Merge #13557: BIP 174 PSBT Serializations and RPCs

020628e3a4e88e36647eaf92bac4b3552796ac6a Tests for PSBT (Andrew Chow)
a4b06fb42eb0ad94e562ca839391b57e69285136 Create wallet RPCs for PSBT (Andrew Chow)
c27fe419efb3b6588c400d764122ffb33375e028 Create utility RPCs for PSBT (Andrew Chow)
8b5ef2793748065727a9a2498805ae5b269dcb4f SignPSBTInput wrapper function (Andrew Chow)
58a8e28918025c28f19ba19cbaa4a72374162942 Refactor transaction creation and transaction funding logic (Andrew Chow)
e9d86a43ad8b1ab83b324e9a7a64c43a61337501 Methods for interacting with PSBT structs (Andrew Chow)
12bcc64f277f642ece03c25653e726f2276f0d51 Add pubkeys and whether input was witness to SignatureData (Andrew Chow)
41c607f09badb2c3ed58ff6fb17a8ebbef2cdabd Implement PSBT Structures and un/serialization methods per BIP 174 (Andrew Chow)

Pull request description:

  This Pull Request fully implements the [updated](https://github.com/bitcoin/bips/pull/694) BIP 174 specification. It is based upon #13425 which implements the majority of the signing logic.

  BIP 174 specifies a binary transaction format which contains the information necessary for a signer to produce signatures for the transaction and holds the signatures for an input while the input does not have a complete set of signatures.

  This PR contains structs for PSBT, serialization, and deserialzation code. Some changes to `SignatureData` have been made to support detection of UTXO type and storing public keys.

  ***

  Many RPCs have been added to handle PSBTs.

  `walletprocesspsbt` takes a PSBT format transaction, updates the PSBT with any inputs related to this wallet, signs, and finalizes the transaction. There is also an option to not sign and just update.

  `walletcreatefundedpsbt` creates a PSBT from user provided data in the same form as createrawtransaction. It also funds the transaction and takes an options argument in the same form as `fundrawtransaction`. The resulting PSBT is blank with no input or output data filled in. It is analogous to a combination of `createrawtransaction` and `fundrawtransaction`

  `decodepsbt` takes a PSBT and decodes it to JSON. It is analogous to `decoderawtransaction`

  `combinepsbt` takes multiple PSBTs for the same tx and combines them. It is analogous to `combinerawtransaction`

  `finalizepsbt` takes a PSBT and finalizes the inputs. If all inputs are final, it extracts the network serialized transaction and returns that instead of a PSBT unless instructed otherwise.

  `createpsbt` is like `createrawtransaction` but for PSBTs instead of raw transactions.

  `convertpsbt` takes a network serialized transaction and converts it into a psbt. The resulting psbt will lose all signature data and an explicit flag must be set to allow transactions with signature data to be converted.

  ***

  This supersedes #12136

Tree-SHA512: 1ac7a79e5bc669933f0a6fcc93ded55263fdde9e8c144a30266b13ef9f62aacf43edd4cbca1ffbe003090b067e9643c9298c79be69d7c1b10231b32acafb6338

2 files changed, 766 insertions, 3 deletions

diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index 60a8a2655d..f1ac1f411a 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -49,9 +49,10 @@ static bool GetCScript(const SigningProvider& provider, const SignatureData& sig
     return false;
 }
 
-static bool GetPubKey(const SigningProvider& provider, const SignatureData& sigdata, const CKeyID& address, CPubKey& pubkey)
+static bool GetPubKey(const SigningProvider& provider, SignatureData& sigdata, const CKeyID& address, CPubKey& pubkey)
 {
     if (provider.GetPubKey(address, pubkey)) {
+        sigdata.misc_pubkeys.emplace(pubkey.GetID(), pubkey);
         return true;
     }
     // Look for pubkey in all partial sigs
@@ -60,6 +61,12 @@ static bool GetPubKey(const SigningProvider& provider, const SignatureData& sigd
         pubkey = it->second.first;
         return true;
     }
+    // Look for pubkey in pubkey list
+    const auto& pk_it = sigdata.misc_pubkeys.find(address);
+    if (pk_it != sigdata.misc_pubkeys.end()) {
+        pubkey = pk_it->second;
+        return true;
+    }
     return false;
 }
 
@@ -70,9 +77,9 @@ static bool CreateSig(const BaseSignatureCreator& creator, SignatureData& sigdat
         sig_out = it->second.second;
         return true;
     }
+    CPubKey pubkey;
+    GetPubKey(provider, sigdata, keyid, pubkey);
     if (creator.CreateSig(provider, sig_out, keyid, scriptcode, sigversion)) {
-        CPubKey pubkey;
-        GetPubKey(provider, sigdata, keyid, pubkey);
         auto i = sigdata.signatures.emplace(keyid, SigPair(pubkey, sig_out));
         assert(i.second);
         return true;
@@ -200,6 +207,7 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
         txnouttype subType;
         solved = solved && SignStep(provider, creator, witnessscript, result, subType, SigVersion::WITNESS_V0, sigdata);
         sigdata.scriptWitness.stack = result;
+        sigdata.witness = true;
         result.clear();
     }
     else if (solved && whichType == TX_WITNESS_V0_SCRIPTHASH)
@@ -210,7 +218,10 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
         solved = solved && SignStep(provider, creator, witnessscript, result, subType, SigVersion::WITNESS_V0, sigdata) && subType != TX_SCRIPTHASH && subType != TX_WITNESS_V0_SCRIPTHASH && subType != TX_WITNESS_V0_KEYHASH;
         result.push_back(std::vector<unsigned char>(witnessscript.begin(), witnessscript.end()));
         sigdata.scriptWitness.stack = result;
+        sigdata.witness = true;
         result.clear();
+    } else if (solved && whichType == TX_WITNESS_UNKNOWN) {
+        sigdata.witness = true;
     }
 
     if (P2SH) {
@@ -223,6 +234,32 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
     return sigdata.complete;
 }
 
+bool SignPSBTInput(const SigningProvider& provider, const CMutableTransaction& tx, PSBTInput& input, SignatureData& sigdata, int index, int sighash)
+{
+    // if this input has a final scriptsig or scriptwitness, don't do anything with it
+    if (!input.final_script_sig.empty() || !input.final_script_witness.IsNull()) {
+        return true;
+    }
+
+    // Fill SignatureData with input info
+    input.FillSignatureData(sigdata);
+
+    // Get UTXO
+    CTxOut utxo;
+    if (input.non_witness_utxo) {
+        utxo = input.non_witness_utxo->vout[tx.vin[index].prevout.n];
+    } else if (!input.witness_utxo.IsNull()) {
+        utxo = input.witness_utxo;
+    } else {
+        return false;
+    }
+
+    MutableTransactionSignatureCreator creator(&tx, index, utxo.nValue, sighash);
+    bool sig_complete = ProduceSignature(provider, creator, utxo.scriptPubKey, sigdata);
+    input.FromSignatureData(sigdata);
+    return sig_complete;
+}
+
 class SignatureExtractorChecker final : public BaseSignatureChecker
 {
 private:
@@ -429,3 +466,161 @@ bool IsSolvable(const SigningProvider& provider, const CScript& script)
     }
     return false;
 }
+
+
+bool PartiallySignedTransaction::IsNull() const
+{
+    return !tx && inputs.empty() && outputs.empty() && unknown.empty();
+}
+
+void PartiallySignedTransaction::Merge(const PartiallySignedTransaction& psbt)
+{
+    for (unsigned int i = 0; i < inputs.size(); ++i) {
+        inputs[i].Merge(psbt.inputs[i]);
+    }
+    for (unsigned int i = 0; i < outputs.size(); ++i) {
+        outputs[i].Merge(psbt.outputs[i]);
+    }
+}
+
+bool PartiallySignedTransaction::IsSane() const
+{
+    for (PSBTInput input : inputs) {
+        if (!input.IsSane()) return false;
+    }
+    return true;
+}
+
+bool PSBTInput::IsNull() const
+{
+    return !non_witness_utxo && witness_utxo.IsNull() && partial_sigs.empty() && unknown.empty() && hd_keypaths.empty() && redeem_script.empty() && witness_script.empty();
+}
+
+void PSBTInput::FillSignatureData(SignatureData& sigdata) const
+{
+    if (!final_script_sig.empty()) {
+        sigdata.scriptSig = final_script_sig;
+        sigdata.complete = true;
+    }
+    if (!final_script_witness.IsNull()) {
+        sigdata.scriptWitness = final_script_witness;
+        sigdata.complete = true;
+    }
+    if (sigdata.complete) {
+        return;
+    }
+
+    sigdata.signatures.insert(partial_sigs.begin(), partial_sigs.end());
+    if (!redeem_script.empty()) {
+        sigdata.redeem_script = redeem_script;
+    }
+    if (!witness_script.empty()) {
+        sigdata.witness_script = witness_script;
+    }
+    for (const auto& key_pair : hd_keypaths) {
+        sigdata.misc_pubkeys.emplace(key_pair.first.GetID(), key_pair.first);
+    }
+}
+
+void PSBTInput::FromSignatureData(const SignatureData& sigdata)
+{
+    if (sigdata.complete) {
+        partial_sigs.clear();
+        hd_keypaths.clear();
+        redeem_script.clear();
+        witness_script.clear();
+
+        if (!sigdata.scriptSig.empty()) {
+            final_script_sig = sigdata.scriptSig;
+        }
+        if (!sigdata.scriptWitness.IsNull()) {
+            final_script_witness = sigdata.scriptWitness;
+        }
+        return;
+    }
+
+    partial_sigs.insert(sigdata.signatures.begin(), sigdata.signatures.end());
+    if (redeem_script.empty() && !sigdata.redeem_script.empty()) {
+        redeem_script = sigdata.redeem_script;
+    }
+    if (witness_script.empty() && !sigdata.witness_script.empty()) {
+        witness_script = sigdata.witness_script;
+    }
+}
+
+void PSBTInput::Merge(const PSBTInput& input)
+{
+    if (!non_witness_utxo && input.non_witness_utxo) non_witness_utxo = input.non_witness_utxo;
+    if (witness_utxo.IsNull() && !input.witness_utxo.IsNull()) {
+        witness_utxo = input.witness_utxo;
+        non_witness_utxo = nullptr; // Clear out any non-witness utxo when we set a witness one.
+    }
+
+    partial_sigs.insert(input.partial_sigs.begin(), input.partial_sigs.end());
+    hd_keypaths.insert(input.hd_keypaths.begin(), input.hd_keypaths.end());
+    unknown.insert(input.unknown.begin(), input.unknown.end());
+
+    if (redeem_script.empty() && !input.redeem_script.empty()) redeem_script = input.redeem_script;
+    if (witness_script.empty() && !input.witness_script.empty()) witness_script = input.witness_script;
+    if (final_script_sig.empty() && !input.final_script_sig.empty()) final_script_sig = input.final_script_sig;
+    if (final_script_witness.IsNull() && !input.final_script_witness.IsNull()) final_script_witness = input.final_script_witness;
+}
+
+bool PSBTInput::IsSane() const
+{
+    // Cannot have both witness and non-witness utxos
+    if (!witness_utxo.IsNull() && non_witness_utxo) return false;
+
+    // If we have a witness_script or a scriptWitness, we must also have a witness utxo
+    if (!witness_script.empty() && witness_utxo.IsNull()) return false;
+    if (!final_script_witness.IsNull() && witness_utxo.IsNull()) return false;
+
+    return true;
+}
+
+void PSBTOutput::FillSignatureData(SignatureData& sigdata) const
+{
+    if (!redeem_script.empty()) {
+        sigdata.redeem_script = redeem_script;
+    }
+    if (!witness_script.empty()) {
+        sigdata.witness_script = witness_script;
+    }
+    for (const auto& key_pair : hd_keypaths) {
+        sigdata.misc_pubkeys.emplace(key_pair.first.GetID(), key_pair.first);
+    }
+}
+
+void PSBTOutput::FromSignatureData(const SignatureData& sigdata)
+{
+    if (redeem_script.empty() && !sigdata.redeem_script.empty()) {
+        redeem_script = sigdata.redeem_script;
+    }
+    if (witness_script.empty() && !sigdata.witness_script.empty()) {
+        witness_script = sigdata.witness_script;
+    }
+}
+
+bool PSBTOutput::IsNull() const
+{
+    return redeem_script.empty() && witness_script.empty() && hd_keypaths.empty() && unknown.empty();
+}
+
+void PSBTOutput::Merge(const PSBTOutput& output)
+{
+    hd_keypaths.insert(output.hd_keypaths.begin(), output.hd_keypaths.end());
+    unknown.insert(output.unknown.begin(), output.unknown.end());
+
+    if (redeem_script.empty() && !output.redeem_script.empty()) redeem_script = output.redeem_script;
+    if (witness_script.empty() && !output.witness_script.empty()) witness_script = output.witness_script;
+}
+
+bool PublicOnlySigningProvider::GetCScript(const CScriptID &scriptid, CScript& script) const
+{
+    return m_provider->GetCScript(scriptid, script);
+}
+
+bool PublicOnlySigningProvider::GetPubKey(const CKeyID &address, CPubKey& pubkey) const
+{
+    return m_provider->GetPubKey(address, pubkey);
+}
diff --git a/src/script/sign.h b/src/script/sign.h
index 3666859641..e3a6196b28 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -6,7 +6,11 @@
 #ifndef BITCOIN_SCRIPT_SIGN_H
 #define BITCOIN_SCRIPT_SIGN_H
 
+#include <boost/optional.hpp>
+#include <hash.h>
+#include <pubkey.h>
 #include <script/interpreter.h>
+#include <streams.h>
 
 class CKey;
 class CKeyID;
@@ -28,6 +32,17 @@ public:
 
 extern const SigningProvider& DUMMY_SIGNING_PROVIDER;
 
+class PublicOnlySigningProvider : public SigningProvider
+{
+private:
+    const SigningProvider* m_provider;
+
+public:
+    PublicOnlySigningProvider(const SigningProvider* provider) : m_provider(provider) {}
+    bool GetCScript(const CScriptID &scriptid, CScript& script) const;
+    bool GetPubKey(const CKeyID &address, CPubKey& pubkey) const;
+};
+
 /** Interface for signature creators. */
 class BaseSignatureCreator {
 public:
@@ -62,17 +77,567 @@ typedef std::pair<CPubKey, std::vector<unsigned char>> SigPair;
 // in order to construct final scriptSigs and scriptWitnesses.
 struct SignatureData {
     bool complete = false; ///< Stores whether the scriptSig and scriptWitness are complete
+    bool witness = false; ///< Stores whether the input this SigData corresponds to is a witness input
     CScript scriptSig; ///< The scriptSig of an input. Contains complete signatures or the traditional partial signatures format
     CScript redeem_script; ///< The redeemScript (if any) for the input
     CScript witness_script; ///< The witnessScript (if any) for the input. witnessScripts are used in P2WSH outputs.
     CScriptWitness scriptWitness; ///< The scriptWitness of an input. Contains complete signatures or the traditional partial signatures format. scriptWitness is part of a transaction input per BIP 144.
     std::map<CKeyID, SigPair> signatures; ///< BIP 174 style partial signatures for the input. May contain all signatures necessary for producing a final scriptSig or scriptWitness.
+    std::map<CKeyID, CPubKey> misc_pubkeys;
 
     SignatureData() {}
     explicit SignatureData(const CScript& script) : scriptSig(script) {}
     void MergeSignatureData(SignatureData sigdata);
 };
 
+// Magic bytes
+static constexpr uint8_t PSBT_MAGIC_BYTES[5] = {'p', 's', 'b', 't', 0xff};
+
+// Global types
+static constexpr uint8_t PSBT_GLOBAL_UNSIGNED_TX = 0x00;
+
+// Input types
+static constexpr uint8_t PSBT_IN_NON_WITNESS_UTXO = 0x00;
+static constexpr uint8_t PSBT_IN_WITNESS_UTXO = 0x01;
+static constexpr uint8_t PSBT_IN_PARTIAL_SIG = 0x02;
+static constexpr uint8_t PSBT_IN_SIGHASH = 0x03;
+static constexpr uint8_t PSBT_IN_REDEEMSCRIPT = 0x04;
+static constexpr uint8_t PSBT_IN_WITNESSSCRIPT = 0x05;
+static constexpr uint8_t PSBT_IN_BIP32_DERIVATION = 0x06;
+static constexpr uint8_t PSBT_IN_SCRIPTSIG = 0x07;
+static constexpr uint8_t PSBT_IN_SCRIPTWITNESS = 0x08;
+
+// Output types
+static constexpr uint8_t PSBT_OUT_REDEEMSCRIPT = 0x00;
+static constexpr uint8_t PSBT_OUT_WITNESSSCRIPT = 0x01;
+static constexpr uint8_t PSBT_OUT_BIP32_DERIVATION = 0x02;
+
+// The separator is 0x00. Reading this in means that the unserializer can interpret it
+// as a 0 length key which indicates that this is the separator. The separator has no value.
+static constexpr uint8_t PSBT_SEPARATOR = 0x00;
+
+// Takes a stream and multiple arguments and serializes them into a vector and then into the stream
+// The resulting output into the stream has the total serialized length of all of the objects followed by all objects concatenated with each other.
+template<typename Stream, typename... X>
+void SerializeToVector(Stream& s, const X&... args)
+{
+    std::vector<unsigned char> ret;
+    CVectorWriter ss(SER_NETWORK, PROTOCOL_VERSION, ret, 0);
+    SerializeMany(ss, args...);
+    s << ret;
+}
+
+// Takes a stream and multiple arguments and unserializes them first as a vector then each object individually in the order provided in the arguments
+template<typename Stream, typename... X>
+void UnserializeFromVector(Stream& s, X&... args)
+{
+    std::vector<unsigned char> data;
+    s >> data;
+    CDataStream ss(data, SER_NETWORK, PROTOCOL_VERSION);
+    UnserializeMany(ss, args...);
+    if (!ss.eof()) {
+        throw std::ios_base::failure("Size of value was not the stated size");
+    }
+}
+
+// Deserialize HD keypaths into a map
+template<typename Stream>
+void DeserializeHDKeypaths(Stream& s, const std::vector<unsigned char>& key, std::map<CPubKey, std::vector<uint32_t>>& hd_keypaths)
+{
+    // Make sure that the key is the size of pubkey + 1
+    if (key.size() != CPubKey::PUBLIC_KEY_SIZE + 1 && key.size() != CPubKey::COMPRESSED_PUBLIC_KEY_SIZE + 1) {
+        throw std::ios_base::failure("Size of key was not the expected size for the type BIP32 keypath");
+    }
+    // Read in the pubkey from key
+    CPubKey pubkey(key.begin() + 1, key.end());
+    if (!pubkey.IsFullyValid()) {
+       throw std::ios_base::failure("Invalid pubkey");
+    }
+    if (hd_keypaths.count(pubkey) > 0) {
+        throw std::ios_base::failure("Duplicate Key, pubkey derivation path already provided");
+    }
+
+    // Read in key path
+    uint64_t value_len = ReadCompactSize(s);
+    std::vector<uint32_t> keypath;
+    for (unsigned int i = 0; i < value_len; i += sizeof(uint32_t)) {
+        uint32_t index;
+        s >> index;
+        keypath.push_back(index);
+    }
+
+    // Add to map
+    hd_keypaths.emplace(pubkey, keypath);
+}
+
+// Serialize HD keypaths to a stream from a map
+template<typename Stream>
+void SerializeHDKeypaths(Stream& s, const std::map<CPubKey, std::vector<uint32_t>>& hd_keypaths, uint8_t type)
+{
+    for (auto keypath_pair : hd_keypaths) {
+        SerializeToVector(s, type, MakeSpan(keypath_pair.first));
+        WriteCompactSize(s, keypath_pair.second.size() * sizeof(uint32_t));
+        for (auto& path : keypath_pair.second) {
+            s << path;
+        }
+    }
+}
+
+/** A structure for PSBTs which contain per-input information */
+struct PSBTInput
+{
+    CTransactionRef non_witness_utxo;
+    CTxOut witness_utxo;
+    CScript redeem_script;
+    CScript witness_script;
+    CScript final_script_sig;
+    CScriptWitness final_script_witness;
+    std::map<CPubKey, std::vector<uint32_t>> hd_keypaths;
+    std::map<CKeyID, SigPair> partial_sigs;
+    std::map<std::vector<unsigned char>, std::vector<unsigned char>> unknown;
+    int sighash_type = 0;
+
+    bool IsNull() const;
+    void FillSignatureData(SignatureData& sigdata) const;
+    void FromSignatureData(const SignatureData& sigdata);
+    void Merge(const PSBTInput& input);
+    bool IsSane() const;
+    PSBTInput() {}
+
+    template <typename Stream>
+    inline void Serialize(Stream& s) const {
+        // Write the utxo
+        // If there is a non-witness utxo, then don't add the witness one.
+        if (non_witness_utxo) {
+            SerializeToVector(s, PSBT_IN_NON_WITNESS_UTXO);
+            SerializeToVector(s, non_witness_utxo);
+        } else if (!witness_utxo.IsNull()) {
+            SerializeToVector(s, PSBT_IN_WITNESS_UTXO);
+            SerializeToVector(s, witness_utxo);
+        }
+
+        if (final_script_sig.empty() && final_script_witness.IsNull()) {
+            // Write any partial signatures
+            for (auto sig_pair : partial_sigs) {
+                SerializeToVector(s, PSBT_IN_PARTIAL_SIG, MakeSpan(sig_pair.second.first));
+                s << sig_pair.second.second;
+            }
+
+            // Write the sighash type
+            if (sighash_type > 0) {
+                SerializeToVector(s, PSBT_IN_SIGHASH);
+                SerializeToVector(s, sighash_type);
+            }
+
+            // Write the redeem script
+            if (!redeem_script.empty()) {
+                SerializeToVector(s, PSBT_IN_REDEEMSCRIPT);
+                s << redeem_script;
+            }
+
+            // Write the witness script
+            if (!witness_script.empty()) {
+                SerializeToVector(s, PSBT_IN_WITNESSSCRIPT);
+                s << witness_script;
+            }
+
+            // Write any hd keypaths
+            SerializeHDKeypaths(s, hd_keypaths, PSBT_IN_BIP32_DERIVATION);
+        }
+
+        // Write script sig
+        if (!final_script_sig.empty()) {
+            SerializeToVector(s, PSBT_IN_SCRIPTSIG);
+            s << final_script_sig;
+        }
+        // write script witness
+        if (!final_script_witness.IsNull()) {
+            SerializeToVector(s, PSBT_IN_SCRIPTWITNESS);
+            SerializeToVector(s, final_script_witness.stack);
+        }
+
+        // Write unknown things
+        for (auto& entry : unknown) {
+            s << entry.first;
+            s << entry.second;
+        }
+
+        s << PSBT_SEPARATOR;
+    }
+
+
+    template <typename Stream>
+    inline void Unserialize(Stream& s) {
+        // Read loop
+        while(!s.empty()) {
+            // Read
+            std::vector<unsigned char> key;
+            s >> key;
+
+            // the key is empty if that was actually a separator byte
+            // This is a special case for key lengths 0 as those are not allowed (except for separator)
+            if (key.empty()) return;
+
+            // First byte of key is the type
+            unsigned char type = key[0];
+
+            // Do stuff based on type
+            switch(type) {
+                case PSBT_IN_NON_WITNESS_UTXO:
+                    if (non_witness_utxo) {
+                        throw std::ios_base::failure("Duplicate Key, input non-witness utxo already provided");
+                    }
+                    UnserializeFromVector(s, non_witness_utxo);
+                    break;
+                case PSBT_IN_WITNESS_UTXO:
+                    if (!witness_utxo.IsNull()) {
+                        throw std::ios_base::failure("Duplicate Key, input witness utxo already provided");
+                    }
+                    UnserializeFromVector(s, witness_utxo);
+                    break;
+                case PSBT_IN_PARTIAL_SIG:
+                {
+                    // Make sure that the key is the size of pubkey + 1
+                    if (key.size() != CPubKey::PUBLIC_KEY_SIZE + 1 && key.size() != CPubKey::COMPRESSED_PUBLIC_KEY_SIZE + 1) {
+                        throw std::ios_base::failure("Size of key was not the expected size for the type partial signature pubkey");
+                    }
+                    // Read in the pubkey from key
+                    CPubKey pubkey(key.begin() + 1, key.end());
+                    if (!pubkey.IsFullyValid()) {
+                       throw std::ios_base::failure("Invalid pubkey");
+                    }
+                    if (partial_sigs.count(pubkey.GetID()) > 0) {
+                        throw std::ios_base::failure("Duplicate Key, input partial signature for pubkey already provided");
+                    }
+
+                    // Read in the signature from value
+                    std::vector<unsigned char> sig;
+                    s >> sig;
+
+                    // Add to list
+                    partial_sigs.emplace(pubkey.GetID(), SigPair(pubkey, std::move(sig)));
+                    break;
+                }
+                case PSBT_IN_SIGHASH:
+                    if (sighash_type > 0) {
+                        throw std::ios_base::failure("Duplicate Key, input sighash type already provided");
+                    }
+                    UnserializeFromVector(s, sighash_type);
+                    break;
+                case PSBT_IN_REDEEMSCRIPT:
+                {
+                    if (!redeem_script.empty()) {
+                        throw std::ios_base::failure("Duplicate Key, input redeemScript already provided");
+                    }
+                    s >> redeem_script;
+                    break;
+                }
+                case PSBT_IN_WITNESSSCRIPT:
+                {
+                    if (!witness_script.empty()) {
+                        throw std::ios_base::failure("Duplicate Key, input witnessScript already provided");
+                    }
+                    s >> witness_script;
+                    break;
+                }
+                case PSBT_IN_BIP32_DERIVATION:
+                {
+                    DeserializeHDKeypaths(s, key, hd_keypaths);
+                    break;
+                }
+                case PSBT_IN_SCRIPTSIG:
+                {
+                    if (!final_script_sig.empty()) {
+                        throw std::ios_base::failure("Duplicate Key, input final scriptSig already provided");
+                    }
+                    s >> final_script_sig;
+                    break;
+                }
+                case PSBT_IN_SCRIPTWITNESS:
+                {
+                    if (!final_script_witness.IsNull()) {
+                        throw std::ios_base::failure("Duplicate Key, input final scriptWitness already provided");
+                    }
+                    UnserializeFromVector(s, final_script_witness.stack);
+                    break;
+                }
+                // Unknown stuff
+                default:
+                    if (unknown.count(key) > 0) {
+                        throw std::ios_base::failure("Duplicate Key, key for unknown value already provided");
+                    }
+                    // Read in the value
+                    std::vector<unsigned char> val_bytes;
+                    s >> val_bytes;
+                    unknown.emplace(std::move(key), std::move(val_bytes));
+                    break;
+            }
+        }
+    }
+
+    template <typename Stream>
+    PSBTInput(deserialize_type, Stream& s) {
+        Unserialize(s);
+    }
+};
+
+/** A structure for PSBTs which contains per output information */
+struct PSBTOutput
+{
+    CScript redeem_script;
+    CScript witness_script;
+    std::map<CPubKey, std::vector<uint32_t>> hd_keypaths;
+    std::map<std::vector<unsigned char>, std::vector<unsigned char>> unknown;
+
+    bool IsNull() const;
+    void FillSignatureData(SignatureData& sigdata) const;
+    void FromSignatureData(const SignatureData& sigdata);
+    void Merge(const PSBTOutput& output);
+    bool IsSane() const;
+    PSBTOutput() {}
+
+    template <typename Stream>
+    inline void Serialize(Stream& s) const {
+        // Write the redeem script
+        if (!redeem_script.empty()) {
+            SerializeToVector(s, PSBT_OUT_REDEEMSCRIPT);
+            s << redeem_script;
+        }
+
+        // Write the witness script
+        if (!witness_script.empty()) {
+            SerializeToVector(s, PSBT_OUT_WITNESSSCRIPT);
+            s << witness_script;
+        }
+
+        // Write any hd keypaths
+        SerializeHDKeypaths(s, hd_keypaths, PSBT_OUT_BIP32_DERIVATION);
+
+        // Write unknown things
+        for (auto& entry : unknown) {
+            s << entry.first;
+            s << entry.second;
+        }
+
+        s << PSBT_SEPARATOR;
+    }
+
+
+    template <typename Stream>
+    inline void Unserialize(Stream& s) {
+        // Read loop
+        while(!s.empty()) {
+            // Read
+            std::vector<unsigned char> key;
+            s >> key;
+
+            // the key is empty if that was actually a separator byte
+            // This is a special case for key lengths 0 as those are not allowed (except for separator)
+            if (key.empty()) return;
+
+            // First byte of key is the type
+            unsigned char type = key[0];
+
+            // Do stuff based on type
+            switch(type) {
+                case PSBT_OUT_REDEEMSCRIPT:
+                {
+                    if (!redeem_script.empty()) {
+                        throw std::ios_base::failure("Duplicate Key, output redeemScript already provided");
+                    }
+                    s >> redeem_script;
+                    break;
+                }
+                case PSBT_OUT_WITNESSSCRIPT:
+                {
+                    if (!witness_script.empty()) {
+                        throw std::ios_base::failure("Duplicate Key, output witnessScript already provided");
+                    }
+                    s >> witness_script;
+                    break;
+                }
+                case PSBT_OUT_BIP32_DERIVATION:
+                {
+                    DeserializeHDKeypaths(s, key, hd_keypaths);
+                    break;
+                }
+                // Unknown stuff
+                default: {
+                    if (unknown.count(key) > 0) {
+                        throw std::ios_base::failure("Duplicate Key, key for unknown value already provided");
+                    }
+                    // Read in the value
+                    std::vector<unsigned char> val_bytes;
+                    s >> val_bytes;
+                    unknown.emplace(std::move(key), std::move(val_bytes));
+                    break;
+                }
+            }
+        }
+    }
+
+    template <typename Stream>
+    PSBTOutput(deserialize_type, Stream& s) {
+        Unserialize(s);
+    }
+};
+
+/** A version of CTransaction with the PSBT format*/
+struct PartiallySignedTransaction
+{
+    boost::optional<CMutableTransaction> tx;
+    std::vector<PSBTInput> inputs;
+    std::vector<PSBTOutput> outputs;
+    std::map<std::vector<unsigned char>, std::vector<unsigned char>> unknown;
+
+    bool IsNull() const;
+    void Merge(const PartiallySignedTransaction& psbt);
+    bool IsSane() const;
+    PartiallySignedTransaction() {}
+    PartiallySignedTransaction(const PartiallySignedTransaction& psbt_in) : tx(psbt_in.tx), inputs(psbt_in.inputs), outputs(psbt_in.outputs), unknown(psbt_in.unknown) {}
+
+    // Only checks if they refer to the same transaction
+    friend bool operator==(const PartiallySignedTransaction& a, const PartiallySignedTransaction &b)
+    {
+        return a.tx->GetHash() == b.tx->GetHash();
+    }
+    friend bool operator!=(const PartiallySignedTransaction& a, const PartiallySignedTransaction &b)
+    {
+        return !(a == b);
+    }
+
+    template <typename Stream>
+    inline void Serialize(Stream& s) const {
+
+        // magic bytes
+        s << PSBT_MAGIC_BYTES;
+
+        // unsigned tx flag
+        SerializeToVector(s, PSBT_GLOBAL_UNSIGNED_TX);
+
+        // Write serialized tx to a stream
+        SerializeToVector(s, *tx);
+
+        // Write the unknown things
+        for (auto& entry : unknown) {
+            s << entry.first;
+            s << entry.second;
+        }
+
+        // Separator
+        s << PSBT_SEPARATOR;
+
+        // Write inputs
+        for (const PSBTInput& input : inputs) {
+            s << input;
+        }
+        // Write outputs
+        for (const PSBTOutput& output : outputs) {
+            s << output;
+        }
+    }
+
+
+    template <typename Stream>
+    inline void Unserialize(Stream& s) {
+        // Read the magic bytes
+        uint8_t magic[5];
+        s >> magic;
+        if (!std::equal(magic, magic + 5, PSBT_MAGIC_BYTES)) {
+            throw std::ios_base::failure("Invalid PSBT magic bytes");
+        }
+
+        // Read global data
+        while(!s.empty()) {
+            // Read
+            std::vector<unsigned char> key;
+            s >> key;
+
+            // the key is empty if that was actually a separator byte
+            // This is a special case for key lengths 0 as those are not allowed (except for separator)
+            if (key.empty()) break;
+
+            // First byte of key is the type
+            unsigned char type = key[0];
+
+            // Do stuff based on type
+            switch(type) {
+                case PSBT_GLOBAL_UNSIGNED_TX:
+                {
+                    if (tx) {
+                        throw std::ios_base::failure("Duplicate Key, unsigned tx already provided");
+                    }
+                    CMutableTransaction mtx;
+                    UnserializeFromVector(s, mtx);
+                    tx = std::move(mtx);
+                    // Make sure that all scriptSigs and scriptWitnesses are empty
+                    for (const CTxIn& txin : tx->vin) {
+                        if (!txin.scriptSig.empty() || !txin.scriptWitness.IsNull()) {
+                            throw std::ios_base::failure("Unsigned tx does not have empty scriptSigs and scriptWitnesses.");
+                        }
+                    }
+                    break;
+                }
+                // Unknown stuff
+                default: {
+                    if (unknown.count(key) > 0) {
+                        throw std::ios_base::failure("Duplicate Key, key for unknown value already provided");
+                    }
+                    // Read in the value
+                    std::vector<unsigned char> val_bytes;
+                    s >> val_bytes;
+                    unknown.emplace(std::move(key), std::move(val_bytes));
+                }
+            }
+        }
+
+        // Make sure that we got an unsigned tx
+        if (!tx) {
+            throw std::ios_base::failure("No unsigned transcation was provided");
+        }
+
+        // Read input data
+        unsigned int i = 0;
+        while (!s.empty() && i < tx->vin.size()) {
+            PSBTInput input;
+            s >> input;
+            inputs.push_back(input);
+
+            // Make sure the non-witness utxo matches the outpoint
+            if (input.non_witness_utxo && input.non_witness_utxo->GetHash() != tx->vin[i].prevout.hash) {
+                throw std::ios_base::failure("Non-witness UTXO does not match outpoint hash");
+            }
+            ++i;
+        }
+        // Make sure that the number of inputs matches the number of inputs in the transaction
+        if (inputs.size() != tx->vin.size()) {
+            throw std::ios_base::failure("Inputs provided does not match the number of inputs in transaction.");
+        }
+
+        // Read output data
+        i = 0;
+        while (!s.empty() && i < tx->vout.size()) {
+            PSBTOutput output;
+            s >> output;
+            outputs.push_back(output);
+            ++i;
+        }
+        // Make sure that the number of outputs matches the number of outputs in the transaction
+        if (outputs.size() != tx->vout.size()) {
+            throw std::ios_base::failure("Outputs provided does not match the number of outputs in transaction.");
+        }
+        // Sanity check
+        if (!IsSane()) {
+            throw std::ios_base::failure("PSBT is not sane.");
+        }
+    }
+
+    template <typename Stream>
+    PartiallySignedTransaction(deserialize_type, Stream& s) {
+        Unserialize(s);
+    }
+};
+
 /** Produce a script signature using a generic signature creator. */
 bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreator& creator, const CScript& scriptPubKey, SignatureData& sigdata);
 
@@ -80,6 +645,9 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
 bool SignSignature(const SigningProvider &provider, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType);
 bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType);
 
+/** Signs a PSBTInput */
+bool SignPSBTInput(const SigningProvider& provider, const CMutableTransaction& tx, PSBTInput& input, SignatureData& sigdata, int index, int sighash = 1);
+
 /** Extract signature data from a transaction input, and insert it. */
 SignatureData DataFromTransaction(const CMutableTransaction& tx, unsigned int nIn, const CTxOut& txout);
 void UpdateInput(CTxIn& input, const SignatureData& data);