TIL: while it’s pretty easy to sign a message for a single-sig address, there’s no easy equivalent for a multisig address. #Bitcoin
Discussion
Is it not possible or is it that it's possible just no clients have implemented support for partial signing like that?
Yeah wait I thought its just as easy to do in various clients like Bitcoin core, Sparrow & Blue wallet?
Now I need to test
Consider a 2-of-3 multisig address. You can sign a message using any of the 3 keys. But the 2-of-3 address itself is the hash of a script demanding proof from a combination of keys.
So to “sign” a multisig address (P2SH, bc1q…), you have to reveal the script, which reveals the pubkey hashes, then you can sign the message with a quorum of signers.
One could theoretically design a UX for this. Two UXs really—one for the signer and one for the verifier. But to my knowledge, no smooth UX currently exists.
Yeah that took me by surprise too when I learned that couldn't sign a message proving ownership of a multisig address.
Bitcoin talk forum explaining that it is impossible (in 2016).
https://bitcointalk.org/index.php?topic=1576803.0
Then more recently (2021) Craig raw explaining why it is currently not a feature.
https://github.com/sparrowwallet/sparrow/issues/193#issuecomment-1117139854