B2,3 and A1 system (Orange book), use covert channel analysis to prevent leakages of information (intentional or otherwise). This forms a part of enforcing MAC on such systems. well recently i thought of a method to overcome these barriers so covert channels can again be used to transmit and receive from such machines. this method involves using quantum cryptography. "randomization" is one method used to prevent covert channels, however it is this "randomization" that can be used with quantum crypto to not only make covert channels, but also makes the covert channels secure as well as authenticated! basically quantum crypto uses the fact that observing a system modifies the system. this works on machines that use "randomization" as a method of detering covert channels. ObExample, if an admin gets suspicious of certain behaviour on a machine, the machine behaves differently if he tries to investigate it (as a result of "poking around" the machine to see what is going on). this can be used with quatum crypto methods to covertly communicate data (with security and authentification), and if someone attempts to "observe" the behaviour on the said machines, it will break the communication (because the machine behaviour changes, hence breaks the message) rendering the message unreadable. this may slow down communication some, and will need self-synchronization of some sort, but at least you can communicate. this idea is very rough however, and there may be gaping holes in my arguments, but i think it might be an area someone may wish to look into (especially the high assurance types). i really should write a draft paper on this, but i dont really have a good enough understanding of the formal methods to pull it off. however i have got a coining name for this method, "covert quantum channels". just a random thought to throw around... Matt -- #!/bin/sh echo '16i[q]sa[ln0=aln100%Pln100/snlbx]sbA0D3F204445524F42snlbxq'|dc;exit Matthew Keenan Systems Programmer Information Technology Division University of Technology Sydney Australia It's nice to be in a position where people apologize because they assume there's humor in your work, based on past experience, but they're not sure where it is. -- Rob Pike