@Override
    public void verifyMac(byte[] mac, byte[] data) throws GeneralSecurityException {
      if (!Bytes.equal(computeMac(data), mac)) {
        throw new GeneralSecurityException("invalid MAC");
      }
    }
@param serializedKeyFormat serialized {@code HmacKeyFormat} proto
@return {@code KeyData} with a new {@code HmacKey} proto
java_src/src/main/java/com/google/crypto/tink/mac/internal/LegacyHmacTestKeyManager.java