Abstract
We analyze the DEC fuzzy time technique (Hu [HU]) for both a single computer system and a network of hosts. Specifically, we investigate 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 bits per second, given a mean time between upticks of 20 milliseconds as in the VAX security kernel. We suggest several countermeasures including scheduler redesign which will close or reduce the channels that we analyze.
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