@AccessesPartialKey
  private static AesGcmKey createAesGcmKey(
      AesGcmParameters parameters, @Nullable Integer idRequirement)
      throws GeneralSecurityException {
    validate(parameters);
    return AesGcmKey.builder()
        .setParameters(parameters)
        .setIdRequirement(idRequirement)
        .setKeyBytes(SecretBytes.randomBytes(parameters.getKeySizeBytes()))
        .build();
  }
This key manager generates new {@code AesGcmKey} keys and produces new instances of {@code
AesGcmJce}.
java_src/src/main/java/com/google/crypto/tink/aead/AesGcmKeyManager.java