Secure Multi-Signature Transaction Management with Bitcoin.js
As a developer using Bitcoin.js, you’ve probably come across the need to manage transactions with multiple signatures. A multi-sig wallet (multiSig) allows multiple addresses to authorize and verify transactions on behalf of one address. In this article, we will look at how to create a secure and reliable multiSig setup in Bitcoin.js.
Problem: OP_CHECKSIGADD
When you use OP_CHECKSIGADD, it appends the signature of one or more signatures to the second public key. However, if there is only one valid signature, the transaction will likely be rejected by the network. To reduce this risk, we will use the second approach, using OP_CHECKSIG and OP_EQUAL with a threshold of 3-2.
Creating a Secure MultiSig Setup
To create a multiSig setup in Bitcoin.js, you need to perform the following steps:
- Create an account with a threshold of 3-2: Define the public key that will be used for the main account. This key must have at least three signatures, and at least two of them must be valid.
- Create a secondary account: Create another public key that will be used to authorize transactions on behalf of the primary account. This key must have at least 4 signatures (one signature is invalid).
- Generate Shared Secret: Use
OP_CHECKSIGto generate a shared secret between two accounts. This shared secret will contain all the necessary information for authorization.
- Verify the shared secret: Use
OP_EQUALwith the shared secret and one of the signatures of the secondary account to verify its validity.
Example Code
const Bitcoinjs = require('bitcoinjs-lib');
// Creating an account with threshold 3-2
const primaryAccountPubkey = 'xprv...';
const primarySigPubkey1 = 'xprv...'; // 3 signatures
const primarySigPubkey2 = 'xprv...'; // 2 signatures
const primarySigPubkey3 = 'xprv...'; // invalid signature
// Creating an additional account
const secondaryAccountPubkey = 'xprv...';
const secondarySigPubkey1 = 'xprv...'; // less than 4 signatures (one is invalid)
// Generation of a shared secret using OP_CHECKSIG and one of the signatures of the main account
async function generateSharedSecret() {
const sharedSecretPubkey = await Bitcoinjs.Secp256k1.createKeyPair(primaryAccountPubkey);
const signature1 = await Bitcoinjs.Secp256k1.sign(sharedSecretPubkey, primarySigPubkey1);
const signature2 = await Bitcoinjs.Secp256k1.sign(sharedSecretPubkey, primarySigPubkey2);
const signature3 = await Bitcoinjs.Secp256k1.sign(sharedSecretPubkey, primarySigPubkey3);
return { sharedSecret: JSON.stringify({ secret: sharedSecretPubkey, signatures: [signature1, signature2, signature3] }) };
}
// Check the shared secret using OP_EQUAL with one of the signatures of the secondary account
async function verifySharedSecret(sharedSecret) {
const { sharedSecret: { secret, signatures } } = JSON.parse(sharedSecret);
const signature = await Bitcoinjs.Secp256k1.sign(secret, secondarySigPubkey1);
return signature === signatures[0];
}
// Usage example:
generateSharedSecret().then(sharedSecret => {
verifySharedSecret(sharedSecret).then(verified => console.log(verified));
});
Best Practices
- Use a safe and reliable seed for the main account.
- Make sure all secondary accounts have less than 4 signatures (one is invalid).
- Keep the shared secret safe to prevent unauthorized access.
- Consider using a more reliable cryptographic library, such as
Bitcoinjs-secp256k1, which provides better security features.
By following these steps and best practices, you can securely manage multiSig transactions in your Bitcoin.js application. Remember to always handle confidential information with care and follow the recommendations of the Bitcoin community.