Can not set our p and q values manually in RSA algorithm

See more:

C#

encryption

RSA

I have the C# code that does encryption with RSA algorithm but I want to give my own p and q, when I try to give for instance; p=11 q=5 manually. When I try to set my values manually inside Create() method, it gives me error at ModInverse() saying System.ArgumentException: 'a is not convertible.'

What I have tried:

public void RSACompatibility()
        {
            var rsa = new RSACryptoServiceProvider(512);
            var parameters = rsa.ExportParameters(true);

            var recreatedParameters = Create(parameters.P, parameters.Q, parameters.Exponent, parameters.Modulus);
            var recreatedRSA = new RSACryptoServiceProvider();
            recreatedRSA.ImportParameters(recreatedParameters);

            byte[] message = Encoding.UTF8.GetBytes("hello");
            var ciphertext = rsa.Encrypt(message, false);
            var plaintext = recreatedRSA.Decrypt(ciphertext, false);
            string recreatedMessage = Encoding.UTF8.GetString(plaintext);

            var bw = new BinaryWriter(File.Open("path", FileMode.OpenOrCreate));
            bw.Write(ciphertext);
        }

        private static RSAParameters Create(byte[] p, byte[] q, byte[] exponent, byte[] modulus)
        {
            //set number to byte array
            int intValueP = 51;
            int intValueQ = 7;
            byte[] intBytes = BitConverter.GetBytes(intValueP);
            byte[] intBytes2 = BitConverter.GetBytes(intValueQ);
            var addlParameters = GetFullPrivateParameters(
                p: new BigInteger(CopyAndReverse(intBytes)),
                q: new BigInteger(CopyAndReverse(intBytes2)),
                e: new BigInteger(CopyAndReverse(exponent)),
                modulus: new BigInteger(CopyAndReverse(modulus)));

            return new RSAParameters
            {
                P = p,
                Q = q,
                Exponent = exponent,
                Modulus = modulus,
                D = addlParameters.D,
                DP = addlParameters.DP,
                DQ = addlParameters.DQ,
                InverseQ = addlParameters.InverseQ,
            };
        }

        private static RSAParameters GetFullPrivateParameters(BigInteger p, BigInteger q, BigInteger e, BigInteger modulus)
        {
            
            var n = p * q;
            var phiOfN = n - p - q + 1; // OR: (p - 1) * (q - 1);

            var d = ModInverse(e, phiOfN);
            

            var dp = d % (p - 1);
            var dq = d % (q - 1);

            var qInv = ModInverse(q, p);
          

            return new RSAParameters
            {
                D = CopyAndReverse(d.ToByteArray()),
                DP = CopyAndReverse(dp.ToByteArray()),
                DQ = CopyAndReverse(dq.ToByteArray()),
                InverseQ = CopyAndReverse(qInv.ToByteArray()),
            };
        }

        private static BigInteger Encrypt(BigInteger m, BigInteger n, BigInteger e)
        {
            return BigInteger.ModPow(m, e, n);
        }

        private static BigInteger Decrypt(BigInteger mEnc, BigInteger d, BigInteger n)
        {
            return BigInteger.ModPow(mEnc, d, n);
        }


        public static BigInteger ModInverse(BigInteger a, BigInteger n)
        {
            BigInteger t = 0, nt = 1, r = n, nr = a;

            if (n < 0)
            {
                n = -n;
            }

            if (a < 0)
            {
                a = n - (-a % n);
            }

            while (nr != 0)
            {
                var quot = r / nr;

                var tmp = nt; nt = t - quot * nt; t = tmp;
                tmp = nr; nr = r - quot * nr; r = tmp;
            }

            if (r > 1) throw new ArgumentException(nameof(a) + " is not convertible.");
            if (t < 0) t = t + n;
            return t;
        }

        private static byte[] CopyAndReverse(byte[] data)
        {
            byte[] reversed = new byte[data.Length];
            Array.Copy(data, 0, reversed, 0, data.Length);
            Array.Reverse(reversed);
            return reversed;
        }