Hi
To secure your SAPGUI communication you can use SNC Client Encryption 1.0.
It's based on Microsoft Kerberos technology and should be available for download without additional licenses.
Simple solution
- computer/user with account in Microsoft AD
- export kerberos keys for NW server
- configure client and server for SNC kerberos
1643878 - Release Notes for SNC Client Encryption.
If you want to use SSO scenarios or certificates you need licenses for product:
SAP NetWeaver Single Sign-On
1912175 - SAP Single Sign-On 2.0: Central Note
The are 3rd party solutions too.
Regards
Przemek