merge bitcoin#20867: Support up to 20 keys for multisig under Segwit context

Author: kwvg

src/rpc/util.cpp

@@ -277,8 +277,8 @@ CTxDestination AddAndGetMultisigDestination(const int required, const std::vecto
     if ((int)pubkeys.size() < required) {
         throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("not enough keys supplied (got %u keys, but need at least %d to redeem)", pubkeys.size(), required));
     }
-    if (pubkeys.size() > 16) {
-        throw JSONRPCError(RPC_INVALID_PARAMETER, "Number of keys involved in the multisignature address creation > 16\nReduce the number");
+    if (pubkeys.size() > MAX_PUBKEYS_PER_MULTISIG) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Number of keys involved in the multisignature address creation > %d\nReduce the number", MAX_PUBKEYS_PER_MULTISIG));
     }
 
     script_out = GetScriptForMultisig(required, pubkeys);

src/script/descriptor.cpp

@@ -978,8 +978,8 @@ std::unique_ptr<DescriptorImpl> ParseScript(uint32_t& key_exp_index, Span<const
             providers.emplace_back(std::move(pk));
             key_exp_index++;
         }
-        if (providers.empty() || providers.size() > 16) {
-            error = strprintf("Cannot have %u keys in multisig; must have between 1 and 16 keys, inclusive", providers.size());
+        if (providers.empty() || providers.size() > MAX_PUBKEYS_PER_MULTISIG) {
+            error = strprintf("Cannot have %u keys in multisig; must have between 1 and %d keys, inclusive", providers.size(), MAX_PUBKEYS_PER_MULTISIG);
             return nullptr;
         } else if (thres < 1) {
             error = strprintf("Multisig threshold cannot be %d, must be at least 1", thres);
@@ -995,6 +995,7 @@ std::unique_ptr<DescriptorImpl> ParseScript(uint32_t& key_exp_index, Span<const
             }
         }
         if (ctx == ParseScriptContext::P2SH) {
+            // This limits the maximum number of compressed pubkeys to 15.
             if (script_size + 3 > MAX_SCRIPT_ELEMENT_SIZE) {
                 error = strprintf("P2SH script is too large, %d bytes is larger than %d bytes", script_size + 3, MAX_SCRIPT_ELEMENT_SIZE);
                 return nullptr;

src/script/interpreter.cpp

@@ -221,7 +221,7 @@ bool static CheckPubKeyEncoding(const valtype &vchPubKey, unsigned int flags, co
     return true;
 }
 
-bool static CheckMinimalPush(const valtype& data, opcodetype opcode) {
+bool CheckMinimalPush(const valtype& data, opcodetype opcode) {
     // Excludes OP_1NEGATE, OP_1-16 since they are by definition minimal
     assert(0 <= opcode && opcode <= OP_PUSHDATA4);
     if (data.size() == 0) {

src/script/interpreter.h

@@ -179,6 +179,8 @@ using MutableTransactionSignatureChecker = GenericTransactionSignatureChecker<CM
 bool EvalScript(std::vector<std::vector<unsigned char> >& stack, const CScript& script, unsigned int flags, const BaseSignatureChecker& checker, SigVersion sigversion, ScriptError* error = nullptr);
 bool VerifyScript(const CScript& scriptSig, const CScript& scriptPubKey, unsigned int flags, const BaseSignatureChecker& checker, ScriptError* error = nullptr);
 
+bool CheckMinimalPush(const std::vector<unsigned char>& data, opcodetype opcode);
+
 int FindAndDelete(CScript& script, const CScript& b);
 
 #endif // BITCOIN_SCRIPT_INTERPRETER_H

src/script/standard.cpp

@@ -70,21 +70,53 @@ static constexpr bool IsSmallInteger(opcodetype opcode)
     return opcode >= OP_1 && opcode <= OP_16;
 }
 
-static bool MatchMultisig(const CScript& script, unsigned int& required, std::vector<valtype>& pubkeys)
+static constexpr bool IsPushdataOp(opcodetype opcode)
+{
+    return opcode > OP_FALSE && opcode <= OP_PUSHDATA4;
+}
+
+static constexpr bool IsValidMultisigKeyCount(int n_keys)
+{
+    return n_keys > 0 && n_keys <= MAX_PUBKEYS_PER_MULTISIG;
+}
+
+static bool GetMultisigKeyCount(opcodetype opcode, valtype data, int& count)
+{
+    if (IsSmallInteger(opcode)) {
+        count = CScript::DecodeOP_N(opcode);
+        return IsValidMultisigKeyCount(count);
+    }
+
+    if (IsPushdataOp(opcode)) {
+        if (!CheckMinimalPush(data, opcode)) return false;
+        try {
+            count = CScriptNum(data, /* fRequireMinimal = */ true).getint();
+            return IsValidMultisigKeyCount(count);
+        } catch (const scriptnum_error&) {
+            return false;
+        }
+    }
+
+    return false;
+}
+
+static bool MatchMultisig(const CScript& script, int& required_sigs, std::vector<valtype>& pubkeys)
 {
     opcodetype opcode;
     valtype data;
+    int num_keys;
+
     CScript::const_iterator it = script.begin();
     if (script.size() < 1 || script.back() != OP_CHECKMULTISIG) return false;
 
-    if (!script.GetOp(it, opcode, data) || !IsSmallInteger(opcode)) return false;
-    required = CScript::DecodeOP_N(opcode);
+    if (!script.GetOp(it, opcode, data) || !GetMultisigKeyCount(opcode, data, required_sigs)) return false;
     while (script.GetOp(it, opcode, data) && CPubKey::ValidSize(data)) {
         pubkeys.emplace_back(std::move(data));
     }
-    if (!IsSmallInteger(opcode)) return false;
-    unsigned int keys = CScript::DecodeOP_N(opcode);
-    if (pubkeys.size() != keys || keys < required) return false;
+    if (!GetMultisigKeyCount(opcode, data, num_keys)) return false;
+
+    if (pubkeys.size() != static_cast<unsigned long>(num_keys) || num_keys < required_sigs) return false;
+
     return (it + 1 == script.end());
 }
 
@@ -121,12 +153,12 @@ TxoutType Solver(const CScript& scriptPubKey, std::vector<std::vector<unsigned c
         return TxoutType::PUBKEYHASH;
     }
 
-    unsigned int required;
+    int required;
     std::vector<std::vector<unsigned char>> keys;
     if (MatchMultisig(scriptPubKey, required, keys)) {
-        vSolutionsRet.push_back({static_cast<unsigned char>(required)}); // safe as required is in range 1..16
+        vSolutionsRet.push_back({static_cast<unsigned char>(required)}); // safe as required is in range 1..20
         vSolutionsRet.insert(vSolutionsRet.end(), keys.begin(), keys.end());
-        vSolutionsRet.push_back({static_cast<unsigned char>(keys.size())}); // safe as size is in range 1..16
+        vSolutionsRet.push_back({static_cast<unsigned char>(keys.size())}); // safe as size is in range 1..20
         return TxoutType::MULTISIG;
     }
 
@@ -240,10 +272,11 @@ CScript GetScriptForMultisig(int nRequired, const std::vector<CPubKey>& keys)
 {
     CScript script;
 
-    script << CScript::EncodeOP_N(nRequired);
+    script << nRequired;
     for (const CPubKey& key : keys)
         script << ToByteVector(key);
-    script << CScript::EncodeOP_N(keys.size()) << OP_CHECKMULTISIG;
+    script << keys.size() << OP_CHECKMULTISIG;
+
     return script;
 }
 

src/test/descriptor_tests.cpp

@@ -2,6 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
+#include <pubkey.h>
 #include <script/descriptor.h>
 #include <script/sign.h>
 #include <script/standard.h>
@@ -27,6 +28,14 @@ void CheckUnparsable(const std::string& prv, const std::string& pub, const std::
     BOOST_CHECK_EQUAL(error, expected_error);
 }
 
+/** Check that the script is inferred as non-standard */
+void CheckInferRaw(const CScript& script)
+{
+    FlatSigningProvider dummy_provider;
+    std::unique_ptr<Descriptor> desc = InferDescriptor(script, dummy_provider);
+    BOOST_CHECK(desc->ToString().rfind("raw(", 0) == 0);
+}
+
 constexpr int DEFAULT = 0;
 constexpr int RANGE = 1; // Expected to be ranged descriptor
 constexpr int HARDENED = 2; // Derivation needs access to private keys
@@ -327,8 +336,7 @@ BOOST_AUTO_TEST_CASE(descriptor_test)
     CheckUnparsable("multi(0,L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1,5KYZdUEo39z3FPrtuX2QbbwGnNP5zTd7yyr2SC1j299sBCnWjss)", "multi(0,03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd,04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235)", "Multisig threshold cannot be 0, must be at least 1"); // Threshold of 0
     CheckUnparsable("multi(3,L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1,5KYZdUEo39z3FPrtuX2QbbwGnNP5zTd7yyr2SC1j299sBCnWjss)", "multi(3,03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd,04a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd5b8dec5235a0fa8722476c7709c02559e3aa73aa03918ba2d492eea75abea235)", "Multisig threshold cannot be larger than the number of keys; threshold is 3 but only 2 keys specified"); // Threshold larger than number of keys
     CheckUnparsable("multi(3,KzoAz5CanayRKex3fSLQ2BwJpN7U52gZvxMyk78nDMHuqrUxuSJy,KwGNz6YCCQtYvFzMtrC6D3tKTKdBBboMrLTsjr2NYVBwapCkn7Mr,KxogYhiNfwxuswvXV66eFyKcCpm7dZ7TqHVqujHAVUjJxyivxQ9X,L2BUNduTSyZwZjwNHynQTF14mv2uz2NRq5n5sYWTb4FkkmqgEE9f)", "multi(3,03669b8afcec803a0d323e9a17f3ea8e68e8abe5a278020a929adbec52421adbd0,0260b2003c386519fc9eadf2b5cf124dd8eea4c4e68d5e154050a9346ea98ce600,0362a74e399c39ed5593852a30147f2959b56bb827dfa3e60e464b02ccf87dc5e8,0261345b53de74a4d721ef877c255429961b7e43714171ac06168d7e08c542a8b8)", "Cannot have 4 pubkeys in bare multisig; only at most 3 pubkeys"); // Threshold larger than number of keys
-    CheckUnparsable("sh(multi(16,KzoAz5CanayRKex3fSLQ2BwJpN7U52gZvxMyk78nDMHuqrUxuSJy,KwGNz6YCCQtYvFzMtrC6D3tKTKdBBboMrLTsjr2NYVBwapCkn7Mr,KxogYhiNfwxuswvXV66eFyKcCpm7dZ7TqHVqujHAVUjJxyivxQ9X,L2BUNduTSyZwZjwNHynQTF14mv2uz2NRq5n5sYWTb4FkkmqgEE9f,L1okJGHGn1kFjdXHKxXjwVVtmCMR2JA5QsbKCSpSb7ReQjezKeoD,KxDCNSST75HFPaW5QKpzHtAyaCQC7p9Vo3FYfi2u4dXD1vgMiboK,L5edQjFtnkcf5UWURn6UuuoFrabgDQUHdheKCziwN42aLwS3KizU,KzF8UWFcEC7BYTq8Go1xVimMkDmyNYVmXV5PV7RuDicvAocoPB8i,L3nHUboKG2w4VSJ5jYZ5CBM97oeK6YuKvfZxrefdShECcjEYKMWZ,KyjHo36dWkYhimKmVVmQTq3gERv3pnqA4xFCpvUgbGDJad7eS8WE,KwsfyHKRUTZPQtysN7M3tZ4GXTnuov5XRgjdF2XCG8faAPmFruRF,KzCUbGhN9LJhdeFfL9zQgTJMjqxdBKEekRGZX24hXdgCNCijkkap,KzgpMBwwsDLwkaC5UrmBgCYaBD2WgZ7PBoGYXR8KT7gCA9UTN5a3,KyBXTPy4T7YG4q9tcAM3LkvfRpD1ybHMvcJ2ehaWXaSqeGUxEdkP,KzJDe9iwJRPtKP2F2AoN6zBgzS7uiuAwhWCfGdNeYJ3PC1HNJ8M8,L1xbHrxynrqLKkoYc4qtoQPx6uy5qYXR5ZDYVYBSRmCV5piU3JG9,L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1))","sh(multi(16,03669b8afcec803a0d323e9a17f3ea8e68e8abe5a278020a929adbec52421adbd0,0260b2003c386519fc9eadf2b5cf124dd8eea4c4e68d5e154050a9346ea98ce600,0362a74e399c39ed5593852a30147f2959b56bb827dfa3e60e464b02ccf87dc5e8,0261345b53de74a4d721ef877c255429961b7e43714171ac06168d7e08c542a8b8,02da72e8b46901a65d4374fe6315538d8f368557dda3a1dcf9ea903f3afe7314c8,0318c82dd0b53fd3a932d16e0ba9e278fcc937c582d5781be626ff16e201f72286,0297ccef1ef99f9d73dec9ad37476ddb232f1238aff877af19e72ba04493361009,02e502cfd5c3f972fe9a3e2a18827820638f96b6f347e54d63deb839011fd5765d,03e687710f0e3ebe81c1037074da939d409c0025f17eb86adb9427d28f0f7ae0e9,02c04d3a5274952acdbc76987f3184b346a483d43be40874624b29e3692c1df5af,02ed06e0f418b5b43a7ec01d1d7d27290fa15f75771cb69b642a51471c29c84acd,036d46073cbb9ffee90473f3da429abc8de7f8751199da44485682a989a4bebb24,02f5d1ff7c9029a80a4e36b9a5497027ef7f3e73384a4a94fbfe7c4e9164eec8bc,02e41deffd1b7cce11cde209a781adcffdabd1b91c0ba0375857a2bfd9302419f3,02d76625f7956a7fc505ab02556c23ee72d832f1bac391bcd2d3abce5710a13d06,0399eb0a5487515802dc14544cf10b3666623762fbed2ec38a3975716e2c29c232,03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))", "Cannot have 17 keys in multisig; must have between 1 and 16 keys, inclusive"); // Cannot have more than 16 keys in a multisig
-
+    CheckUnparsable("sh(multi(16,KzoAz5CanayRKex3fSLQ2BwJpN7U52gZvxMyk78nDMHuqrUxuSJy,KwGNz6YCCQtYvFzMtrC6D3tKTKdBBboMrLTsjr2NYVBwapCkn7Mr,KxogYhiNfwxuswvXV66eFyKcCpm7dZ7TqHVqujHAVUjJxyivxQ9X,L2BUNduTSyZwZjwNHynQTF14mv2uz2NRq5n5sYWTb4FkkmqgEE9f,L1okJGHGn1kFjdXHKxXjwVVtmCMR2JA5QsbKCSpSb7ReQjezKeoD,KxDCNSST75HFPaW5QKpzHtAyaCQC7p9Vo3FYfi2u4dXD1vgMiboK,L5edQjFtnkcf5UWURn6UuuoFrabgDQUHdheKCziwN42aLwS3KizU,KzF8UWFcEC7BYTq8Go1xVimMkDmyNYVmXV5PV7RuDicvAocoPB8i,L3nHUboKG2w4VSJ5jYZ5CBM97oeK6YuKvfZxrefdShECcjEYKMWZ,KyjHo36dWkYhimKmVVmQTq3gERv3pnqA4xFCpvUgbGDJad7eS8WE,KwsfyHKRUTZPQtysN7M3tZ4GXTnuov5XRgjdF2XCG8faAPmFruRF,KzCUbGhN9LJhdeFfL9zQgTJMjqxdBKEekRGZX24hXdgCNCijkkap,KzgpMBwwsDLwkaC5UrmBgCYaBD2WgZ7PBoGYXR8KT7gCA9UTN5a3,KyBXTPy4T7YG4q9tcAM3LkvfRpD1ybHMvcJ2ehaWXaSqeGUxEdkP,KzJDe9iwJRPtKP2F2AoN6zBgzS7uiuAwhWCfGdNeYJ3PC1HNJ8M8,L1xbHrxynrqLKkoYc4qtoQPx6uy5qYXR5ZDYVYBSRmCV5piU3JG9,L4rK1yDtCWekvXuE6oXD9jCYfFNV2cWRpVuPLBcCU2z8TrisoyY1))","sh(multi(16,03669b8afcec803a0d323e9a17f3ea8e68e8abe5a278020a929adbec52421adbd0,0260b2003c386519fc9eadf2b5cf124dd8eea4c4e68d5e154050a9346ea98ce600,0362a74e399c39ed5593852a30147f2959b56bb827dfa3e60e464b02ccf87dc5e8,0261345b53de74a4d721ef877c255429961b7e43714171ac06168d7e08c542a8b8,02da72e8b46901a65d4374fe6315538d8f368557dda3a1dcf9ea903f3afe7314c8,0318c82dd0b53fd3a932d16e0ba9e278fcc937c582d5781be626ff16e201f72286,0297ccef1ef99f9d73dec9ad37476ddb232f1238aff877af19e72ba04493361009,02e502cfd5c3f972fe9a3e2a18827820638f96b6f347e54d63deb839011fd5765d,03e687710f0e3ebe81c1037074da939d409c0025f17eb86adb9427d28f0f7ae0e9,02c04d3a5274952acdbc76987f3184b346a483d43be40874624b29e3692c1df5af,02ed06e0f418b5b43a7ec01d1d7d27290fa15f75771cb69b642a51471c29c84acd,036d46073cbb9ffee90473f3da429abc8de7f8751199da44485682a989a4bebb24,02f5d1ff7c9029a80a4e36b9a5497027ef7f3e73384a4a94fbfe7c4e9164eec8bc,02e41deffd1b7cce11cde209a781adcffdabd1b91c0ba0375857a2bfd9302419f3,02d76625f7956a7fc505ab02556c23ee72d832f1bac391bcd2d3abce5710a13d06,0399eb0a5487515802dc14544cf10b3666623762fbed2ec38a3975716e2c29c232,03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd))", "P2SH script is too large, 581 bytes is larger than 520 bytes"); // Cannot have more than 15 keys in a P2SH multisig, or we exceed maximum push size
     // Check for invalid nesting of structures
     CheckUnparsable("sh(XJvEUEcFWCHCyruc8ZX5exPZaGe4UR7gC5FHrhwPnQGDs1uWCsT2)", "sh(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd)", "A function is needed within P2SH"); // P2SH needs a script, not a key
     CheckUnparsable("sh(sh(pk(XJvEUEcFWCHCyruc8ZX5exPZaGe4UR7gC5FHrhwPnQGDs1uWCsT2)))", "sh(sh(pk(03a34b99f22c790c4e36b2b3c2c35a36db06226e41c692fc82b8b56ac1c540c5bd)))", "Can only have sh() at top level"); // Cannot embed P2SH inside P2SH
@@ -346,6 +354,27 @@ BOOST_AUTO_TEST_CASE(descriptor_test)
     CheckUnparsable("", "addr(asdf)", "Address is not valid"); // Invalid address
     CheckUnparsable("", "raw(asdf)", "Raw script is not hex"); // Invalid script
     CheckUnparsable("", "raw(Ü)#00000000", "Invalid characters in payload"); // Invalid chars
+
+    // A 2of4 but using a direct push rather than OP_2
+    CScript nonminimalmultisig;
+    CKey keys[4];
+    nonminimalmultisig << std::vector<unsigned char>{2};
+    for (int i = 0; i < 4; i++) {
+        keys[i].MakeNewKey(true);
+        nonminimalmultisig << ToByteVector(keys[i].GetPubKey());
+    }
+    nonminimalmultisig << 4 << OP_CHECKMULTISIG;
+    CheckInferRaw(nonminimalmultisig);
+
+    // A 2of4 but using a direct push rather than OP_4
+    nonminimalmultisig.clear();
+    nonminimalmultisig << 2;
+    for (int i = 0; i < 4; i++) {
+        keys[i].MakeNewKey(true);
+        nonminimalmultisig << ToByteVector(keys[i].GetPubKey());
+    }
+    nonminimalmultisig << std::vector<unsigned char>{4} << OP_CHECKMULTISIG;
+    CheckInferRaw(nonminimalmultisig);
 }
 
 BOOST_AUTO_TEST_SUITE_END()

test/functional/wallet_importdescriptors.py

@@ -433,6 +433,42 @@ def run_test(self):
         assert_equal(tx_signed_2['complete'], True)
         self.nodes[1].sendrawtransaction(tx_signed_2['hex'])
 
+
+        self.log.info("Under P2SH, multisig are standard with up to 15 "
+                      "compressed keys")
+        self.nodes[1].createwallet(wallet_name='multi_priv_big_legacy',
+                                   blank=True, descriptors=True)
+        multi_priv_big = self.nodes[1].get_wallet_rpc('multi_priv_big_legacy')
+        xkey = "tprv8ZgxMBicQKsPeZSeYx7VXDDTs3XrTcmZQpRLbAeSQFCQGgKwR4gKpcxHaKdoTNHniv4EPDJNdzA3KxRrrBHcAgth8fU5X4oCndkkxk39iAt/*"
+        xkey_int = "tprv8ZgxMBicQKsPeZSeYx7VXDDTs3XrTcmZQpRLbAeSQFCQGgKwR4gKpcxHaKdoTNHniv4EPDJNdzA3KxRrrBHcAgth8fU5X4oCndkkxk39iAt/1/*"
+        res = multi_priv_big.importdescriptors([
+        {
+            "desc": descsum_create(f"sh(multi(15,{(xkey + ',') * 14}{xkey}))"),
+            "active": True,
+            "range": 1000,
+            "next_index": 0,
+            "timestamp": "now"
+        },
+        {
+            "desc": descsum_create(f"sh(multi(15,{(xkey_int + ',') * 14}{xkey_int}))"),
+            "active": True,
+            "internal": True,
+            "range": 1000,
+            "next_index": 0,
+            "timestamp": "now"
+        }])
+        assert_equal(res[0]['success'], True)
+        assert_equal(res[1]['success'], True)
+
+        addr = multi_priv_big.getnewaddress("")
+        w0.sendtoaddress(addr, 10)
+        self.nodes[0].generate(6)
+        self.sync_all()
+        # It is standard and would relay.
+        txid = multi_priv_big.sendtoaddress(w0.getnewaddress(), 10, "", "",
+                                            True)
+
+
         self.log.info("Combo descriptors cannot be active")
         self.test_importdesc({"desc": descsum_create("combo(tpubDCJtdt5dgJpdhW4MtaVYDhG4T4tF6jcLR1PxL43q9pq1mxvXgMS9Mzw1HnXG15vxUGQJMMSqCQHMTy3F1eW5VkgVroWzchsPD5BUojrcWs8/*)"),
                               "active": True,