bls.js

const bls = require('bls-lib');

bls.onModuleInit(() => {
    bls.init();
    const numOfPlayers = 7;
    const threshold = 3;
    const msg = 'hello world';
    console.log({numOfPlayers, threshold, msg});

    // set up master key share
    const masterSecretKey = [];
    const masterPublicKey = [];
    for (let i = 0; i < threshold; i++) {
        const sk = bls.secretKey();
        bls.secretKeySetByCSPRNG(sk);
        masterSecretKey.push(sk);

        const pk = bls.publicKey();
        bls.getPublicKey(pk, sk);

        masterPublicKey.push(pk);
    }

    // key sharing
    const ids = [];
    const secretKeys = [];
    console.log('secret key shares:');
    for (let i = 0; i < numOfPlayers; i++) {
        const id = bls.secretKey();
        bls.secretKeySetByCSPRNG(id);
        ids.push(id);

        const sk = bls.secretKey();
        bls.secretKeyShare(sk, masterSecretKey, id);
        secretKeys.push(sk);
        console.log(`${Buffer.from(bls.secretKeyExport(id)).toString('hex')}: ${Buffer.from(bls.secretKeyExport(sk)).toString('hex')}`);
    }

    // signing
    const subIds = [];
    const subSigs = [];
    console.log('signatures:');
    for (let i = 0; i < threshold; i++) {
        const id = numOfPlayers - i - 1;
        subIds.push(ids[id]);
        const sk = secretKeys[id];
        const sig = bls.signature();
        bls.sign(sig, sk, msg);
        subSigs.push(sig);
        console.log(`${Buffer.from(bls.secretKeyExport(ids[id])).toString('hex')}: ${Buffer.from(bls.signatureExport(sig)).toString('hex')}`);
    }

    // verify
    const sig = bls.signature();
    bls.signatureRecover(sig, subSigs, subIds);
    const result = bls.verify(sig, masterPublicKey[0], msg);
    console.log({verified: result});
});