op_checkmultisig: Last signature is not verified about programmingbitcoin

[mattacus]

Here is the way I went about it, I saw that about the signatures being in the same order of the pubkeys.
But, I'm not quite sure why that is necessary so long as:

1. Each signature can be verified against one of the pubkeys successfully, and
2. The pubkey is removed from the list once it is matched with a signature

I solved it using list .remove(). I don't think things necessarily have to be in order. It seems to cover all the test cases I've tried. Am I missing something or would this work just as well?

try:
        pubkeys_parsed = [S256Point.parse(p) for p in sec_pubkeys]
        signatures_parsed = [Signature.parse(p) for p in signatures]
        for sig in signatures_parsed:
            if len(pubkeys_parsed) == 0:
                return False
            signature_verified = False
            for pubkey in pubkeys_parsed:
                if pubkey.verify(z, sig):
                    print(f'Verified point: {pubkey} with signature: {sig}')
                    signature_verified = True
                    pubkeys_parsed.remove(pubkey)
                    break
            if not signature_verified:
                return False  # Signature did not match a pubkey
        stack.append(encode_num(1))

[koirikivi]

@mattacus From my understanding, the actual implementation of op_checkmultisig in Bitcoin requires the signatures and pubkeys to be in the same order. At least according to these sources:

• https://bitcoin.stackexchange.com/questions/113425/order-of-signatures-in-multisig-scheme
• https://en.bitcoin.it/wiki/OP_CHECKMULTISIG

[mattacus]

Right, I saw that, in the docs:

Because public keys are not checked again if they fail any signature comparison, signatures must be placed in the scriptSig using the same order as their corresponding public keys

After thinking about it some more it makes more sense to do it that way since signature verification time could add up if you have, say, 100s of signature that each node must verify, and you don't pop each pubkey each time it is visited. (In my case I am removing them, but only if the signature is verified, so there could be more iterations). So it seems like they chose that approach for efficiency reasons.