>I am wondering if there is any implemenation of the IPSec/IKE on the OSes >for handheld, e.g. Palm OS, WinCE. what could possibly be the constraints? nowadays you can run NetBSD (UNIX operating system) on WinCE devices, so there's no problem. you just need a right software :-) http://www.netbsd.org/Ports/hpcmips/ itojun