Encrypt and decrypt

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Threading;
using System.IO;
using System.Diagnostics;
using System.Security.Cryptography;

namespace MMT
{
    public class Encryptdata
    {

//ENCRYPT THE PASSWORD KEY(OPEN,EDIT)


        public static string Encrypt(string originalString)
        {
            if (String.IsNullOrEmpty(originalString))
            {
                originalString = "NO";
                //throw new ArgumentNullException("The string which needs to be encrypted can not be null.");
            }

            DESCryptoServiceProvider cryptoProvider = new DESCryptoServiceProvider();
            MemoryStream memoryStream = new MemoryStream();
            CryptoStream cryptoStream = new CryptoStream(memoryStream, cryptoProvider.CreateEncryptor(bytes, bytes), CryptoStreamMode.Write);

            StreamWriter writer = new StreamWriter(cryptoStream);
            writer.Write(originalString);
            writer.Flush();
            cryptoStream.FlushFinalBlock();
            writer.Flush();

            return Convert.ToBase64String(memoryStream.GetBuffer(), 0, (int)memoryStream.Length);
        }
   



        static byte[] bytes = ASCIIEncoding.ASCII.GetBytes("ZeroCool");

        public static string Decrypt(string cryptedString)
        {
            if (String.IsNullOrEmpty(cryptedString))
            {
                cryptedString = "NO";
                cryptedString = Encrypt(cryptedString);
                //throw new ArgumentNullException("The string which needs to be decrypted can not be null.");
           }

            DESCryptoServiceProvider cryptoProvider = new DESCryptoServiceProvider();
            MemoryStream memoryStream = new MemoryStream(Convert.FromBase64String(cryptedString));
            CryptoStream cryptoStream = new CryptoStream(memoryStream, cryptoProvider.CreateDecryptor(bytes, bytes), CryptoStreamMode.Read);
            StreamReader reader = new StreamReader(cryptoStream);

            return reader.ReadToEnd();
        }
     } 

}