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In a pay 2 script hash transaction, does the redeem script get checked for valid public keys before a transaction can be signed? I have noticed that if I have a redeem script with one invalid pubkey out of 3, even if I sign with a valid private key for the multi-sig transaction, the "scriptSig" is blank and the hex returned for the signrawtransaction is small/incomplete.

Any ideas?

I saw a comment on here that led me to believe that public keys in redeem scripts could be text or 'anything'

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  • Get checked by what? What code/project are you using to sign transactions?
    – Pieter Wuille
    Commented Jan 17, 2017 at 13:21
  • I am using bitcoin-cli
    – Derek
    Commented Jan 17, 2017 at 16:57

2 Answers 2

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For m of n multisig, only the last m pub keys are checked for validity, given that at least the last m pub keys are valid public keys and match to signatures in the correct order. Other pub keys are not checked and can be used to push arbitrary data.

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You are doing something wrong. (or your tool is broken)

Signing the input can not leave scriptSig blank

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  • the tool is bitcoin-cli. I can reproduce steps in my question later if needed, but if you want to try - run createmultisig then modify one of the public keys that is in the redeemscript. Send btc to the multi address. Create a 3rd party and try to send to that user. Sign the "send" transaction with the modifed redeemScript, and you'll see that scriptSig is blank
    – Derek
    Commented Jan 17, 2017 at 17:00
  • If you modify one of the keys, the corresponding address will change. Bitcoin Core cannot even know how to sign for it without knowing that.
    – Pieter Wuille
    Commented Jan 17, 2017 at 17:28
  • Are you saying that the signature part re-creates the mutlisign address using the keys that are found in the "corrupt" redeemScript? I would have thought that was encoded in the transaction that was created using the real redeemScript
    – Derek
    Commented Jan 17, 2017 at 17:30
  • I think what @PieterWuille means, and correct me if I'm wrong, is that if you modify one of the public keys used to create the redeemScipt, the reddemScript itself changes, that is: the address format for P2SH according to BIP13 is [one-byte version][20-byte hash][4-byte checksum], since the 20 byte hash represents the hash of the scrip you have created, lets say its a 1-3 multisig address like: address = 1 <PubKey1><PubKey2><PubKey3> 3, if you change, for example PubKey2 for a new one: address2 = 1 <PubKey1><PubKey4><PubKey3> 3, the resulting script will change (address != address2).
    – sr_gi
    Commented Feb 16, 2017 at 11:55

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