Special Uses and Sbuses of the Fiat-Shamir Passport Protocol
CRYPTO '87 A Conference on the Theory and Applications of Cryptographic Techniques on Advances in Cryptology
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The purpose of this paper is to present a warning that covert channels even at very low bandwidths can be a significant threat in conjuction with sufficiently sophisticated "trojan horses".According to DOD 5200,28-STD (the orange book) covert channels with a bandwidth of under 1 bit per ten seconds need not even be audited in a trusted system.While this seems reasonable it is easy to imagine scenarios where covert channels with a flow rate much lower than this may indeed compromise vital information, if the process from which the flow originates is an intelligent trojan horse.Consider the following scenario: A trusted multi-level secure strategic logistics system with a trojan horse which is an expert system capable of detecting whether there are troop and supply movements planned, which would allow offensive action within the next week. A convert channel with the rate of one bit per day, which each day transmits this information from the expert trojan horse to an insecure process would certainly be of great value in strategic planning.In summary, when considering the maximum bandwidth requirements on convert channels, it is necessay to consider this in line with the type of information available to processes running at the higher security levels, and the degree of trust that one has in these applications.