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);
}