@AccessesPartialKey
  private static com.google.crypto.tink.hybrid.HpkePrivateKey parsePrivateKey(
      HpkePrivateKey protoKey) throws GeneralSecurityException {
    HpkePublicKey publicKey = LegacyHybridEncryptKeyManager.parsePublicKey(protoKey.getPublicKey());
    return com.google.crypto.tink.hybrid.HpkePrivateKey.create(
        publicKey,
        SecretBytes.copyFrom(
            protoKey.getPrivateKey().toByteArray(), InsecureSecretKeyAccess.get()));
  }
A KeyManager for HybridDecrypt with a custom type URL for testing.
java_src/src/main/java/com/google/crypto/tink/hybrid/internal/testing/LegacyHybridDecryptKeyManager.java