private void initFromSpec(OAEPParameterSpec pSpec) throws NoSuchPaddingException {
    MGF1ParameterSpec mgfParams = (MGF1ParameterSpec) pSpec.getMGFParameters();
    Digest digest = JCEDigestUtil.getDigest(mgfParams.getDigestAlgorithm());

    if (digest == null) {
      throw new NoSuchPaddingException(
          "no match on OAEP constructor for digest algorithm: " + mgfParams.getDigestAlgorithm());
    }

    cipher =
        new OAEPEncoding(
            new RSABlindedEngine(), digest, ((PSource.PSpecified) pSpec.getPSource()).getValue());
    paramSpec = pSpec;
  }
  protected void engineInit(int opmode, Key key, AlgorithmParameterSpec params, SecureRandom random)
      throws InvalidKeyException, InvalidAlgorithmParameterException {
    CipherParameters param;

    if (params == null || params instanceof OAEPParameterSpec) {
      if (key instanceof RSAPublicKey) {
        if (privateKeyOnly) {
          throw new InvalidKeyException("mode 1 requires RSAPrivateKey");
        }

        param = RSAUtil.generatePublicKeyParameter((RSAPublicKey) key);
      } else if (key instanceof RSAPrivateKey) {
        if (publicKeyOnly) {
          throw new InvalidKeyException("mode 2 requires RSAPublicKey");
        }

        param = RSAUtil.generatePrivateKeyParameter((RSAPrivateKey) key);
      } else {
        throw new InvalidKeyException("unknown key type passed to RSA");
      }

      if (params != null) {
        OAEPParameterSpec spec = (OAEPParameterSpec) params;

        paramSpec = params;

        if (!spec.getMGFAlgorithm().equalsIgnoreCase("MGF1")
            && !spec.getMGFAlgorithm().equals(PKCSObjectIdentifiers.id_mgf1.getId())) {
          throw new InvalidAlgorithmParameterException(
              "unknown mask generation function specified");
        }

        if (!(spec.getMGFParameters() instanceof MGF1ParameterSpec)) {
          throw new InvalidAlgorithmParameterException("unkown MGF parameters");
        }

        Digest digest = JCEDigestUtil.getDigest(spec.getDigestAlgorithm());

        if (digest == null) {
          throw new InvalidAlgorithmParameterException(
              "no match on digest algorithm: " + spec.getDigestAlgorithm());
        }

        MGF1ParameterSpec mgfParams = (MGF1ParameterSpec) spec.getMGFParameters();
        Digest mgfDigest = JCEDigestUtil.getDigest(mgfParams.getDigestAlgorithm());

        if (mgfDigest == null) {
          throw new InvalidAlgorithmParameterException(
              "no match on MGF digest algorithm: " + mgfParams.getDigestAlgorithm());
        }

        cipher =
            new OAEPEncoding(
                new RSABlindedEngine(),
                digest,
                mgfDigest,
                ((PSource.PSpecified) spec.getPSource()).getValue());
      }
    } else {
      throw new IllegalArgumentException("unknown parameter type.");
    }

    if (!(cipher instanceof RSABlindedEngine)) {
      if (random != null) {
        param = new ParametersWithRandom(param, random);
      } else {
        param = new ParametersWithRandom(param, new SecureRandom());
      }
    }

    switch (opmode) {
      case Cipher.ENCRYPT_MODE:
      case Cipher.WRAP_MODE:
        cipher.init(true, param);
        break;
      case Cipher.DECRYPT_MODE:
      case Cipher.UNWRAP_MODE:
        cipher.init(false, param);
        break;
      default:
        throw new InvalidParameterException("unknown opmode " + opmode + " passed to RSA");
    }
  }