XML : How to sign an xml document with private key in .key format and .crt certificate in C# with BouncyCastle?

I need sign an XML document in C# with BouncyCastle. This in openssl format, do as follows:

  openssl smime -sign -signer certificado.crt -inkey clave -out LoginTicketRequest.xml.cms -in LoginTicketRequest.xml -outform PEM -nodetach    

I need generate a file extension .cms with C#, but i dont know how do it. Because i have two files a CRT and key. Very thank you for read my post! :-)