public static byte[] decryptSimple(BigInteger privKey, byte[] cipher) throws InvalidCipherTextException {
EthereumIESEngine iesEngine = new EthereumIESEngine(
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);
}