You are mixing concepts:
1- Data protection: can be done using encryption, digital signature, or combination of both.
2- Data transport: Can be done using secure transport protocols, such HTTPS, FTPS and SFTP.
AS2 protocol does not deal with transport by itselves, is a message exchange definition [url]http://en.wikipedia.org/wiki/AS2[/url] (No idea if supported by wM).
For transport side, IS does support HTTPS and FTPS out of the box, but not SFTP. However I saw some implementations for SFTP in the samples area using a OpenSource framework.
I would say TN gives you already all the needed protection in both areas, data security and transport. Maybe take a look at TN Administrators guide.
Hope this helps 