Merge #13425: Moving final scriptSig construction from CombineSignatures to ProduceSignature (PSBT signer logic)

b81560029 Remove CombineSignatures and replace tests (Andrew Chow)
ed94c8b55 Replace CombineSignatures with ProduceSignature (Andrew Chow)
0422beb9b Make SignatureData able to store signatures and scripts (Andrew Chow)
b6edb4f5e Inline Sign1 and SignN (Andrew Chow)

Pull request description:

  Currently CombineSignatures is used to create the final scriptSig or an input. However ProduceSignature is capable of doing this itself. Using both CombineSignatures and ProduceSignature results in code duplication which is unnecessary.

  To move the scriptSig construction to ProduceSignatures, the SignatureData class contains two maps to hold pubkeys mapped to signatures, and script ids mapped to scripts. DataFromTransaction is extended to be able to extract signatures, their public keys, and scripts from existing ScriptSigs.

  The SignaureData are then passed down to SignStep which can use the aforementioned maps to get the signatures, pubkeys, and scripts that it needs, falling back to the actual SigningProvider and SignatureCreator if the data are not available in the SignatureData.

  Additionally, Sign1 and SignN have been removed and their functionality inlined into SignStep since Sign1 is really just a wrapper around CreateSig.

  Since ProduceSignature can produce the final scriptSig or scriptWitness by using SignatureData which has extracted data from the transaction, CombineSignatures is unnecessary as ProduceSignature is able to replicate all of CombineSignatures' functionality.

  This also furthers BIP 174 support and begins moving towards a BIP 174 style backend.

  The tests have also been updated to use the new combining methodology.

Tree-SHA512: 78cd58a4ebe37f79229bd5eee2958a0bb45cd7f36d0e993eee13ff685b3665dd76ef2dfd5f47d34678995bb587f5594100ee5f6c09b1c69ee96d3684d470d01e

2 files changed, 215 insertions, 211 deletions

diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index 6dbfbda029..60a8a2655d 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -33,27 +33,51 @@ bool MutableTransactionSignatureCreator::CreateSig(const SigningProvider& provid
     return true;
 }
 
-static bool Sign1(const SigningProvider& provider, const CKeyID& address, const BaseSignatureCreator& creator, const CScript& scriptCode, std::vector<valtype>& ret, SigVersion sigversion)
+static bool GetCScript(const SigningProvider& provider, const SignatureData& sigdata, const CScriptID& scriptid, CScript& script)
 {
-    std::vector<unsigned char> vchSig;
-    if (!creator.CreateSig(provider, vchSig, address, scriptCode, sigversion))
-        return false;
-    ret.push_back(vchSig);
-    return true;
+    if (provider.GetCScript(scriptid, script)) {
+        return true;
+    }
+    // Look for scripts in SignatureData
+    if (CScriptID(sigdata.redeem_script) == scriptid) {
+        script = sigdata.redeem_script;
+        return true;
+    } else if (CScriptID(sigdata.witness_script) == scriptid) {
+        script = sigdata.witness_script;
+        return true;
+    }
+    return false;
 }
 
-static bool SignN(const SigningProvider& provider, const std::vector<valtype>& multisigdata, const BaseSignatureCreator& creator, const CScript& scriptCode, std::vector<valtype>& ret, SigVersion sigversion)
+static bool GetPubKey(const SigningProvider& provider, const SignatureData& sigdata, const CKeyID& address, CPubKey& pubkey)
 {
-    int nSigned = 0;
-    int nRequired = multisigdata.front()[0];
-    for (unsigned int i = 1; i < multisigdata.size()-1 && nSigned < nRequired; i++)
-    {
-        const valtype& pubkey = multisigdata[i];
-        CKeyID keyID = CPubKey(pubkey).GetID();
-        if (Sign1(provider, keyID, creator, scriptCode, ret, sigversion))
-            ++nSigned;
+    if (provider.GetPubKey(address, pubkey)) {
+        return true;
+    }
+    // Look for pubkey in all partial sigs
+    const auto it = sigdata.signatures.find(address);
+    if (it != sigdata.signatures.end()) {
+        pubkey = it->second.first;
+        return true;
     }
-    return nSigned==nRequired;
+    return false;
+}
+
+static bool CreateSig(const BaseSignatureCreator& creator, SignatureData& sigdata, const SigningProvider& provider, std::vector<unsigned char>& sig_out, const CKeyID& keyid, const CScript& scriptcode, SigVersion sigversion)
+{
+    const auto it = sigdata.signatures.find(keyid);
+    if (it != sigdata.signatures.end()) {
+        sig_out = it->second.second;
+        return true;
+    }
+    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;
+    }
+    return false;
 }
 
 /**
@@ -63,17 +87,17 @@ static bool SignN(const SigningProvider& provider, const std::vector<valtype>& m
  * Returns false if scriptPubKey could not be completely satisfied.
  */
 static bool SignStep(const SigningProvider& provider, const BaseSignatureCreator& creator, const CScript& scriptPubKey,
-                     std::vector<valtype>& ret, txnouttype& whichTypeRet, SigVersion sigversion)
+                     std::vector<valtype>& ret, txnouttype& whichTypeRet, SigVersion sigversion, SignatureData& sigdata)
 {
     CScript scriptRet;
     uint160 h160;
     ret.clear();
+    std::vector<unsigned char> sig;
 
     std::vector<valtype> vSolutions;
     if (!Solver(scriptPubKey, whichTypeRet, vSolutions))
         return false;
 
-    CKeyID keyID;
     switch (whichTypeRet)
     {
     case TX_NONSTANDARD:
@@ -81,37 +105,47 @@ static bool SignStep(const SigningProvider& provider, const BaseSignatureCreator
     case TX_WITNESS_UNKNOWN:
         return false;
     case TX_PUBKEY:
-        keyID = CPubKey(vSolutions[0]).GetID();
-        return Sign1(provider, keyID, creator, scriptPubKey, ret, sigversion);
-    case TX_PUBKEYHASH:
-        keyID = CKeyID(uint160(vSolutions[0]));
-        if (!Sign1(provider, keyID, creator, scriptPubKey, ret, sigversion))
-            return false;
-        else
-        {
-            CPubKey vch;
-            provider.GetPubKey(keyID, vch);
-            ret.push_back(ToByteVector(vch));
-        }
+        if (!CreateSig(creator, sigdata, provider, sig, CPubKey(vSolutions[0]).GetID(), scriptPubKey, sigversion)) return false;
+        ret.push_back(std::move(sig));
+        return true;
+    case TX_PUBKEYHASH: {
+        CKeyID keyID = CKeyID(uint160(vSolutions[0]));
+        if (!CreateSig(creator, sigdata, provider, sig, keyID, scriptPubKey, sigversion)) return false;
+        ret.push_back(std::move(sig));
+        CPubKey pubkey;
+        GetPubKey(provider, sigdata, keyID, pubkey);
+        ret.push_back(ToByteVector(pubkey));
         return true;
+    }
     case TX_SCRIPTHASH:
-        if (provider.GetCScript(uint160(vSolutions[0]), scriptRet)) {
+        if (GetCScript(provider, sigdata, uint160(vSolutions[0]), scriptRet)) {
             ret.push_back(std::vector<unsigned char>(scriptRet.begin(), scriptRet.end()));
             return true;
         }
         return false;
 
-    case TX_MULTISIG:
+    case TX_MULTISIG: {
+        size_t required = vSolutions.front()[0];
         ret.push_back(valtype()); // workaround CHECKMULTISIG bug
-        return (SignN(provider, vSolutions, creator, scriptPubKey, ret, sigversion));
-
+        for (size_t i = 1; i < vSolutions.size() - 1; ++i) {
+            CPubKey pubkey = CPubKey(vSolutions[i]);
+            if (ret.size() < required + 1 && CreateSig(creator, sigdata, provider, sig, pubkey.GetID(), scriptPubKey, sigversion)) {
+                ret.push_back(std::move(sig));
+            }
+        }
+        bool ok = ret.size() == required + 1;
+        for (size_t i = 0; i + ret.size() < required + 1; ++i) {
+            ret.push_back(valtype());
+        }
+        return ok;
+    }
     case TX_WITNESS_V0_KEYHASH:
         ret.push_back(vSolutions[0]);
         return true;
 
     case TX_WITNESS_V0_SCRIPTHASH:
         CRIPEMD160().Write(&vSolutions[0][0], vSolutions[0].size()).Finalize(h160.begin());
-        if (provider.GetCScript(h160, scriptRet)) {
+        if (GetCScript(provider, sigdata, h160, scriptRet)) {
             ret.push_back(std::vector<unsigned char>(scriptRet.begin(), scriptRet.end()));
             return true;
         }
@@ -139,9 +173,11 @@ static CScript PushAll(const std::vector<valtype>& values)
 
 bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreator& creator, const CScript& fromPubKey, SignatureData& sigdata)
 {
+    if (sigdata.complete) return true;
+
     std::vector<valtype> result;
     txnouttype whichType;
-    bool solved = SignStep(provider, creator, fromPubKey, result, whichType, SigVersion::BASE);
+    bool solved = SignStep(provider, creator, fromPubKey, result, whichType, SigVersion::BASE, sigdata);
     bool P2SH = false;
     CScript subscript;
     sigdata.scriptWitness.stack.clear();
@@ -152,7 +188,8 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
         // the final scriptSig is the signatures from that
         // and then the serialized subscript:
         subscript = CScript(result[0].begin(), result[0].end());
-        solved = solved && SignStep(provider, creator, subscript, result, whichType, SigVersion::BASE) && whichType != TX_SCRIPTHASH;
+        sigdata.redeem_script = subscript;
+        solved = solved && SignStep(provider, creator, subscript, result, whichType, SigVersion::BASE, sigdata) && whichType != TX_SCRIPTHASH;
         P2SH = true;
     }
 
@@ -161,15 +198,16 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
         CScript witnessscript;
         witnessscript << OP_DUP << OP_HASH160 << ToByteVector(result[0]) << OP_EQUALVERIFY << OP_CHECKSIG;
         txnouttype subType;
-        solved = solved && SignStep(provider, creator, witnessscript, result, subType, SigVersion::WITNESS_V0);
+        solved = solved && SignStep(provider, creator, witnessscript, result, subType, SigVersion::WITNESS_V0, sigdata);
         sigdata.scriptWitness.stack = result;
         result.clear();
     }
     else if (solved && whichType == TX_WITNESS_V0_SCRIPTHASH)
     {
         CScript witnessscript(result[0].begin(), result[0].end());
+        sigdata.witness_script = witnessscript;
         txnouttype subType;
-        solved = solved && SignStep(provider, creator, witnessscript, result, subType, SigVersion::WITNESS_V0) && subType != TX_SCRIPTHASH && subType != TX_WITNESS_V0_SCRIPTHASH && subType != TX_WITNESS_V0_KEYHASH;
+        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;
         result.clear();
@@ -181,99 +219,29 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
     sigdata.scriptSig = PushAll(result);
 
     // Test solution
-    return solved && VerifyScript(sigdata.scriptSig, fromPubKey, &sigdata.scriptWitness, STANDARD_SCRIPT_VERIFY_FLAGS, creator.Checker());
-}
-
-SignatureData DataFromTransaction(const CMutableTransaction& tx, unsigned int nIn)
-{
-    SignatureData data;
-    assert(tx.vin.size() > nIn);
-    data.scriptSig = tx.vin[nIn].scriptSig;
-    data.scriptWitness = tx.vin[nIn].scriptWitness;
-    return data;
+    sigdata.complete = solved && VerifyScript(sigdata.scriptSig, fromPubKey, &sigdata.scriptWitness, STANDARD_SCRIPT_VERIFY_FLAGS, creator.Checker());
+    return sigdata.complete;
 }
 
-void UpdateInput(CTxIn& input, const SignatureData& data)
+class SignatureExtractorChecker final : public BaseSignatureChecker
 {
-    input.scriptSig = data.scriptSig;
-    input.scriptWitness = data.scriptWitness;
-}
+private:
+    SignatureData& sigdata;
+    BaseSignatureChecker& checker;
 
-bool SignSignature(const SigningProvider &provider, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType)
-{
-    assert(nIn < txTo.vin.size());
-
-    MutableTransactionSignatureCreator creator(&txTo, nIn, amount, nHashType);
-
-    SignatureData sigdata;
-    bool ret = ProduceSignature(provider, creator, fromPubKey, sigdata);
-    UpdateInput(txTo.vin.at(nIn), sigdata);
-    return ret;
-}
-
-bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType)
-{
-    assert(nIn < txTo.vin.size());
-    CTxIn& txin = txTo.vin[nIn];
-    assert(txin.prevout.n < txFrom.vout.size());
-    const CTxOut& txout = txFrom.vout[txin.prevout.n];
-
-    return SignSignature(provider, txout.scriptPubKey, txTo, nIn, txout.nValue, nHashType);
-}
+public:
+    SignatureExtractorChecker(SignatureData& sigdata, BaseSignatureChecker& checker) : sigdata(sigdata), checker(checker) {}
+    bool CheckSig(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override;
+};
 
-static std::vector<valtype> CombineMultisig(const CScript& scriptPubKey, const BaseSignatureChecker& checker,
-                               const std::vector<valtype>& vSolutions,
-                               const std::vector<valtype>& sigs1, const std::vector<valtype>& sigs2, SigVersion sigversion)
+bool SignatureExtractorChecker::CheckSig(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const
 {
-    // Combine all the signatures we've got:
-    std::set<valtype> allsigs;
-    for (const valtype& v : sigs1)
-    {
-        if (!v.empty())
-            allsigs.insert(v);
-    }
-    for (const valtype& v : sigs2)
-    {
-        if (!v.empty())
-            allsigs.insert(v);
-    }
-
-    // Build a map of pubkey -> signature by matching sigs to pubkeys:
-    assert(vSolutions.size() > 1);
-    unsigned int nSigsRequired = vSolutions.front()[0];
-    unsigned int nPubKeys = vSolutions.size()-2;
-    std::map<valtype, valtype> sigs;
-    for (const valtype& sig : allsigs)
-    {
-        for (unsigned int i = 0; i < nPubKeys; i++)
-        {
-            const valtype& pubkey = vSolutions[i+1];
-            if (sigs.count(pubkey))
-                continue; // Already got a sig for this pubkey
-
-            if (checker.CheckSig(sig, pubkey, scriptPubKey, sigversion))
-            {
-                sigs[pubkey] = sig;
-                break;
-            }
-        }
-    }
-    // Now build a merged CScript:
-    unsigned int nSigsHave = 0;
-    std::vector<valtype> result; result.push_back(valtype()); // pop-one-too-many workaround
-    for (unsigned int i = 0; i < nPubKeys && nSigsHave < nSigsRequired; i++)
-    {
-        if (sigs.count(vSolutions[i+1]))
-        {
-            result.push_back(sigs[vSolutions[i+1]]);
-            ++nSigsHave;
-        }
+    if (checker.CheckSig(scriptSig, vchPubKey, scriptCode, sigversion)) {
+        CPubKey pubkey(vchPubKey);
+        sigdata.signatures.emplace(pubkey.GetID(), SigPair(pubkey, scriptSig));
+        return true;
     }
-    // Fill any missing with OP_0:
-    for (unsigned int i = nSigsHave; i < nSigsRequired; i++)
-        result.push_back(valtype());
-
-    return result;
+    return false;
 }
 
 namespace
@@ -298,89 +266,115 @@ struct Stacks
 };
 }
 
-static Stacks CombineSignatures(const CScript& scriptPubKey, const BaseSignatureChecker& checker,
-                                 const txnouttype txType, const std::vector<valtype>& vSolutions,
-                                 Stacks sigs1, Stacks sigs2, SigVersion sigversion)
+// Extracts signatures and scripts from incomplete scriptSigs. Please do not extend this, use PSBT instead
+SignatureData DataFromTransaction(const CMutableTransaction& tx, unsigned int nIn, const CTxOut& txout)
 {
-    switch (txType)
-    {
-    case TX_NONSTANDARD:
-    case TX_NULL_DATA:
-    case TX_WITNESS_UNKNOWN:
-        // Don't know anything about this, assume bigger one is correct:
-        if (sigs1.script.size() >= sigs2.script.size())
-            return sigs1;
-        return sigs2;
-    case TX_PUBKEY:
-    case TX_PUBKEYHASH:
-        // Signatures are bigger than placeholders or empty scripts:
-        if (sigs1.script.empty() || sigs1.script[0].empty())
-            return sigs2;
-        return sigs1;
-    case TX_WITNESS_V0_KEYHASH:
-        // Signatures are bigger than placeholders or empty scripts:
-        if (sigs1.witness.empty() || sigs1.witness[0].empty())
-            return sigs2;
-        return sigs1;
-    case TX_SCRIPTHASH:
-        if (sigs1.script.empty() || sigs1.script.back().empty())
-            return sigs2;
-        else if (sigs2.script.empty() || sigs2.script.back().empty())
-            return sigs1;
-        else
-        {
-            // Recur to combine:
-            valtype spk = sigs1.script.back();
-            CScript pubKey2(spk.begin(), spk.end());
-
-            txnouttype txType2;
-            std::vector<std::vector<unsigned char> > vSolutions2;
-            Solver(pubKey2, txType2, vSolutions2);
-            sigs1.script.pop_back();
-            sigs2.script.pop_back();
-            Stacks result = CombineSignatures(pubKey2, checker, txType2, vSolutions2, sigs1, sigs2, sigversion);
-            result.script.push_back(spk);
-            return result;
-        }
-    case TX_MULTISIG:
-        return Stacks(CombineMultisig(scriptPubKey, checker, vSolutions, sigs1.script, sigs2.script, sigversion));
-    case TX_WITNESS_V0_SCRIPTHASH:
-        if (sigs1.witness.empty() || sigs1.witness.back().empty())
-            return sigs2;
-        else if (sigs2.witness.empty() || sigs2.witness.back().empty())
-            return sigs1;
-        else
-        {
-            // Recur to combine:
-            CScript pubKey2(sigs1.witness.back().begin(), sigs1.witness.back().end());
-            txnouttype txType2;
-            std::vector<valtype> vSolutions2;
-            Solver(pubKey2, txType2, vSolutions2);
-            sigs1.witness.pop_back();
-            sigs1.script = sigs1.witness;
-            sigs1.witness.clear();
-            sigs2.witness.pop_back();
-            sigs2.script = sigs2.witness;
-            sigs2.witness.clear();
-            Stacks result = CombineSignatures(pubKey2, checker, txType2, vSolutions2, sigs1, sigs2, SigVersion::WITNESS_V0);
-            result.witness = result.script;
-            result.script.clear();
-            result.witness.push_back(valtype(pubKey2.begin(), pubKey2.end()));
-            return result;
+    SignatureData data;
+    assert(tx.vin.size() > nIn);
+    data.scriptSig = tx.vin[nIn].scriptSig;
+    data.scriptWitness = tx.vin[nIn].scriptWitness;
+    Stacks stack(data);
+
+    // Get signatures
+    MutableTransactionSignatureChecker tx_checker(&tx, nIn, txout.nValue);
+    SignatureExtractorChecker extractor_checker(data, tx_checker);
+    if (VerifyScript(data.scriptSig, txout.scriptPubKey, &data.scriptWitness, STANDARD_SCRIPT_VERIFY_FLAGS, extractor_checker)) {
+        data.complete = true;
+        return data;
+    }
+
+    // Get scripts
+    txnouttype script_type;
+    std::vector<std::vector<unsigned char>> solutions;
+    Solver(txout.scriptPubKey, script_type, solutions);
+    SigVersion sigversion = SigVersion::BASE;
+    CScript next_script = txout.scriptPubKey;
+
+    if (script_type == TX_SCRIPTHASH && !stack.script.empty() && !stack.script.back().empty()) {
+        // Get the redeemScript
+        CScript redeem_script(stack.script.back().begin(), stack.script.back().end());
+        data.redeem_script = redeem_script;
+        next_script = std::move(redeem_script);
+
+        // Get redeemScript type
+        Solver(next_script, script_type, solutions);
+        stack.script.pop_back();
+    }
+    if (script_type == TX_WITNESS_V0_SCRIPTHASH && !stack.witness.empty() && !stack.witness.back().empty()) {
+        // Get the witnessScript
+        CScript witness_script(stack.witness.back().begin(), stack.witness.back().end());
+        data.witness_script = witness_script;
+        next_script = std::move(witness_script);
+
+        // Get witnessScript type
+        Solver(next_script, script_type, solutions);
+        stack.witness.pop_back();
+        stack.script = std::move(stack.witness);
+        stack.witness.clear();
+        sigversion = SigVersion::WITNESS_V0;
+    }
+    if (script_type == TX_MULTISIG && !stack.script.empty()) {
+        // Build a map of pubkey -> signature by matching sigs to pubkeys:
+        assert(solutions.size() > 1);
+        unsigned int num_pubkeys = solutions.size()-2;
+        unsigned int last_success_key = 0;
+        for (const valtype& sig : stack.script) {
+            for (unsigned int i = last_success_key; i < num_pubkeys; ++i) {
+                const valtype& pubkey = solutions[i+1];
+                // We either have a signature for this pubkey, or we have found a signature and it is valid
+                if (data.signatures.count(CPubKey(pubkey).GetID()) || extractor_checker.CheckSig(sig, pubkey, next_script, sigversion)) {
+                    last_success_key = i + 1;
+                    break;
+                }
+            }
         }
-    default:
-        return Stacks();
     }
+
+    return data;
+}
+
+void UpdateInput(CTxIn& input, const SignatureData& data)
+{
+    input.scriptSig = data.scriptSig;
+    input.scriptWitness = data.scriptWitness;
+}
+
+void SignatureData::MergeSignatureData(SignatureData sigdata)
+{
+    if (complete) return;
+    if (sigdata.complete) {
+        *this = std::move(sigdata);
+        return;
+    }
+    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;
+    }
+    signatures.insert(std::make_move_iterator(sigdata.signatures.begin()), std::make_move_iterator(sigdata.signatures.end()));
+}
+
+bool SignSignature(const SigningProvider &provider, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType)
+{
+    assert(nIn < txTo.vin.size());
+
+    MutableTransactionSignatureCreator creator(&txTo, nIn, amount, nHashType);
+
+    SignatureData sigdata;
+    bool ret = ProduceSignature(provider, creator, fromPubKey, sigdata);
+    UpdateInput(txTo.vin.at(nIn), sigdata);
+    return ret;
 }
 
-SignatureData CombineSignatures(const CScript& scriptPubKey, const BaseSignatureChecker& checker,
-                          const SignatureData& scriptSig1, const SignatureData& scriptSig2)
+bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType)
 {
-    txnouttype txType;
-    std::vector<std::vector<unsigned char> > vSolutions;
-    Solver(scriptPubKey, txType, vSolutions);
+    assert(nIn < txTo.vin.size());
+    CTxIn& txin = txTo.vin[nIn];
+    assert(txin.prevout.n < txFrom.vout.size());
+    const CTxOut& txout = txFrom.vout[txin.prevout.n];
 
-    return CombineSignatures(scriptPubKey, checker, txType, vSolutions, Stacks(scriptSig1), Stacks(scriptSig2), SigVersion::BASE).Output();
+    return SignSignature(provider, txout.scriptPubKey, txTo, nIn, txout.nValue, nHashType);
 }
 
 namespace {
@@ -416,6 +410,7 @@ public:
 }
 
 const BaseSignatureCreator& DUMMY_SIGNATURE_CREATOR = DummySignatureCreator();
+const SigningProvider& DUMMY_SIGNING_PROVIDER = SigningProvider();
 
 bool IsSolvable(const SigningProvider& provider, const CScript& script)
 {
diff --git a/src/script/sign.h b/src/script/sign.h
index 8ef0306bfe..3666859641 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -21,11 +21,13 @@ class SigningProvider
 {
 public:
     virtual ~SigningProvider() {}
-    virtual bool GetCScript(const CScriptID &scriptid, CScript& script) const =0;
-    virtual bool GetPubKey(const CKeyID &address, CPubKey& pubkey) const =0;
-    virtual bool GetKey(const CKeyID &address, CKey& key) const =0;
+    virtual bool GetCScript(const CScriptID &scriptid, CScript& script) const { return false; }
+    virtual bool GetPubKey(const CKeyID &address, CPubKey& pubkey) const { return false; }
+    virtual bool GetKey(const CKeyID &address, CKey& key) const { return false; }
 };
 
+extern const SigningProvider& DUMMY_SIGNING_PROVIDER;
+
 /** Interface for signature creators. */
 class BaseSignatureCreator {
 public:
@@ -53,12 +55,22 @@ public:
 /** A signature creator that just produces 72-byte empty signatures. */
 extern const BaseSignatureCreator& DUMMY_SIGNATURE_CREATOR;
 
+typedef std::pair<CPubKey, std::vector<unsigned char>> SigPair;
+
+// This struct contains information from a transaction input and also contains signatures for that input.
+// The information contained here can be used to create a signature and is also filled by ProduceSignature
+// in order to construct final scriptSigs and scriptWitnesses.
 struct SignatureData {
-    CScript scriptSig;
-    CScriptWitness scriptWitness;
+    bool complete = false; ///< Stores whether the scriptSig and scriptWitness are complete
+    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.
 
     SignatureData() {}
     explicit SignatureData(const CScript& script) : scriptSig(script) {}
+    void MergeSignatureData(SignatureData sigdata);
 };
 
 /** Produce a script signature using a generic signature creator. */
@@ -68,11 +80,8 @@ 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);
 
-/** Combine two script signatures using a generic signature checker, intelligently, possibly with OP_0 placeholders. */
-SignatureData CombineSignatures(const CScript& scriptPubKey, const BaseSignatureChecker& checker, const SignatureData& scriptSig1, const SignatureData& scriptSig2);
-
-/** Extract signature data from a transaction, and insert it. */
-SignatureData DataFromTransaction(const CMutableTransaction& tx, unsigned int nIn);
+/** 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);
 
 /* Check whether we know how to sign for an output like this, assuming we