Merge bitcoin/bitcoin#25664: refactor: Redefine `IsSolvable()` using descriptors

b16f93caddcd3254eaf3dc43e09adf2142a9c40a script/sign: remove needless IsSolvable() utility (Antoine Poinsot)
c232ef20c0fd2e3b55355e52684091cad3af5247 outputtype: remove redundant check for uncompressed keys in AddAndGetDestinationForScript (Antoine Poinsot)

Pull request description:

  Now that we have descriptors there is no need to try to sign for a scriptPubKey using dummy signatures, and using a mocked verification of this witness against the interpreter, just to make sure we know how to spend such a Script. Just try to infer a solvable descriptor: any scriptPubKey that we can sign for can be inferred as such.

  This came up in #24149 but i think it's worth it on its own.

ACKs for top commit:
  instagibbs:
    ACK https://github.com/bitcoin/bitcoin/pull/25664/commits/b16f93caddcd3254eaf3dc43e09adf2142a9c40a
  achow101:
    re-ACK b16f93caddcd3254eaf3dc43e09adf2142a9c40a
  furszy:
    ACK b16f93ca, only change is the `IsSolvable` helper function removal.

Tree-SHA512: 137068157ce90210b710b1bf9ac3c400e2ff5af1112f892094b69875ea473d6a899f52adb51e5030cb907dee517602059cd1661107808558efa5de842ba12b41

2 files changed, 0 insertions, 25 deletions

diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index 79cf918c9b..4014ebadbc 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -632,25 +632,6 @@ public:
 const BaseSignatureCreator& DUMMY_SIGNATURE_CREATOR = DummySignatureCreator(32, 32);
 const BaseSignatureCreator& DUMMY_MAXIMUM_SIGNATURE_CREATOR = DummySignatureCreator(33, 32);
 
-bool IsSolvable(const SigningProvider& provider, const CScript& script)
-{
-    // This check is to make sure that the script we created can actually be solved for and signed by us
-    // if we were to have the private keys. This is just to make sure that the script is valid and that,
-    // if found in a transaction, we would still accept and relay that transaction. In particular,
-    // it will reject witness outputs that require signing with an uncompressed public key.
-    SignatureData sigs;
-    // Make sure that STANDARD_SCRIPT_VERIFY_FLAGS includes SCRIPT_VERIFY_WITNESS_PUBKEYTYPE, the most
-    // important property this function is designed to test for.
-    static_assert(STANDARD_SCRIPT_VERIFY_FLAGS & SCRIPT_VERIFY_WITNESS_PUBKEYTYPE, "IsSolvable requires standard script flags to include WITNESS_PUBKEYTYPE");
-    if (ProduceSignature(provider, DUMMY_SIGNATURE_CREATOR, script, sigs)) {
-        // VerifyScript check is just defensive, and should never fail.
-        bool verified = VerifyScript(sigs.scriptSig, script, &sigs.scriptWitness, STANDARD_SCRIPT_VERIFY_FLAGS, DUMMY_CHECKER);
-        assert(verified);
-        return true;
-    }
-    return false;
-}
-
 bool IsSegWitOutput(const SigningProvider& provider, const CScript& script)
 {
     int version;
diff --git a/src/script/sign.h b/src/script/sign.h
index 5e58272154..958d673b9f 100644
--- a/src/script/sign.h
+++ b/src/script/sign.h
@@ -97,12 +97,6 @@ bool SignSignature(const SigningProvider &provider, const CTransaction& txFrom,
 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
- * have all private keys. While this function does not need private keys, the passed
- * provider is used to look up public keys and redeemscripts by hash.
- * Solvability is unrelated to whether we consider this output to be ours. */
-bool IsSolvable(const SigningProvider& provider, const CScript& script);
-
 /** Check whether a scriptPubKey is known to be segwit. */
 bool IsSegWitOutput(const SigningProvider& provider, const CScript& script);