An Analysis of Covert Timing Channels

Abstract

Covert channels have traditionally been categorized as either storage channels or timing channels [8, 9]. This paper questions this categorization, and discusses channels that cannot be clearly identified as either storage or timing channels, but have aspects of both.

A new model of timing channels is presented, which allows for channels that have characteristics of both storage channels and timing channels, and a method is given for constructing all channels in a computer system that have timing channel characteristics. Since Kemmerer's shared resource matrix methodology [7] has the potential to detect all channels that have storage characteristics, it is argued that the two methods jointly have the capability to construct all channels in a computer system.

The approach to timing channels provides a justification of specific mechanisms for reducing their bandwidth which were employed in the VAX1

¹

VAX is a trademark of Digital Equipment Corporation.

Virtual Machine Monitor, as described in [4] and [5].