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;
    }

}