Funny thing. I myself was looking for a more "secure" random number generator as "CL_ABAB_RANDOM".
My use case would be generating security codes for vouchers we issue from our system. While we take measures that we'd only accept vouchers that we actually issued ourselves, I, from an IT point of view would love to see a more "secure" implementation than above discussed built-in classes or FMs.
After some research I found this note http://service.sap.com/sap/support/notes/1410548 which mentions a kernel implemented "random number generator" that is touted to be secure and could be used to "secure communication".
The name of the FM is "GENERATE_SEC_RANDOM". Maybe this will suit your (and my) needs
Cheers
Jens