ASP.NET C# code to PHP

Need to convert 1 C# IHttpHandler page into a PHP page, the total code involve is 120 lines main handler 350 lines utility class use by the handler The code involve use of the .NET [login to view URL] classes The code retrieve XML from external URL and use the data in the XML to validate incoming request. Request are encrypted and need to be decrypted and answer need to be encrypted. Attached the C# source code