..900e311d22 100644
--- a/src/test/net_tests.cpp
+++ b/src/test/net_tests.cpp
@@ -15,6 +15,7 @@
 #include <serialize.h>
 #include <span.h>
 #include <streams.h>
+#include <test/util/random.h>
 #include <test/util/setup_common.h>
 #include <test/util/validation.h>
 #include <timedata.h>
@@ -1005,4 +1006,530 @@ BOOST_AUTO_TEST_CASE(advertise_local_address)
     RemoveLocal(addr_cjdns);
 }
 
+namespace {
+
+/** A class for scenario-based tests of V2Transport
+ *
+ * Each V2TransportTester encapsulates a V2Transport (the one being tested), and can be told to
+ * interact with it. To do so, it also encapsulates a BIP324Cipher to act as the other side. A
+ * second V2Transport is not used, as doing so would not permit scenarios that involve sending
+ * invalid data, or ones scenarios using BIP324 features that are not implemented on the sending
+ * side (like decoy packets).
+ */
+class V2TransportTester
+{
+    V2Transport m_transport; //!< V2Transport being tested
+    BIP324Cipher m_cipher; //!< Cipher to help with the other side
+    bool m_test_initiator; //!< Whether m_transport is the initiator (true) or responder (false)
+
+    std::vector<uint8_t> m_sent_garbage; //!< The garbage we've sent to m_transport.
+    std::vector<uint8_t> m_to_send; //!< Bytes we have queued up to send to m_transport.
+    std::vector<uint8_t> m_received; //!< Bytes we have received from m_transport.
+    std::deque<CSerializedNetMsg> m_msg_to_send; //!< Messages to be sent *by* m_transport to us.
+
+public:
+    /** Construct a tester object. test_initiator: whether the tested transport is initiator. */
+    V2TransportTester(bool test_initiator) :
+        m_transport(0, test_initiator, SER_NETWORK, INIT_PROTO_VERSION),
+        m_test_initiator(test_initiator) {}
+
+    /** Data type returned by Interact:
+     *
+     * - std::nullopt: transport error occurred
+     * - otherwise: a vector of
+     *   - std::nullopt: invalid message received
+     *   - otherwise: a CNetMessage retrieved
+     */
+    using InteractResult = std::optional<std::vector<std::optional<CNetMessage>>>;
+
+    /** Send/receive scheduled/available bytes and messages.
+     *
+     * This is the only function that interacts with the transport being tested; everything else is
+     * scheduling things done by Interact(), or processing things learned by it.
+     */
+    InteractResult Interact()
+    {
+        std::vector<std::optional<CNetMessage>> ret;
+        while (true) {
+            bool progress{false};
+            // Send bytes from m_to_send to the transport.
+            if (!m_to_send.empty()) {
+                Span<const uint8_t> to_send = Span{m_to_send}.first(1 + InsecureRandRange(m_to_send.size()));
+                size_t old_len = to_send.size();
+                if (!m_transport.ReceivedBytes(to_send)) {
+                    return std::nullopt; // transport error occurred
+                }
+                if (old_len != to_send.size()) {
+                    progress = true;
+                    m_to_send.erase(m_to_send.begin(), m_to_send.begin() + (old_len - to_send.size()));
+                }
+            }
+            // Retrieve messages received by the transport.
+            if (m_transport.ReceivedMessageComplete() && (!progress || InsecureRandBool())) {
+                bool reject{false};
+                auto msg = m_transport.GetReceivedMessage({}, reject);
+                if (reject) {
+                    ret.push_back(std::nullopt);
+                } else {
+                    ret.push_back(std::move(msg));
+                }
+                progress = true;
+            }
+            // Enqueue a message to be sent by the transport to us.
+            if (!m_msg_to_send.empty() && (!progress || InsecureRandBool())) {
+                if (m_transport.SetMessageToSend(m_msg_to_send.front())) {
+                    m_msg_to_send.pop_front();
+                    progress = true;
+                }
+            }
+            // Receive bytes from the transport.
+            const auto& [recv_bytes, _more, _msg_type] = m_transport.GetBytesToSend(!m_msg_to_send.empty());
+            if (!recv_bytes.empty() && (!progress || InsecureRandBool())) {
+                size_t to_receive = 1 + InsecureRandRange(recv_bytes.size());
+                m_received.insert(m_received.end(), recv_bytes.begin(), recv_bytes.begin() + to_receive);
+                progress = true;
+                m_transport.MarkBytesSent(to_receive);
+            }
+            if (!progress) break;
+        }
+        return ret;
+    }
+
+    /** Expose the cipher. */
+    BIP324Cipher& GetCipher() { return m_cipher; }
+
+    /** Schedule bytes to be sent to the transport. */
+    void Send(Span<const uint8_t> data)
+    {
+        m_to_send.insert(m_to_send.end(), data.begin(), data.end());
+    }
+
+    /** Send V1 version message header to the transport. */
+    void SendV1Version(const CMessageHeader::MessageStartChars& magic)
+    {
+        CMessageHeader hdr(magic, "version", 126 + InsecureRandRange(11));
+        CDataStream ser(SER_NETWORK, CLIENT_VERSION);
+        ser << hdr;
+        m_to_send.insert(m_to_send.end(), UCharCast(ser.data()), UCharCast(ser.data() + ser.size()));
+    }
+
+    /** Schedule bytes to be sent to the transport. */
+    void Send(Span<const std::byte> data) { Send(MakeUCharSpan(data)); }
+
+    /** Schedule our ellswift key to be sent to the transport. */
+    void SendKey() { Send(m_cipher.GetOurPubKey()); }
+
+    /** Schedule specified garbage to be sent to the transport. */
+    void SendGarbage(Span<const uint8_t> garbage)
+    {
+        // Remember the specified garbage (so we can use it for constructing the garbage
+        // authentication packet).
+        m_sent_garbage.assign(garbage.begin(), garbage.end());
+        // Schedule it for sending.
+        Send(m_sent_garbage);
+    }
+
+    /** Schedule garbage (of specified length) to be sent to the transport. */
+    void SendGarbage(size_t garbage_len)
+    {
+        // Generate random garbage and send it.
+        SendGarbage(g_insecure_rand_ctx.randbytes<uint8_t>(garbage_len));
+    }
+
+    /** Schedule garbage (with valid random length) to be sent to the transport. */
+    void SendGarbage()
+    {
+         SendGarbage(InsecureRandRange(V2Transport::MAX_GARBAGE_LEN + 1));
+    }
+
+    /** Schedule a message to be sent to us by the transport. */
+    void AddMessage(std::string m_type, std::vector<uint8_t> payload)
+    {
+        CSerializedNetMsg msg;
+        msg.m_type = std::move(m_type);
+        msg.data = std::move(payload);
+        m_msg_to_send.push_back(std::move(msg));
+    }
+
+    /** Expect ellswift key to have been received from transport and process it.
+     *
+     * Many other V2TransportTester functions cannot be called until after ReceiveKey() has been
+     * called, as no encryption keys are set up before that point.
+     */
+    void ReceiveKey()
+    {
+        // When processing a key, enough bytes need to have been received already.
+        BOOST_REQUIRE(m_received.size() >= EllSwiftPubKey::size());
+        // Initialize the cipher using it (acting as the opposite side of the tested transport).
+        m_cipher.Initialize(MakeByteSpan(m_received).first(EllSwiftPubKey::size()), !m_test_initiator);
+        // Strip the processed bytes off the front of the receive buffer.
+        m_received.erase(m_received.begin(), m_received.begin() + EllSwiftPubKey::size());
+    }
+
+    /** Schedule an encrypted packet with specified content/aad/ignore to be sent to transport
+     *  (only after ReceiveKey). */
+    void SendPacket(Span<const uint8_t> content, Span<const uint8_t> aad = {}, bool ignore = false)
+    {
+        // Use cipher to construct ciphertext.
+        std::vector<std::byte> ciphertext;
+        ciphertext.resize(content.size() + BIP324Cipher::EXPANSION);
+        m_cipher.Encrypt(
+            /*contents=*/MakeByteSpan(content),
+            /*aad=*/MakeByteSpan(aad),
+            /*ignore=*/ignore,
+            /*output=*/ciphertext);
+        // Schedule it for sending.
+        Send(ciphertext);
+    }
+
+    /** Schedule garbage terminator and authentication packet to be sent to the transport (only
+     *  after ReceiveKey). */
+    void SendGarbageTermAuth(size_t garb_auth_data_len = 0, bool garb_auth_ignore = false)
+    {
+        // Generate random data to include in the garbage authentication packet (ignored by peer).
+        auto garb_auth_data = g_insecure_rand_ctx.randbytes<uint8_t>(garb_auth_data_len);
+        // Schedule the garbage terminator to be sent.
+        Send(m_cipher.GetSendGarbageTerminator());
+        // Schedule the garbage authentication packet to be sent.
+        SendPacket(/*content=*/garb_auth_data, /*aad=*/m_sent_garbage, /*ignore=*/garb_auth_ignore);
+    }
+
+    /** Schedule version packet to be sent to the transport (only after ReceiveKey). */
+    void SendVersion(Span<const uint8_t> version_data = {}, bool vers_ignore = false)
+    {
+        SendPacket(/*content=*/version_data, /*aad=*/{}, /*ignore=*/vers_ignore);
+    }
+
+    /** Expect a packet to have been received from transport, process it, and return its contents
+     *  (only after ReceiveKey). By default, decoys are skipped. */
+    std::vector<uint8_t> ReceivePacket(Span<const std::byte> aad = {}, bool skip_decoy = true)
+    {
+        std::vector<uint8_t> contents;
+        // Loop as long as there are ignored packets that are to be skipped.
+        while (true) {
+            // When processing a packet, at least enough bytes for its length descriptor must be received.
+            BOOST_REQUIRE(m_received.size() >= BIP324Cipher::LENGTH_LEN);
+            // Decrypt the content length.
+            size_t size = m_cipher.DecryptLength(MakeByteSpan(Span{m_received}.first(BIP324Cipher::LENGTH_LEN)));
+            // Check that the full packet is in the receive buffer.
+            BOOST_REQUIRE(m_received.size() >= size + BIP324Cipher::EXPANSION);
+            // Decrypt the packet contents.
+            contents.resize(size);
+            bool ignore{false};
+            bool ret = m_cipher.Decrypt(
+                /*input=*/MakeByteSpan(
+                    Span{m_received}.first(size + BIP324Cipher::EXPANSION).subspan(BIP324Cipher::LENGTH_LEN)),
+                /*aad=*/aad,
+                /*ignore=*/ignore,
+                /*contents=*/MakeWritableByteSpan(contents));
+            BOOST_CHECK(ret);
+            // Strip the processed packet's bytes off the front of the receive buffer.
+            m_received.erase(m_received.begin(), m_received.begin() + size + BIP324Cipher::EXPANSION);
+            // Stop if the ignore bit is not set on this packet, or if we choose to not honor it.
+            if (!ignore || !skip_decoy) break;
+        }
+        return contents;
+    }
+
+    /** Expect garbage, garbage terminator, and garbage auth packet to have been received, and
+     *  process them (only after ReceiveKey). */
+    void ReceiveGarbage()
+    {
+        // Figure out the garbage length.
+        size_t garblen;
+        for (garblen = 0; garblen <= V2Transport::MAX_GARBAGE_LEN; ++garblen) {
+            BOOST_REQUIRE(m_received.size() >= garblen + BIP324Cipher::GARBAGE_TERMINATOR_LEN);
+            auto term_span = MakeByteSpan(Span{m_received}.subspan(garblen, BIP324Cipher::GARBAGE_TERMINATOR_LEN));
+            if (term_span == m_cipher.GetReceiveGarbageTerminator()) break;
+        }
+        // Copy the garbage to a buffer.
+        std::vector<uint8_t> garbage(m_received.begin(), m_received.begin() + garblen);
+        // Strip garbage + garbage terminator off the front of the receive buffer.
+        m_received.erase(m_received.begin(), m_received.begin() + garblen + BIP324Cipher::GARBAGE_TERMINATOR_LEN);
+        // Process the expected garbage authentication packet. Such a packet still functions as one
+        // even when its ignore bit is set to true, so we do not skip decoy packets here.
+        ReceivePacket(/*aad=*/MakeByteSpan(garbage), /*skip_decoy=*/false);
+    }
+
+    /** Expect version packet to have been received, and process it (only after ReceiveKey). */
+    void ReceiveVersion()
+    {
+        auto contents = ReceivePacket();
+        // Version packets from real BIP324 peers are expected to be empty, despite the fact that
+        // this class supports *sending* non-empty version packets (to test that BIP324 peers
+        // correctly ignore version packet contents).
+        BOOST_CHECK(contents.empty());
+    }
+
+    /** Expect application packet to have been received, with specified short id and payload.
+     *  (only after ReceiveKey). */
+    void ReceiveMessage(uint8_t short_id, Span<const uint8_t> payload)
+    {
+        auto ret = ReceivePacket();
+        BOOST_CHECK(ret.size() == payload.size() + 1);
+        BOOST_CHECK(ret[0] == short_id);
+        BOOST_CHECK(Span{ret}.subspan(1) == payload);
+    }
+
+    /** Expect application packet to have been received, with specified 12-char message type and
+     *  payload (only after ReceiveKey). */
+    void ReceiveMessage(const std::string& m_type, Span<const uint8_t> payload)
+    {
+        auto ret = ReceivePacket();
+        BOOST_REQUIRE(ret.size() == payload.size() + 1 + CMessageHeader::COMMAND_SIZE);
+        BOOST_CHECK(ret[0] == 0);
+        for (unsigned i = 0; i < 12; ++i) {
+            if (i < m_type.size()) {
+                BOOST_CHECK(ret[1 + i] == m_type[i]);
+            } else {
+                BOOST_CHECK(ret[1 + i] == 0);
+            }
+        }
+        BOOST_CHECK(Span{ret}.subspan(1 + CMessageHeader::COMMAND_SIZE) == payload);
+    }
+
+    /** Schedule an encrypted packet with specified message type and payload to be sent to
+     *  transport (only after ReceiveKey). */
+    void SendMessage(std::string mtype, Span<const uint8_t> payload)
+    {
+        // Construct contents consisting of 0x00 + 12-byte message type + payload.
+        std::vector<uint8_t> contents(1 + CMessageHeader::COMMAND_SIZE + payload.size());
+        std::copy(mtype.begin(), mtype.end(), reinterpret_cast<char*>(contents.data() + 1));
+        std::copy(payload.begin(), payload.end(), contents.begin() + 1 + CMessageHeader::COMMAND_SIZE);
+        // Send a packet with that as contents.
+        SendPacket(contents);
+    }
+
+    /** Schedule an encrypted packet with specified short message id and payload to be sent to
+     *  transport (only after ReceiveKey). */
+    void SendMessage(uint8_t short_id, Span<const uint8_t> payload)
+    {
+        // Construct contents consisting of short_id + payload.
+        std::vector<uint8_t> contents(1 + payload.size());
+        contents[0] = short_id;
+        std::copy(payload.begin(), payload.end(), contents.begin() + 1);
+        // Send a packet with that as contents.
+        SendPacket(contents);
+    }
+
+    /** Introduce a bit error in the data scheduled to be sent. */
+    void Damage()
+    {
+        m_to_send[InsecureRandRange(m_to_send.size())] ^= (uint8_t{1} << InsecureRandRange(8));
+    }
+};
+
+} // namespace
+
+BOOST_AUTO_TEST_CASE(v2transport_test)
+{
+    // A mostly normal scenario, testing a transport in initiator mode.
+    for (int i = 0; i < 10; ++i) {
+        V2TransportTester tester(true);
+        auto ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.SendKey();
+        tester.SendGarbage();
+        tester.ReceiveKey();
+        tester.SendGarbageTermAuth();
+        tester.SendVersion();
+        ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.ReceiveGarbage();
+        tester.ReceiveVersion();
+        auto msg_data_1 = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandRange(100000));
+        auto msg_data_2 = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandRange(1000));
+        tester.SendMessage(uint8_t(4), msg_data_1); // cmpctblock short id
+        tester.SendMessage(0, {}); // Invalidly encoded message
+        tester.SendMessage("tx", msg_data_2); // 12-character encoded message type
+        ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->size() == 3);
+        BOOST_CHECK((*ret)[0] && (*ret)[0]->m_type == "cmpctblock" && Span{(*ret)[0]->m_recv} == MakeByteSpan(msg_data_1));
+        BOOST_CHECK(!(*ret)[1]);
+        BOOST_CHECK((*ret)[2] && (*ret)[2]->m_type == "tx" && Span{(*ret)[2]->m_recv} == MakeByteSpan(msg_data_2));
+
+        // Then send a message with a bit error, expecting failure.
+        tester.SendMessage("bad", msg_data_1);
+        tester.Damage();
+        ret = tester.Interact();
+        BOOST_CHECK(!ret);
+    }
+
+    // Normal scenario, with a transport in responder node.
+    for (int i = 0; i < 10; ++i) {
+        V2TransportTester tester(false);
+        tester.SendKey();
+        tester.SendGarbage();
+        auto ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.ReceiveKey();
+        tester.SendGarbageTermAuth();
+        tester.SendVersion();
+        ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.ReceiveGarbage();
+        tester.ReceiveVersion();
+        auto msg_data_1 = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandRange(100000));
+        auto msg_data_2 = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandRange(1000));
+        tester.SendMessage(uint8_t(14), msg_data_1); // inv short id
+        tester.SendMessage(uint8_t(19), msg_data_2); // pong short id
+        ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->size() == 2);
+        BOOST_CHECK((*ret)[0] && (*ret)[0]->m_type == "inv" && Span{(*ret)[0]->m_recv} == MakeByteSpan(msg_data_1));
+        BOOST_CHECK((*ret)[1] && (*ret)[1]->m_type == "pong" && Span{(*ret)[1]->m_recv} == MakeByteSpan(msg_data_2));
+
+        // Then send a too-large message.
+        auto msg_data_3 = g_insecure_rand_ctx.randbytes<uint8_t>(4005000);
+        tester.SendMessage(uint8_t(11), msg_data_3); // getdata short id
+        ret = tester.Interact();
+        BOOST_CHECK(!ret);
+    }
+
+    // Various valid but unusual scenarios.
+    for (int i = 0; i < 50; ++i) {
+        /** Whether an initiator or responder is being tested. */
+        bool initiator = InsecureRandBool();
+        /** Use either 0 bytes or the maximum possible (4095 bytes) garbage length. */
+        size_t garb_len = InsecureRandBool() ? 0 : V2Transport::MAX_GARBAGE_LEN;
+        /** Sometimes, use non-empty contents in the garbage authentication packet (which is to be ignored). */
+        size_t garb_auth_data_len = InsecureRandBool() ? 0 : InsecureRandRange(100000);
+        /** Whether to set the ignore bit on the garbage authentication packet (it still functions as garbage authentication). */
+        bool garb_ignore = InsecureRandBool();
+        /** How many decoy packets to send before the version packet. */
+        unsigned num_ignore_version = InsecureRandRange(10);
+        /** What data to send in the version packet (ignored by BIP324 peers, but reserved for future extensions). */
+        auto ver_data = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandBool() ? 0 : InsecureRandRange(1000));
+        /** Whether to immediately send key and garbage out (required for responders, optional otherwise). */
+        bool send_immediately = !initiator || InsecureRandBool();
+        /** How many decoy packets to send before the first and second real message. */
+        unsigned num_decoys_1 = InsecureRandRange(1000), num_decoys_2 = InsecureRandRange(1000);
+        V2TransportTester tester(initiator);
+        if (send_immediately) {
+            tester.SendKey();
+            tester.SendGarbage(garb_len);
+        }
+        auto ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        if (!send_immediately) {
+            tester.SendKey();
+            tester.SendGarbage(garb_len);
+        }
+        tester.ReceiveKey();
+        tester.SendGarbageTermAuth(garb_auth_data_len, garb_ignore);
+        for (unsigned v = 0; v < num_ignore_version; ++v) {
+            size_t ver_ign_data_len = InsecureRandBool() ? 0 : InsecureRandRange(1000);
+            auto ver_ign_data = g_insecure_rand_ctx.randbytes<uint8_t>(ver_ign_data_len);
+            tester.SendVersion(ver_ign_data, true);
+        }
+        tester.SendVersion(ver_data, false);
+        ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.ReceiveGarbage();
+        tester.ReceiveVersion();
+        for (unsigned d = 0; d < num_decoys_1; ++d) {
+            auto decoy_data = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandRange(1000));
+            tester.SendPacket(/*content=*/decoy_data, /*aad=*/{}, /*ignore=*/true);
+        }
+        auto msg_data_1 = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandRange(4000000));
+        tester.SendMessage(uint8_t(28), msg_data_1);
+        for (unsigned d = 0; d < num_decoys_2; ++d) {
+            auto decoy_data = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandRange(1000));
+            tester.SendPacket(/*content=*/decoy_data, /*aad=*/{}, /*ignore=*/true);
+        }
+        auto msg_data_2 = g_insecure_rand_ctx.randbytes<uint8_t>(InsecureRandRange(1000));
+        tester.SendMessage(uint8_t(13), msg_data_2); // headers short id
+        // Send invalidly-encoded message
+        tester.SendMessage(std::string("blocktxn\x00\x00\x00a", CMessageHeader::COMMAND_SIZE), {});
+        tester.SendMessage("foobar", {}); // test receiving unknown message type
+        tester.AddMessage("barfoo", {}); // test sending unknown message type
+        ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->size() == 4);
+        BOOST_CHECK((*ret)[0] && (*ret)[0]->m_type == "addrv2" && Span{(*ret)[0]->m_recv} == MakeByteSpan(msg_data_1));
+        BOOST_CHECK((*ret)[1] && (*ret)[1]->m_type == "headers" && Span{(*ret)[1]->m_recv} == MakeByteSpan(msg_data_2));
+        BOOST_CHECK(!(*ret)[2]);
+        BOOST_CHECK((*ret)[3] && (*ret)[3]->m_type == "foobar" && (*ret)[3]->m_recv.empty());
+        tester.ReceiveMessage("barfoo", {});
+    }
+
+    // Too long garbage (initiator).
+    {
+        V2TransportTester tester(true);
+        auto ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.SendKey();
+        tester.SendGarbage(V2Transport::MAX_GARBAGE_LEN + 1);
+        tester.ReceiveKey();
+        tester.SendGarbageTermAuth();
+        ret = tester.Interact();
+        BOOST_CHECK(!ret);
+    }
+
+    // Too long garbage (responder).
+    {
+        V2TransportTester tester(false);
+        tester.SendKey();
+        tester.SendGarbage(V2Transport::MAX_GARBAGE_LEN + 1);
+        auto ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.ReceiveKey();
+        tester.SendGarbageTermAuth();
+        ret = tester.Interact();
+        BOOST_CHECK(!ret);
+    }
+
+    // Send garbage that includes the first 15 garbage terminator bytes somewhere.
+    {
+        V2TransportTester tester(true);
+        auto ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.SendKey();
+        tester.ReceiveKey();
+        /** The number of random garbage bytes before the included first 15 bytes of terminator. */
+        size_t len_before = InsecureRandRange(V2Transport::MAX_GARBAGE_LEN - 16 + 1);
+        /** The number of random garbage bytes after it. */
+        size_t len_after = InsecureRandRange(V2Transport::MAX_GARBAGE_LEN - 16 - len_before + 1);
+        // Construct len_before + 16 + len_after random bytes.
+        auto garbage = g_insecure_rand_ctx.randbytes<uint8_t>(len_before + 16 + len_after);
+        // Replace the designed 16 bytes in the middle with the to-be-sent garbage terminator.
+        auto garb_term = MakeUCharSpan(tester.GetCipher().GetSendGarbageTerminator());
+        std::copy(garb_term.begin(), garb_term.begin() + 16, garbage.begin() + len_before);
+        // Introduce a bit error in the last byte of that copied garbage terminator, making only
+        // the first 15 of them match.
+        garbage[len_before + 15] ^= (uint8_t(1) << InsecureRandRange(8));
+        tester.SendGarbage(garbage);
+        tester.SendGarbageTermAuth();
+        tester.SendVersion();
+        ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->empty());
+        tester.ReceiveGarbage();
+        tester.ReceiveVersion();
+        auto msg_data_1 = g_insecure_rand_ctx.randbytes<uint8_t>(4000000); // test that receiving 4M payload works
+        auto msg_data_2 = g_insecure_rand_ctx.randbytes<uint8_t>(4000000); // test that sending 4M payload works
+        tester.SendMessage(uint8_t(InsecureRandRange(223) + 33), {}); // unknown short id
+        tester.SendMessage(uint8_t(2), msg_data_1); // "block" short id
+        tester.AddMessage("blocktxn", msg_data_2); // schedule blocktxn to be sent to us
+        ret = tester.Interact();
+        BOOST_REQUIRE(ret && ret->size() == 2);
+        BOOST_CHECK(!(*ret)[0]);
+        BOOST_CHECK((*ret)[1] && (*ret)[1]->m_type == "block" && Span{(*ret)[1]->m_recv} == MakeByteSpan(msg_data_1));
+        tester.ReceiveMessage(uint8_t(3), msg_data_2); // "blocktxn" short id
+    }
+
+    // Send correct network's V1 header
+    {
+        V2TransportTester tester(false);
+        tester.SendV1Version(Params().MessageStart());
+        auto ret = tester.Interact();
+        BOOST_CHECK(ret);
+    }
+
+    // Send wrong network's V1 header
+    {
+        V2TransportTester tester(false);
+        tester.SendV1Version(CChainParams::Main()->MessageStart());
+        auto ret = tester.Interact();
+        BOOST_CHECK(!ret);
+    }
+}
+
 BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/util/net.cpp b/src/test/util/net.cpp
index 5696f8d13c..dc64c0b4c1 100644
--- a/src/test/util/net.cpp
+++ b/src/test/util/net.cpp
@@ -78,7 +78,7 @@ void ConnmanTestMsg::FlushSendBuffer(CNode& node) const
     node.vSendMsg.clear();
     node.m_send_memusage = 0;
     while (true) {
-        const auto& [to_send, _more, _msg_type] = node.m_transport->GetBytesToSend();
+        const auto& [to_send, _more, _msg_type] = node.m_transport->GetBytesToSend(false);
         if (to_send.empty()) break;
         node.m_transport->MarkBytesSent(to_send.size());
     }
@@ -90,7 +90,7 @@ bool ConnmanTestMsg::ReceiveMsgFrom(CNode& node, CSerializedNetMsg&& ser_msg) co
     assert(queued);
     bool complete{false};
     while (true) {
-        const auto& [to_send, _more, _msg_type] = node.m_transport->GetBytesToSend();
+        const auto& [to_send, _more, _msg_type] = node.m_transport->GetBytesToSend(false);
         if (to_send.empty()) break;
         NodeReceiveMsgBytes(node, to_send, complete);
         node.m_transport->MarkBytesSent(to_send.size());