Des encryption, C#

Des encryption

//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Security.Cryptography;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {
            var data = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 };
                var key = new byte[] { 01, 12, 23, 34, 45, 56, 67, 78, 89, 90, 09, 98, 87, 76, 65, 54, 43, 32, 21, 10, 11, 22, 33, 44 };
                var encrypted = Encrypt(data, key, 0);
                Console.WriteLine(encrypted);
                var decrypted = Decrypt(encrypted, key, 0);
                // decrypted should be equal to data here
        }
        
        public static string Encrypt(byte[] data, byte[] key, long nonce)
        {
            return Convert.ToBase64String(Transform(data, key, nonce));
        }
        
        public static byte[] Decrypt(string data, byte[] key, long nonce)
        {
            return Transform(Convert.FromBase64String(data), key, nonce);
        }
        
        static byte[] Transform(byte[] data, byte[] key, long nonce)
        {
            if (data.Length > 96/8) throw new ArgumentException("Too much data");
        
            using (var des = new TripleDESCryptoServiceProvider())
            {
                des.Key = key;
                des.Mode = CipherMode.ECB;
                using (var encryptor = des.CreateEncryptor())
                {
                    var output = new byte[data.Length];
                    var offset = 0;
                    for(int counter = 0; counter <= data.Length / 8; ++counter)
                    {
                        var counterData = BitConverter.GetBytes(((long)counter) ^ nonce);
                        var counterEncryption = new byte[des.BlockSize / 8];
                        var counterEncryptionLen = encryptor.TransformBlock(counterData, 0, counterData.Length, counterEncryption, 0);
                        //Debug.Assert(counterEncryptionLen == counterEncryption.Length);
                        for (var i = 0; i < des.BlockSize / 8 && offset < output.Length; ++i, ++offset)
                        {
                            output[offset] = (byte)(data[offset] ^ counterEncryption[i]);
                        }
                    }
                    return output;
                }
            }
        }        
    }
}


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