@Override
  public HpkeKemEncapOutput authEncapsulate(
      byte[] recipientPublicKey, HpkeKemPrivateKey senderPrivateKey)
      throws GeneralSecurityException {
    return authEncapsulate(recipientPublicKey, X25519.generatePrivateKey(), senderPrivateKey);
  }
Helper function factored out to facilitate unit testing.
java_src/src/main/java/com/google/crypto/tink/hybrid/internal/X25519HpkeKem.java