Is multisig wallet simply a combination of many singlesig wallets?

Question

I’m trying to create a multisig wallet for the first time.

My pre-understanding is that multisig wallet is simply a combination of many singlesig address.

So for example I have 3 existing singlesig wallets:

1. electrum wallet
2. Bluewallet
3. Coldcard wallet

Can I just simply use the xpubs of the wallets to create a multisig wallet?

Is my understanding multisig correct?

If you have coldcard, you know that there is a multisig menu in coldcard. So if creating multisig is simply inserting the coldcard’s xpub to electrum (where the multisig is going to be created) then I don’t need to care about the multisig menu on coldcard? Same with bluewallet, I don’t need to create a vault wallet in there?

Answer 1

There seems to be some variation in the question on wallet vs address. In any event a multisig address is simply a script created by m-of-n public keys (not addresses or wallets). When you build a raw multisig address in the bitcoin core console or with a software library really all you need are the public keys and specify how many are required to spend.

Can these public keys come from different single sig wallets? Of course, it could come from anywhere including different brain wallets (don't do this though, please just an example to prove a point) but as one commenter already noted taking non-standard approaches is a good way to lose your funds if you're not an advanced user.

It's best to stick with what most wallets support where you'll be using a new xpub created with your multisig wallet rather than your single sig xpubs.

Answer 2

My pre-understanding is that multisig wallet is simply a combination of many singlesig address. Is my understanding multisig correct?

Not exactly.
If we think of addresses as a locks a single-sig address is a lock that requires 1 key to unlock and a multi-sig address is a lock that requires multiple keys to unlock.
This "lock" is created using Bitcoin scripts and each address has a different type of script. So multi-sig is not "combination of single-sig addresses" but an entirely different script.
In a multi-sig script the evaluation requires from 0 to n signatures.

The problem with combining multiple wallet software is that since there is no universal way of implementing a wallet they usually don't behave the same.

• One problem is derivation path which xpubs don't contain and wallets usually don't let you change it either. This means importing an xpub from wallet A to wallet B could result in two entirely different child keys.
• Another problem I can think of is the order of public keys. Multi-sig [redeem] scripts look like m <pub1> <pub2> <pub3> n when this is hashed (to create the address) it will produce a different hash (and a different address) compared to m <pub2> <pub1> <pub3> n. This problem could be solved by lexicographic sorting but again wallet A may sort and wallet B may not.