An Analysis of Covert Timing Channels

Covert channels have tmditionally been categorized as either stomge channels or timing channels[6, 71. This paper questions this categorization, and discwses channels that cannot be clearly identified as either stomge or timing channels, but have aspects of both. A new model of timing channels is presented, which allows for channels that have chamcteristics of both stomge channels and timing channels, and a method is given for constructing all channels in a computer system that have timing channel chamcteristics. Since Kemmerer ’s shared n?aoume matriz methodology[5] has the potential to detect all channels that have storage chamcteristics, the two methods jointly have the capability to construct all channels in a computer system. The appmach to timing channels provides a jwtification of specific mechanisms for reducing their bandwidth which wen? employed in the VAX’ Virtual Machine Monitor, as described in [$] and [.].