code: function hash256(data) {
    const out = Buffer.allocUnsafe(32);
    ctx.init();
    ctx.update(data);
    ctx._finish(out);
    ctx.init();
    ctx.update(out);
    ctx._finish(out);
    return out;
  }
docs: Hash buffer with double sha256.
  @alias module:crypto/sha256.hash256
  @param {Buffer} data
  @returns {Buffer}