1

I have a technical question regarding the signrawtransaction function in Bitcoin core when signing a partially-signed transaction.

I have tested different scenarios and signrawtransaction will always sort the signatures in the correct way in the scriptSig, regardless of the order the transaction is signed one-by-one.

Is this achieved by analyzing the scriptSig of the partially-signed transaction when signing, and then verifying each signature in the partially-signed transactions scriptSig against all public keys in the redeemscript and finally ordering them correctly? Or is there a better way of doing this?

Unfortunately I don't understand how this is done by reading the C-code of bitcoin core.

1 Answer 1

5

The signatures must be ordered the same way as public keys. Otherwize transaction is invalid. This is how OP_CHECKMULTISIG(VERIFY) works.

Of course, you may use the private keys for signing in any order, because signatures are independent.

6
  • Thanks for your answer. I know that the order in the final scriptSig must regard the redeemScript. But does the Bitcoin Core signrawtransaction-function deserialize the partially-signed scriptSig and order the signatures accordingly? This is done by actually running the verify-signature algorithm on each provided signature and each possible public-key from the redeemScript? Oct 6, 2017 at 10:00
  • E.g.: with a 2-of-3 multisig (A,B,C), we first sign the newly created raw transaction with public-key C. Now this partially-signed tx is signed with public key B. To place the signature of B in the partially signed scriptSig containing signature of C, signrawtransaction must first check to which public-key the already given signature belongs to know if the signature of B has to be placed before or after? Oct 6, 2017 at 10:01
  • 1
    >>>...by actually running the verify-signature algorithm on each provided signature and each possible public-key from the redeemScript? <<< Yes. github.com/bitcoin/bitcoin/blob/master/src/script/sign.cpp#L228
    – amaclin
    Oct 6, 2017 at 11:30
  • In fact you can implement your own algorithm for signing multisig transactions. You may use some "placeholders" and replace them with signatures later. Format of raw unsigned transaction is not a consensus rule :)
    – amaclin
    Oct 6, 2017 at 11:37
  • Thanks! I am implementing the signing function in another program and want to keep compatibility with the way that Core is signing multisig. Your information has helped me a lot! Oct 6, 2017 at 11:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.