Managing the risk of covert information flows in virtual machine systems
Proceedings of the 12th ACM symposium on Access control models and technologies
An analysis of the timed Z-channel
SP'96 Proceedings of the 1996 IEEE conference on Security and privacy
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We analyze the DEC fuzzy time technique (Hu [2])for both a single computer system and a network ofhosts. Specifically, we investigate covert channels in amodel of a fuzzy time system and in a network modelof n fuzz y time hosts and one nonfuzzy time host. Thefuzzy time operating system model predicts a covertchannel with a datarate of roughly 50 bits per second,given a mean time between upticks of 20 millisecondsas in the VAX security kernel. We suggest several countermeasures including scheduler redesign which will close or reduce the channels that we analyze.