@AccessesPartialKey
  static HmacKey createNewHmacKey(HmacParameters parameters, @Nullable Integer idRequirement)
      throws GeneralSecurityException {
    return HmacKey.builder()
        .setParameters(parameters)
        .setKeyBytes(SecretBytes.randomBytes(parameters.getKeySizeBytes()))
        .setIdRequirement(idRequirement)
        .build();
  }
This key manager generates new {@code HmacKey} keys and produces new instances of {@code
PrfHmacJce}.
java_src/src/main/java/com/google/crypto/tink/mac/HmacKeyManager.java