code: func ComputeTxID(nonce, creator []byte) (string, error) {
  	// TODO: Get the Hash function to be used from
  	// channel configuration
  	digest, err := factory.GetDefault().Hash(
  		append(nonce, creator...),
  		&bccsp.SHA256Opts{})
  	if err != nil {
  		return "", err
  	}
  	return hex.EncodeToString(digest), nil
  }
docs: // ComputeTxID computes TxID as the Hash computed
  // over the concatenation of nonce and creator.