Encrypt .NET

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net.NetworkInformation;
using System.Security.Cryptography;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var plainTextBytes = Encrypt("0030Y00000S6EqWQAV");
            Console.WriteLine(plainTextBytes);
            Console.ReadKey();
        }

        public static string Encrypt(string originalString)
        {
            if (String.IsNullOrEmpty(originalString))
            {
                throw new ArgumentNullException
                       ("The string which needs to be encrypted can not be null.");
            }

            byte[] key = ASCIIEncoding.ASCII.GetBytes("12345678");
            DESCryptoServiceProvider cryptoProvider = new DESCryptoServiceProvider();
            cryptoProvider.Mode = CipherMode.ECB;
            cryptoProvider.Padding = PaddingMode.Zeros;
            MemoryStream memoryStream = new MemoryStream();
            CryptoStream cryptoStream = new CryptoStream(memoryStream,
                cryptoProvider.CreateEncryptor(key, key), CryptoStreamMode.Write);
            StreamWriter writer = new StreamWriter(cryptoStream);
            writer.Write(originalString);
            writer.Flush();
            cryptoStream.FlushFinalBlock();
            writer.Flush();
            var encryptedString = Convert.ToBase64String(memoryStream.GetBuffer(), 0, (int)memoryStream.Length);

            var plainTextBytes = Encoding.UTF8.GetBytes(encryptedString);

            return Convert.ToBase64String(plainTextBytes);
        }
    }
}