private static Prf createPrf(HkdfPrfKey key) throws GeneralSecurityException {
    return PrfImpl.wrap(createStreamingPrf(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