#Csharp: #RC 4 + Base64

using System.IO;
using System;
using System.Text;

class Program
{
    static void Main()
    {
        String input = "data của anh nè";
        String key = "aaa";
        String encryptedStr = Program.Encrypt(input, key);
        String decryptedStr = Program.Decrypt(encryptedStr, key);
        Console.WriteLine("Input string: {0} \nKey: {1}", input, key);
        Console.WriteLine("Encrypted: {0}\nDecrypted: {1}", encryptedStr, decryptedStr);
    }

    static string Encrypt(string input, string key){
        byte[] plainTextBytes = System.Text.Encoding.UTF8.GetBytes(input);
        byte[] encrypted = RC4(plainTextBytes, key);
        return System.Convert.ToBase64String(encrypted);
    }

    static string Decrypt(string input, string key){
        byte[] base64EncodedBytes = System.Convert.FromBase64String(input);
        byte[] bin = RC4(base64EncodedBytes, key);
        return System.Text.Encoding.UTF8.GetString(bin);
    }

    public static byte[] RC4(byte[] data, string pwdKey) {
        int a, i, j, k, tmp;
        int[] key, box;
        byte[] cipher;

        key = new int[256];
        box = new int[256];
        cipher = new byte[data.Length];
        byte[] pwd = System.Text.Encoding.UTF8.GetBytes(pwdKey);

        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;
    }

}