Noninvasive methods for host certification

Determining whether a user or system is exercising appropriate security practices is difficult in any context. Such difficulties are particularly pronounced when uncontrolled or unknown platforms join public networks. Commonly practiced techniques used to vet these hosts, such as system scans, have the potential to infringe on the privacy of users. In this article, we show that it is possible for clients to prove both the presence and proper functioning of security infrastructure without allowing unrestricted access to their system. We demonstrate this approach, specifically applied to antivirus security, by requiring clients seeking admission to a network to positively identify the presence or absence of malcode in a series of puzzles. The implementation of this mechanism and its application to real networks are also explored. In so doing, we demonstrate that it is not necessary for an administrator to be invasive to determine whether a client implements required security practices.