return mac.Sum(make([]byte, 0, mac.Size())), nil
}

// parseCiphertext parses and converts a ciphertext into
// the format expected by a secretKey.
//
// Previous implementations of the secretKey produced a structured
// ciphertext. parseCiphertext converts all previously generated
// formats into the expected format.
func parseCiphertext(b []byte) ([]byte, kms.SecretKeyType) {
	if len(b) == 0 {
		return b, kms.AES256