encryption decryption in asp.net with c#

protected void Page_Load(object sender, EventArgs e)
   {
       InitializeComponent();
   }

   protected void Button1_Click(object sender, EventArgs e)
   {
       byte[] buffer = Encryption(textBox1.Text, txtKey.Text);
       string b = Convert.ToBase64String(buffer);
       textBox1.Text = b;
   }
   public static byte[] Encryption(string PlainText, string key)
   {
       TripleDES des = CreateDES(key);
       ICryptoTransform ct = des.CreateEncryptor();
       byte[] input = Encoding.Unicode.GetBytes(PlainText);
       return ct.TransformFinalBlock(input, 0, input.Length);
   }
   public static string Decryption(string CypherText, string key)
   {
       byte[] b = Convert.FromBase64String(CypherText);
       TripleDES des = CreateDES(key);
       ICryptoTransform ct = des.CreateDecryptor();
       byte[] output = ct.TransformFinalBlock(b, 0, b.Length);
       return Encoding.Unicode.GetString(output);
   }
   static TripleDES CreateDES(string key)
   {
       MD5 md5 = new MD5CryptoServiceProvider();
       TripleDES des = new TripleDESCryptoServiceProvider();
       des.Key = md5.ComputeHash(Encoding.Unicode.GetBytes(key));
       des.IV = new byte[des.BlockSize / 8];
       return des;
   }
   protected void Button2_Click(object sender, EventArgs e)
   {
       textBox2.Text = Decryption(textBox1.Text, txtKey.Text);
       //textBox3.Text = Decryption(textBox2.Text, txtKey.Text);
   }