Modelling a fuzzy time system

The author gives an analysis of the fuzzy time covert channel reduction technique developed at the Digital Equipment Corporation (DEC) and applied to the VAX security kernel for both a single computer system and a network of hosts. Specifically, he investigates covert channels in a model of a fuzzy time system and in a network model of n fuzzy time hosts and one nonfuzzy time host. The fuzzy time operating system model predicts a covert channel with a datarate of roughly 50 b/s, given a mean time between upticks of 20 ms as in the VAX security kernel. Several countermeasures including scheduler redesign are suggested, which will close or reduce the channels that are analyzed.<
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