private static StreamingPrf createStreamingPrf(HkdfPrfKey key) throws GeneralSecurityException {
    validate(key.getParameters());
    return HkdfStreamingPrf.create(key);
  }
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