@cmdcode/musig2/dist/verify.js

Create digital signatures based on the Musig2 protocol.

import { Buff } from '@cmdcode/buff';
import { CONST } from '@cmdcode/crypto-tools';
import { pt } from '@cmdcode/crypto-tools/math';
import { get_key_coeff } from './pubkey.js';
import { combine_psigs } from './sign.js';
import { parse_psig } from './util.js';
import * as assert from './assert.js';
const { _G, _N } = CONST;
export function verify_psig(context, psig) {
    const { challenge, key_coeffs, nonce_coeff } = context;
    const { group_state, nonce_state } = context;
    const { sig, pubkey, nonces } = parse_psig(psig);
    assert.in_field(sig);
    const Q = group_state;
    const R = nonce_state;
    const kvec = get_key_coeff(pubkey, key_coeffs);
    const P = pt.lift_x(pubkey);
    const g_P = (Q.parity * Q.state) % _N;
    const coef = (challenge.big * kvec.big * g_P) % _N;
    const R_s1 = pt.lift_x(nonces[0]);
    const R_s2 = pt.lift_x(nonces[1]);
    const R_sP = pt.add(R_s1, pt.mul(R_s2, nonce_coeff));
    const R_s = pt.mul(R_sP, R.parity);
    assert.valid_point(R_s);
    const S1 = pt.gen(sig);
    const S2 = pt.add(R_s, pt.mul(P, coef));
    assert.valid_point(S1);
    assert.valid_point(S2);
    return pt.to_bytes(S1).hex === pt.to_bytes(S2).hex;
}
export function verify_musig(context, signature) {
    const { challenge, group_pubkey } = context;
    const sig = (Array.isArray(signature))
        ? combine_psigs(context, signature)
        : signature;
    const [rx, s] = Buff.parse(sig, 32, 64);
    const S = pt.mul(_G, s.big);
    const R = pt.lift_x(rx, true);
    const P = pt.lift_x(group_pubkey, true);
    const c = Buff.bytes(challenge).big;
    const SP = pt.add(R, pt.mul(P, c));
    assert.valid_point(S);
    return pt.eq(S, SP);
}
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