@AccessesPartialKey
  private static HkdfPrfKey newKey(HkdfPrfParameters parameters, @Nullable Integer idRequirement)
      throws GeneralSecurityException {
    if (idRequirement != null) {
      throw new GeneralSecurityException("Id Requirement is not supported for HKDF PRF keys");
    }
    validate(parameters);
    return HkdfPrfKey.builder()
        .setParameters(parameters)
        .setKeyBytes(SecretBytes.randomBytes(parameters.getKeySizeBytes()))
        .build();
  }
This key manager generates new {@code HkdfPrfKey} keys and produces new instances of {@code
HkdfStreamingPrf} and {@code HkdfPrf}.
java_src/src/main/java/com/google/crypto/tink/prf/HkdfPrfKeyManager.java