Fix OP_CHECKMULTISIG silently accepting a non-matching signature - #170
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op_checkmultisig's inner loop over remaining pubkeys had no way to detect exhausted every pubkey without a match -- a signature that does not correspond to any provided pubkey was silently treated as optional rather than causing the whole check to fail. A 1-of-1 (or N-of-N) CHECKMULTISIG script would accept any validly-DER-encoded signature regardless of whether it matched the locking pubkey(s) at all, defeating the actual authorization check. Adds a while/else clause: if the inner loop exhausts every remaining point without hitting break, the signature did not match anything and the whole check now correctly returns False. The same underlying flaw exists in the reference implementation this is based on -- see jimmysong/programmingbitcoin#270, open and unfixed there too. Includes a regression test reusing the existing positive tests real transaction fixture, with one signature swapped for a real, validly DER-encoded signature from an unrelated transaction.
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Fixes #169
op_checkmultisig's inner loop over remaining pubkeys had no way to detect exhausted every pubkey without a match -- a signature that does not correspond to any provided pubkey was silently treated as optional rather than causing the whole check to fail. A 1-of-1 (or N-of-N) CHECKMULTISIG script would accept any validly-DER-encoded signature regardless of whether it matched the locking pubkey(s) at all, defeating the actual authorization check.
Adds a while/else clause: if the inner loop exhausts every remaining point without hitting break, the signature did not match anything and the whole check now correctly returns False.
The same underlying flaw exists in the reference implementation this is based on -- see jimmysong/programmingbitcoin#270, open and unfixed there too.
Includes a regression test reusing the existing positive tests real transaction fixture, with one signature swapped for a real, validly DER-encoded signature from an unrelated transaction.