Merge bitcoin/bitcoin#24149: Signing support for Miniscript Descriptors

6c7a17a8e0eec377f83ed1399f003ae70b898270 psbt: support externally provided preimages for Miniscript satisfaction (Antoine Poinsot)
840a396029316896beda46600aec3c1af09a899c qa: add a "smart" Miniscript fuzz target (Antoine Poinsot)
17e3547241d593bc92c5c6b36c54284d9d9f3feb qa: add a fuzz target generating random nodes from a binary encoding (Antoine Poinsot)
611e12502a5887ffb751bb92fadaa334d484824b qa: functional test Miniscript signing with key and timelocks (Antoine Poinsot)
d57b7f2021d2369f6e88cdf0f562aab27c51beaf refactor: make descriptors in Miniscript functional test more readable (Antoine Poinsot)
0a8fc9e200b5018c1efd6f9126eb405ca0beeea3 wallet: check solvability using descriptor in AvailableCoins (Antoine Poinsot)
560e62b1e221832ae99ff8684559a7b8f9df84a7 script/sign: signing support for Miniscripts with hash preimage challenges (Antoine Poinsot)
a2f81b6a8f1ff3b0750711409c7538812a52ef40 script/sign: signing support for Miniscript with timelocks (Antoine Poinsot)
61c6d1a8440db09c44d7fd367a6f2c641ea93d40 script/sign: basic signing support for Miniscript descriptors (Antoine Poinsot)
4242c1c52127df3a24be0c15b88d4fc463af04fc Align 'e' property of or_d and andor with website spec (Pieter Wuille)
f5deb417804b9f267830bd40177677987df4526d Various additional explanations of the satisfaction logic from Pieter (Pieter Wuille)
22c5b00345063bdeb8b6d3da8b5692d18f92bfb7 miniscript: satisfaction support (Antoine Poinsot)

Pull request description:

  This makes the Miniscript descriptors solvable.

  Note this introduces signing support for much more complex scripts than the wallet was previously able to solve, and the whole tooling isn't provided for a complete Miniscript integration in the wallet. Particularly, the PSBT<->Miniscript integration isn't entirely covered in this PR.

ACKs for top commit:
  achow101:
    ACK 6c7a17a8e0eec377f83ed1399f003ae70b898270
  sipa:
    utACK 6c7a17a8e0eec377f83ed1399f003ae70b898270 (to the extent that it's not my own code).

Tree-SHA512: a71ec002aaf66bd429012caa338fc58384067bcd2f453a46e21d381ed1bacc8e57afb9db57c0fb4bf40de43b30808815e9ebc0ae1fbd9e61df0e7b91a17771cc

1 files changed, 109 insertions, 9 deletions

diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index 70df9ee62c..85589fe86b 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -10,6 +10,7 @@
 #include <policy/policy.h>
 #include <primitives/transaction.h>
 #include <script/keyorigin.h>
+#include <script/miniscript.h>
 #include <script/signingprovider.h>
 #include <script/standard.h>
 #include <uint256.h>
@@ -380,6 +381,92 @@ static CScript PushAll(const std::vector<valtype>& values)
     return result;
 }
 
+template<typename M, typename K, typename V>
+miniscript::Availability MsLookupHelper(const M& map, const K& key, V& value)
+{
+    auto it = map.find(key);
+    if (it != map.end()) {
+        value = it->second;
+        return miniscript::Availability::YES;
+    }
+    return miniscript::Availability::NO;
+}
+
+/**
+ * Context for solving a Miniscript.
+ * If enough material (access to keys, hash preimages, ..) is given, produces a valid satisfaction.
+ */
+struct Satisfier {
+    typedef CPubKey Key;
+
+    const SigningProvider& m_provider;
+    SignatureData& m_sig_data;
+    const BaseSignatureCreator& m_creator;
+    const CScript& m_witness_script;
+
+    explicit Satisfier(const SigningProvider& provider LIFETIMEBOUND, SignatureData& sig_data LIFETIMEBOUND,
+                       const BaseSignatureCreator& creator LIFETIMEBOUND,
+                       const CScript& witscript LIFETIMEBOUND) : m_provider(provider),
+                                                                 m_sig_data(sig_data),
+                                                                 m_creator(creator),
+                                                                 m_witness_script(witscript) {}
+
+    static bool KeyCompare(const Key& a, const Key& b) {
+        return a < b;
+    }
+
+    //! Conversion from a raw public key.
+    template <typename I>
+    std::optional<Key> FromPKBytes(I first, I last) const
+    {
+        Key pubkey{first, last};
+        if (pubkey.IsValid()) return pubkey;
+        return {};
+    }
+
+    //! Conversion from a raw public key hash.
+    template<typename I>
+    std::optional<Key> FromPKHBytes(I first, I last) const {
+        assert(last - first == 20);
+        Key pubkey;
+        CKeyID key_id;
+        std::copy(first, last, key_id.begin());
+        if (GetPubKey(m_provider, m_sig_data, key_id, pubkey)) return pubkey;
+        m_sig_data.missing_pubkeys.push_back(key_id);
+        return {};
+    }
+
+    //! Conversion to raw public key.
+    std::vector<unsigned char> ToPKBytes(const CPubKey& key) const { return {key.begin(), key.end()}; }
+
+    //! Satisfy a signature check.
+    miniscript::Availability Sign(const CPubKey& key, std::vector<unsigned char>& sig) const {
+        if (CreateSig(m_creator, m_sig_data, m_provider, sig, key, m_witness_script, SigVersion::WITNESS_V0)) {
+            return miniscript::Availability::YES;
+        }
+        return miniscript::Availability::NO;
+    }
+
+    //! Time lock satisfactions.
+    bool CheckAfter(uint32_t value) const { return m_creator.Checker().CheckLockTime(CScriptNum(value)); }
+    bool CheckOlder(uint32_t value) const { return m_creator.Checker().CheckSequence(CScriptNum(value)); }
+
+
+    //! Hash preimage satisfactions.
+    miniscript::Availability SatSHA256(const std::vector<unsigned char>& hash, std::vector<unsigned char>& preimage) const {
+        return MsLookupHelper(m_sig_data.sha256_preimages, hash, preimage);
+    }
+    miniscript::Availability SatRIPEMD160(const std::vector<unsigned char>& hash, std::vector<unsigned char>& preimage) const {
+        return MsLookupHelper(m_sig_data.ripemd160_preimages, hash, preimage);
+    }
+    miniscript::Availability SatHASH256(const std::vector<unsigned char>& hash, std::vector<unsigned char>& preimage) const {
+        return MsLookupHelper(m_sig_data.hash256_preimages, hash, preimage);
+    }
+    miniscript::Availability SatHASH160(const std::vector<unsigned char>& hash, std::vector<unsigned char>& preimage) const {
+        return MsLookupHelper(m_sig_data.hash160_preimages, hash, preimage);
+    }
+};
+
 bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreator& creator, const CScript& fromPubKey, SignatureData& sigdata)
 {
     if (sigdata.complete) return true;
@@ -415,9 +502,21 @@ bool ProduceSignature(const SigningProvider& provider, const BaseSignatureCreato
     {
         CScript witnessscript(result[0].begin(), result[0].end());
         sigdata.witness_script = witnessscript;
-        TxoutType subType;
+
+        TxoutType subType{TxoutType::NONSTANDARD};
         solved = solved && SignStep(provider, creator, witnessscript, result, subType, SigVersion::WITNESS_V0, sigdata) && subType != TxoutType::SCRIPTHASH && subType != TxoutType::WITNESS_V0_SCRIPTHASH && subType != TxoutType::WITNESS_V0_KEYHASH;
+
+        // If we couldn't find a solution with the legacy satisfier, try satisfying the script using Miniscript.
+        // Note we need to check if the result stack is empty before, because it might be used even if the Script
+        // isn't fully solved. For instance the CHECKMULTISIG satisfaction in SignStep() pushes partial signatures
+        // and the extractor relies on this behaviour to combine witnesses.
+        if (!solved && result.empty()) {
+            Satisfier ms_satisfier{provider, sigdata, creator, witnessscript};
+            const auto ms = miniscript::FromScript(witnessscript, ms_satisfier);
+            solved = ms && ms->Satisfy(ms_satisfier, result) == miniscript::Availability::YES;
+        }
         result.push_back(std::vector<unsigned char>(witnessscript.begin(), witnessscript.end()));
+
         sigdata.scriptWitness.stack = result;
         sigdata.witness = true;
         result.clear();
@@ -563,26 +662,25 @@ void SignatureData::MergeSignatureData(SignatureData sigdata)
     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)
+bool SignSignature(const SigningProvider &provider, const CScript& fromPubKey, CMutableTransaction& txTo, unsigned int nIn, const CAmount& amount, int nHashType, SignatureData& sig_data)
 {
     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);
+    bool ret = ProduceSignature(provider, creator, fromPubKey, sig_data);
+    UpdateInput(txTo.vin.at(nIn), sig_data);
     return ret;
 }
 
-bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType)
+bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom, CMutableTransaction& txTo, unsigned int nIn, int nHashType, SignatureData& sig_data)
 {
     assert(nIn < txTo.vin.size());
     const 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);
+    return SignSignature(provider, txout.scriptPubKey, txTo, nIn, txout.nValue, nHashType, sig_data);
 }
 
 namespace {
@@ -591,8 +689,10 @@ class DummySignatureChecker final : public BaseSignatureChecker
 {
 public:
     DummySignatureChecker() = default;
-    bool CheckECDSASignature(const std::vector<unsigned char>& scriptSig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override { return true; }
-    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror) const override { return true; }
+    bool CheckECDSASignature(const std::vector<unsigned char>& sig, const std::vector<unsigned char>& vchPubKey, const CScript& scriptCode, SigVersion sigversion) const override { return sig.size() != 0; }
+    bool CheckSchnorrSignature(Span<const unsigned char> sig, Span<const unsigned char> pubkey, SigVersion sigversion, ScriptExecutionData& execdata, ScriptError* serror) const override { return sig.size() != 0; }
+    bool CheckLockTime(const CScriptNum& nLockTime) const override { return true; }
+    bool CheckSequence(const CScriptNum& nSequence) const override { return true; }
 };
 }