using System;

using System.Text;

using System.Security.Cryptography;

​

public class Program

{

    public static void Main()

    {

        var pwd = Encoding.UTF8.GetBytes("SomePwd");

        for (var input = 1; input < 1000000; input += 1000)

        {

            var enc = Convert.ToBase64String(RC4.Encrypt(pwd, BitConverter.GetBytes(input)));

​

            var dec = BitConverter.ToInt32(RC4.Decrypt(pwd, Convert.FromBase64String(enc)));

            Console.WriteLine($"{input}: {enc} is equal to {dec}");

        }

    }

}

​

public static class RC4

{

​

    public static byte[] Encrypt(byte[] pwd, byte[] data)

    {

        int a, i, j, k, tmp;

        int[] key, box;

        byte[] cipher;

​

        key = new int[256];

        box = new int[256];

        cipher = new byte[data.Length];

​

        for (i = 0; i < 256; i++)

        {

            key[i] = pwd[i % pwd.Length];

            box[i] = i;

        }

        for (j = i = 0; i < 256; i++)

        {

            j = (j + box[i] + key[i]) % 256;

            tmp = box[i];

            box[i] = box[j];

            box[j] = tmp;

        }

        for (a = j = i = 0; i < data.Length; i++)

        {

            a++;

            a %= 256;

            j += box[a];

            j %= 256;

            tmp = box[a];

            box[a] = box[j];

            box[j] = tmp;

            k = box[((box[a] + box[j]) % 256)];

            cipher[i] = (byte)(data[i] ^ k);

        }

        return cipher;

    }

​

    public static byte[] Decrypt(byte[] pwd, byte[] data)

    {

        return Encrypt(pwd, data);

    }

​

}