code: public static byte[] decryptSimple(BigInteger privKey, byte[] cipher) throws IOException, InvalidCipherTextException {
          ArxanIESEngine iesEngine = new ArxanIESEngine(
                  new ECDHBasicAgreement(),
                  new MGF1BytesGeneratorExt(new SHA1Digest(), 1),
                  new HMac(new SHA1Digest()),
                  new SHA1Digest(),
                  null);
  
          IESParameters p = new IESParameters(null, null, KEY_SIZE);
          ParametersWithIV parametersWithIV = new ParametersWithIV(p, new byte[0]);
  
          iesEngine.setHashMacKey(false);
  
          iesEngine.init(new ECPrivateKeyParameters(privKey, CURVE), parametersWithIV,
                  new ECIESPublicKeyParser(ECKey.CURVE));
  
          return iesEngine.processBlock(cipher, 0, cipher.length);
      }
docs: Encryption equivalent to the Crypto++ default ECIES ECP settings:
  
  DL_KeyAgreementAlgorithm:        DL_KeyAgreementAlgorithm_DH struct ECPPoint,struct EnumToType enum CofactorMultiplicationOption,0
  DL_KeyDerivationAlgorithm:       DL_KeyDerivationAlgorithm_P1363 struct ECPPoint,0,class P1363_KDF2 class SHA1
  DL_SymmetricEncryptionAlgorithm: DL_EncryptionAlgorithm_Xor class HMAC class SHA1 ,0
  DL_PrivateKey:                   DL_Key ECPPoint
  DL_PrivateKey_EC class ECP
  
  Used for Whisper V3
  
  @param privKey privKey
  @param cipher cipher
  @return decryptSimple byte[] data
  @throws IOException IOException
  @throws InvalidCipherTextException InvalidCipherTextException