using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            Byte[] Key = new Byte[256];
            Byte[] Content = new Byte[256];
            string line = "";
            int stringDlzka = 0;
            int keyDlzka = 0;

            Console.Write(" Zadaj string:\n ");
            line = Console.ReadLine();
            int index = 0;
            // pre kazdy (ASCII hodnota) znak v zadanom stringu
            foreach (int c in line)
            {
             // max 256 znakov; znak je A     -    Z  alebo   a     -     z  alebo medzera
                if (index < 256 && c >= 65 && c <= 90 || c >= 97 && c <= 122 || c == 32)
                {
                    Content[index] = (Byte)c;
                    index++;
                }
            }
            stringDlzka = index;

            Console.Write(" Zadaj kluc:\n ");
            line = Console.ReadLine();
            index = 0;
            // pre kazdy (ASCII hodnota) znak v zadanom stringu
            foreach (int c in line)
            {
                // max 256 znakov; znak je A     -    Z  alebo   a     -     z
                if (index < 256 && c >= 65 && c <= 90 || c >= 97 && c <= 122)
                {
                    Key[index] = (Byte)c;
                    index++;
                }
            }
            keyDlzka = index;

            // encrypt
            RC4(ref Content, Key, stringDlzka, keyDlzka);
            Console.Write(" Encrytped:\n ");
            for (int i = 0; i < stringDlzka; i++)
                Console.Write((char)Content[i]);

            Console.WriteLine();
            Console.ReadKey(true);

            // decrypt
            RC4(ref Content, Key, stringDlzka, keyDlzka);
            Console.Write(" Decrytped:\n ");
            for (int i = 0; i < stringDlzka; i++)
                Console.Write((char)Content[i]);

            Console.Write("\n ");
            Console.ReadKey(true);
        }

        public static void RC4(ref Byte[] bytes, Byte[] key, int stringDlzka, int keyDlzka)
        {
            Byte[] s = new Byte[256];
            Byte[] k = new Byte[256];
            Byte temp;
            int i, j;

            for (i = 0; i < 256; i++)
            {
                s[i] = (Byte)i;
                k[i] = key[i % keyDlzka];
            }

            j = 0;
            for (i = 0; i < 256; i++)
            {
                j = (j + s[i] + k[i]) % 256;
                temp = s[i];
                s[i] = s[j];
                s[j] = temp;
            }

            i = j = 0;
            for (int x = 0; x < stringDlzka; x++)
            {
                i = (i + 1) % 256;
                j = (j + s[i]) % 256;
                temp = s[i];
                s[i] = s[j];
                s[j] = temp;
                int t = (s[i] + s[j]) % 256;
                bytes[x] ^= s[t];
            }
        }
    }
}