Org.BouncyCastle.Crypto.Signers.ECGost3410Signer.GenerateSignature C# (CSharp) Method

        public BigInteger[] GenerateSignature(
            byte[] message)
        {
            byte[] mRev = new byte[message.Length]; // conversion is little-endian
            for (int i = 0; i != mRev.Length; i++)
            {
                mRev[i] = message[mRev.Length - 1 - i];
            }

            BigInteger e = new BigInteger(1, mRev);
            BigInteger n = key.Parameters.N;

            BigInteger r = null;
            BigInteger s = null;

            do // generate s
            {
                BigInteger k = null;

                do // generate r
                {
                    do
                    {
                        k = new BigInteger(n.BitLength, random);
                    }
                    while (k.SignValue == 0);

                    ECPoint p = key.Parameters.G.Multiply(k);

                    BigInteger x = p.X.ToBigInteger();

                    r = x.Mod(n);
                }
                while (r.SignValue == 0);

                BigInteger d = ((ECPrivateKeyParameters)key).D;

                s = (k.Multiply(e)).Add(d.Multiply(r)).Mod(n);
            }
            while (s.SignValue == 0);

            return new BigInteger[]{ r, s };
        }

        /**
         * Test Sign and Verify with A parameters
         * see: http://www.ietf.org/internet-drafts/draft-popov-cryptopro-cpalgs-01.txt
         * gostR3410-2001-CryptoPro-A-ParamSet  P.47
         */
        public void ecGOST3410_AParam()
        {
            SecureRandom    random = new SecureRandom();

            BigInteger mod_p = new BigInteger("115792089237316195423570985008687907853269984665640564039457584007913129639319"); //p

            FpCurve curve = new FpCurve(
                mod_p, // p
                new BigInteger("115792089237316195423570985008687907853269984665640564039457584007913129639316"), // a
                new BigInteger("166")); // b

            ECDomainParameters parameters = new ECDomainParameters(
                curve,
                new FpPoint(curve,
                new FpFieldElement(mod_p, new BigInteger("1")), // x
                new FpFieldElement(mod_p, new BigInteger("64033881142927202683649881450433473985931760268884941288852745803908878638612"))), // y
                new BigInteger("115792089237316195423570985008687907853073762908499243225378155805079068850323")); // q

            ECKeyPairGenerator pGen = new ECKeyPairGenerator("ECGOST3410");
            ECKeyGenerationParameters genParam = new ECKeyGenerationParameters(
                parameters,
                random);

            pGen.Init(genParam);

            AsymmetricCipherKeyPair  pair = pGen.GenerateKeyPair();

            ParametersWithRandom param = new ParametersWithRandom(pair.Private, random);

            ECGost3410Signer ecgost3410 = new ECGost3410Signer();

            ecgost3410.Init(true, param);

            BigInteger[] sig = ecgost3410.GenerateSignature(hashmessage);

            ecgost3410.Init(false, pair.Public);

            if (!ecgost3410.VerifySignature(hashmessage, sig[0], sig[1]))
            {
                Fail("signature fails");
            }
        }