code: function secondSign (transaction, keys) {
  	var hash = getHash(transaction);
  	var signature = naclInstance.crypto_sign_detached(hash, Buffer.from(keys.privateKey, 'hex'));
  	transaction.signSignature = Buffer.from(signature).toString('hex');
  }
docs: @method secondSign
  @param transaction Object
  @param keys Object
  
  @return {string}