# Multisig where one of the keys specifically is required?

Is it possible to make a multisig wallet that requires one of the keys specifically and any of the other ones in order to sign a transaction?

For example, let's say I have a 2-of-3 multisig that has signators A, B, and C. Can I make a multisig that requires that every transaction be signed by A specifically and then one of either of the other keys?

• why does this have the `nbitcoin` tag? looks unrelated May 7, 2018 at 8:56

No, but instead you can make a 3-of-4 multisig where you hold both keys A and B, then you give key C to a family member, and D to someone else(just as an example). This way you are certain that you are involved in all transactions. I presume this is the end result you are after?

• That works and makes sense. Feb 8, 2017 at 12:34
• no need the "D" key. just 3-of-4 of (A+A+B+C) Oct 7, 2017 at 9:16
• ahh, very clever amaclin Oct 8, 2017 at 19:41
• @amaclin Are you saying that sets of private keys in a multisig definition are not required to be unique? Is there is no limitation with regard to repeating a set of private keys in a multisig definition? So with a 3 of 4 wallet, A and B can both be the same set of private keys? May 27 at 2:57

Yes, both of these policies achieve what you are trying to do.

`thresh(2,pk(A),or(pk(B),pk(C)))`

`thresh(2,pk(A),thresh(1,pk(B),pk(C)))`

Each of them use `thresh()` as defined here:

thresh(NUM,POL,POL,...): Require that NUM out of the following subpolicies are met (all combinations are assumed to be equally likely).

• This link is broken. I am trying to setup a multisig wallet using Sparrow. I have tried entering these definitions in the Script Policy Description field but it is throwing an "Invalid output descriptor" error. May 27 at 3:01

There is another solution but it removes the ability to identify who signed the second transaction. Create a 2 of 2 multisig wallet in Electrum. The first signature is yours. The second signature is done via a hardware wallet like Trezor. Clone that Trezor as many times as you want with the recovery seed.