how to encode/decode plain text in .net.

 [Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.ReadWrite)]
        public string encodetext(string plaintext)
        {
            return WebUtility.HtmlEncode(plaintext);
        }

 
    [Ajax.AjaxMethod(Ajax.HttpSessionStateRequirement.ReadWrite)]
        public string decodetext(string encodedtext)
        {
            return WebUtility.HtmlDecode(encodedtext);
        }