@AccessesPartialKey
  private static AesCmacKey createAesCmacKey(
      AesCmacParameters parameters, @Nullable Integer idRequirement)
      throws GeneralSecurityException {
    validateParameters(parameters);
    return AesCmacKey.builder()
        .setParameters(parameters)
        .setAesKeyBytes(SecretBytes.randomBytes(parameters.getKeySizeBytes()))
        .setIdRequirement(idRequirement)
        .build();
  }
This key manager generates new {@code AesCmacKey} keys and produces new instances of {@code
AesCmac}.
java_src/src/main/java/com/google/crypto/tink/mac/AesCmacKeyManager.java