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OP_CHECKMULTISIG

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A Bitcoin Script opcode that verifies M-of-N signatures against a list of public keys embedded in the redeem script. It is the foundation of Legacy and P2SH multisig outputs; P2WSH multisig uses the SegWit-compatible OP_CHECKMULTISIG inside a witness script. A well-known off-by-one bug requires scripts to push a dummy OP_0 element before the signatures; Tapscript replaces this opcode with OP_CHECKSIGADD to fix the issue.