How do we know which co-signer signature is in raw hex in multisig?

Question

I have a raw 2of3 multisig transaction. In this transaction, one co-signer already signed. The signature is for only one input.

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

after decoding the transaction, I have the following public keys:

03556117b3f9a92f2997529af415c2c07185b872ddf1439995eca7f3acb65c5882
03917f2527fc394ae2da48ce0148d29e5b756c4d9d180a6762bbe7abe215b29a56
03f03364c624889c99059902524bcd8e2b24fb09cceb2e0f895d6475ef49136765

and this signature:

['OP_0', '304402201b83bd2209bc101736f60eeec3bcc1f79d45019d1829af97f5bd3210e8d8d786022020954c15372268d299b5463e1335595221e16222aee0291509a2098a0eb7fe8041', 'OP_PUSHDATA1', 'OP_VERIFY', 'OP_2', '03556117b3f9a92f2997529af415c2c07185b872ddf1439995eca7f3acb65c5882', '03917f2527fc394ae2da48ce0148d29e5b756c4d9d180a6762bbe7abe215b29a56', '03f03364c624889c99059902524bcd8e2b24fb09cceb2e0f895d6475ef49136765', 'OP_3', 'OP_CHECKMULTISIG']

I have xPubs of all co-signers. How do I know which co-signer signed the transaction?

Answer 1

The only way to know which signers signed is to verify the signatures against the public keys. Each signature will only verify with one of the pubkeys.