A pump for rapid, reliable, secure communication
CCS '93 Proceedings of the 1st ACM conference on Computer and communications security
Building higher resolution synthetic clocks for signaling in covert timing channels
CSFW '95 Proceedings of the 8th IEEE workshop on Computer Security Foundations
A comment on the confinement problem
SOSP '75 Proceedings of the fifth ACM symposium on Operating systems principles
On Introducing Noise into the Bus-Contention Channel
SP '93 Proceedings of the 1993 IEEE Symposium on Security and Privacy
SP '93 Proceedings of the 1993 IEEE Symposium on Security and Privacy
SP '94 Proceedings of the 1994 IEEE Symposium on Security and Privacy
SP '95 Proceedings of the 1995 IEEE Symposium on Security and Privacy
Supporting security requirements in multilevel real-time databases
SP '95 Proceedings of the 1995 IEEE Symposium on Security and Privacy
NON-DISCRETIONARY ACCESS CONTROL FOR DECENTRALIZED COMPUTING SYSTEMS
NON-DISCRETIONARY ACCESS CONTROL FOR DECENTRALIZED COMPUTING SYSTEMS
Program confinement in KVM/370
ACM '77 Proceedings of the 1977 annual conference
New constructive approach to covert channel modeling and channel capacity estimation
ISC'05 Proceedings of the 8th international conference on Information Security
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Our timed Z-channel (a general case of the Z-channel) appears as the basis for a large class of covert channels. Golomb analyzed the Z-channel, a memoryless channel with two input symbols and two output symbols, where one of the input symbols is transmitted with noise while the other is transmitted without noise, and the output symbol transmission tames are equal. We introduce the timed Z-channel, where the output symbol transmission times are different. Specifically, we show how the timed Z-channel applies to two examples of covert timing channel scenarios: a CPU scheduler, and a token ring network. We then give a detailed analysis of our timed Z-channel. We report a new result erpressing the capacity of the timed Z-channel as the log of the root of a trinomial equation. This changes the capacity calculation from an optimization problem into a simpler algebraic problem and illustrates the relationship between the noise and time factors. Furlher, it generalizes Shannon's work on noiseless channels for this special case. We also report a new result bounding the timed Z-channel's capacity from below. Finally, we show how an interesting observation that Golomb reported for the Z-channel also holds for the timed Z-channel.