[IS] MH cryptosystem

using System;
using System.Text;

namespace Lab2
{
    class Program
    {
        const int size = 5;
        static void Main(string[] args)
        {
            int m, t;
            int[] key = new int[size], enkey = new int[size];
            string iobuff;
            string[] arrkey = new string[size];
            m = 63; t = 29;
            key = new int[size] {2, 3, 6, 13, 27};
            //input key information
            /*
            Console.Write("Input m: ");
            m = int.Parse(Console.ReadLine());

            Console.Write("Input t: ");
            t = int.Parse(Console.ReadLine());

            Console.Write("Input key: ");
            iobuff = Console.ReadLine();
            arrkey = iobuff.Split(' ');
            for (int i = 0; i < arrkey.Length; i++)
            {
                key[i] = int.Parse(arrkey[i]);
            }*/

            //generate key for encryption
            enkey = genKey(m, t, key);
            Console.Write("Secret key: ");
            foreach (int n in enkey)
            {
                Console.Write("{0} ", n);
            }
            Console.WriteLine();

            //encrypt
            Console.WriteLine("Input string: ");
            iobuff = Console.ReadLine();
            Console.WriteLine("Encrypted string: {0}", genMt(m, t));

            int[] cryp = encrypt(iobuff, enkey);

            //gen decrypt key and decrypt
            enkey = genKey(m, genMt(m, t), enkey);
            foreach (int n in enkey)
            {
                Console.Write("{0} ", n);
            }
            Console.WriteLine();

            //Console.WriteLine("Input string: ");
            //iobuff = Console.ReadLine();
            Console.WriteLine("Encrypted string: {0}", decrypt(cryp, enkey, genMt(m, t), m));


            Console.ReadKey();
        }


        static int[] encrypt(string s, int[] key)
        {
            StringBuilder ctext = new StringBuilder(s);
            int[] crypted = new int[ctext.Length];

            for (int i = 0; i < ctext.Length; i++)
            {
                if (char.IsLetter(ctext[i]))
                {
                    int nc = 0;
                    bool upper = char.IsUpper(ctext[i]);
                    if (upper) ctext[i] = (char)(ctext[i] + 32);
                    string bin = numToBin(ctext[i] - 96);
                    for (int j = 0; j < bin.Length; j++)
                    {
                        nc += key[j] * (bin[j] - 48);
                    }
                    crypted[i] = nc;
                    if (upper) ctext[i] = (char)(ctext[i] - 32);
                }
                else if (ctext[i] == ' ') crypted[i] = 0;
            }

            return crypted;
        }

        static string decrypt(int[] crypted, int[] key, int mt, int m)
        {
            StringBuilder text = new StringBuilder(crypted.Length);
            for (int i = 0; i < crypted.Length; i++)
            {
                if (crypted[i] == 0)
                {
                    text.Append(' ');
                    continue;
                }
                    int nc = 0;
                    char[] bin = new char[size];
                    crypted[i] = (crypted[i]*mt) % m;
                    for (int j = key.Length-1; j >= 0; j--)
                    {
                        if (crypted[i] - key[j] >= 0)
                        {
                            crypted[i] -= key[j];
                            bin[j] = '1';
                        }
                        else { bin[j] = '0'; }
                    }
                    for (int k = 0; k < bin.Length; k++)
                        nc += (bin[k] - 48) * (int)Math.Pow(2, bin.Length - k -1);

                    text.Append((char)(nc % 27 + 96));

            }

            return text.ToString();
        }

        static int[] genKey(int m, int t, int[] key)
        {
            int[] outKey = new int[key.Length];
            for (int i = 0; i < key.Length; i++)
            {
                outKey[i] = (key[i]*t)%m;
            }
            return outKey;
        }

        static int genMt(int m, int t)
        {
            for (int i = 0; i < m; i++)
            {
                if ((t*i)%m == 1)
                {
                    return i;
                }
            }

            return -1;
        }

        static string numToBin(int num)
        {
            char[] bin = new char[size];
            int testNumber = 1;
            for (int i = size-1; i >= 0; i--)
            {
                bin[i] += (num & testNumber) > 0 ? '1' : '0';
                testNumber = testNumber << 1;
            }

            return new string(bin);
        }


        /*static string encrypt(string s , int[] key)
        {
            StringBuilder ctext = new StringBuilder(s);
            for (int i = 0; i < ctext.Length; i++)
            {
                if (char.IsLetter(ctext[i]))
                {
                    int nc = 0;
                    bool upper = char.IsUpper(ctext[i]);
                    if (upper) ctext[i] = (char)(ctext[i] + 32);
                    string bin = numToBin(ctext[i] - 96);
                    for (int j = 0; j < bin.Length; j++)
                    {
                        nc += key[j] * (bin[j] - 48);
                    }
                    ctext[i] = (char)(nc % 27 + 96);
                    if (upper) ctext[i] = (char)(ctext[i] - 32);
                }
            }

            return ctext.ToString();
        }*/


        /*
        static string decrypt(string s, int[] key, int mt)
        {
            StringBuilder text = new StringBuilder(s);
            for (int i = 0; i < text.Length; i++)
            {
                if (char.IsLetter(text[i]))
                {
                    int nc = 0;
                    bool upper = char.IsUpper(text[i]);
                    if (upper) text[i] = (char)(text[i] + 32);
                    string bin = numToBin((text[i] - 96) * mt);
                    for (int j = 0; j < bin.Length; j++)
                    {
                        nc += key[j] * (bin[j] - 48);
                    }
                    text[i] = (char)(nc % 27 + 96);
                    if (upper) text[i] = (char)(text[i] - 32);
                }
            }

            return text.ToString();
        }*/
    }
}