ninjaneo

using System;

namespace ninjacrypt
{
    class Program
    {
        static void Main(string[] args)
        {
            RC4 rc4;
            while(true)
            {
                try
                {
                    Console.Write("Key: ");
                    rc4 = new RC4(Console.ReadLine());
                    Console.Write("Message: ");
                    rc4.HexDump(rc4.Encrypt(Console.ReadLine()));
                }
                catch (RC4.NullKey)
                {
                    break;
                }
            }
        }
    }
    class RC4
    {
        private byte i, j;
        public byte[] state = new byte[256];
        public char[] key;

        public class NullKey : Exception
        {
        }

        void swap<T>(ref T i, ref T j)
        {
            T temp;
            temp = i;
            i = j;
            j = temp;
        }

        public RC4(string Key)
        {
            if (Key.Length == 0)
                throw new NullKey();
            key = Key.ToCharArray();
            // Generate the IV for the stream cipher
            for (i = 1;i != 0;++i)
                state[i] = i;
            j = (byte) key[0];
            swap(ref state[0],ref state[j]);
            for (i = 1; i != 0; ++i)
            {
                j += (byte) (state[i] + (byte)key[i % key.Length]);
                swap(ref state[i],ref state[j]);
            }
            i = 0;
            j = 0;
        }

        byte keybyte
        {
            get {
                ++i;
                j += state[i];
                swap(ref state[i],ref state[j]);
                return state[(state[i] + state[j]) & 255];
            }
        }

        public string Encrypt(string plaintext)
        {
            string cyphertext = "";
            foreach (byte m in plaintext)
                cyphertext += (char)(m ^ keybyte);
            return cyphertext;
        }

        public void HexDump(string str)
        {
            foreach (byte c in str)
            {
                Console.Write("{0:X2} ", c);
            }
            Console.Write("\n{0}\n",str);
        }
    }
}