Recently I've been working on a multisig paper wallet using the bitcoinjs library.
With any bitcoin wallet, the most important part is the safety of user's funds. Part of the design process included what user input can be provided, and how much information to provide back to the user. The more steps or parts to the process opens up the user to more chances to make mistakes.
The current layout I have is:
- User provides an input for m and n for the m-of-n (ie 2 of 3, 3 of 5, etc)
- CSPRNG provided by bitcoinjs-lib creates n key pairs, and those public keys are used to create the multisig P2SH address.
- Output to user is the P2SH address on the left-hand side, and on the right-hand side the first private key out of n keys.
- The additional private keys can be cycled through using the arrow buttons above the private key QR code
- Additional output to the user includes the public keys (and qr codes) and the sequence they were used to create the address and redeem script.
- User can save redeem script hex to a USB drive, OR if they want to stay true to paper wallet regenerate the redeem script using the public key qr codes along with the `redeem-script.html` tool which can scan your public key qr codes with your webcam. Typing in by hand I suppose is a possible third option, but not likely or recommended considering the redeem script can be quite long.
To make the paper wallet more like a wallet, I have also added some additional standalone pages (tools) that will allow users to find UTXOs for specific addresses to build and sign transactions.
- Users build transactions with UTXO selection using the `multisig-build.html` tool. (internet needed to fetch UTXOs)
- Users sign transactions offline using the `multisig-sign.html` tool
- Users are responsible for broadcasting the raw hex transactions
Drawbacks I am noticing:
- building a transaction might be too advanced for some users
- fees should be satoshis per byte like segwitaddress.org instead of inputting exact fee in satoshis
- users cant create an address from their own provided public keys (yet, will add in the future)
- you tell me, what do you all think?
Here's the github repo:
https://github.com/coinables/MultiSigAddressand the domain I'm using:
https://multisigaddress.org?testnet=true
It currently supports both testnet and mainnet. I recommend users stick with testnet unless they really know what they are doing.
Some nuances with creating a multisig wallet is there are multiple ways it could be implemented, whereas a standard single key address is just a private key and address. One of the challenges is the redeem script can be too long for a QR code. I was thinking maybe multiple QR codes, but that got ugly quick, so instead I went with displaying the public keys QR codes and printed out the redeem script, giving users multiple options. This is the way I have decided to go, at least for a first attempt. Looking for thoughts, input, etc from others.
