Anonymity and Covert Channels in Simple Timed Mix-firewalls
NAVAL RESEARCH LAB WASHINGTON DC CENTER FOR HIGH ASSURANCE COMPUTING SYSTEMS (CHACS)
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Traditional methods for evaluating the amount of anonymity afforded by various Mix configurations have depended on either measuring the size of the set of possible senders of a particular message the anonymity set size, or by measuring the entropy associated with the probability distribution of the messages possible senders. This paper explores further an alternative way of assessing the anonymity of a Mix system by considering the capacity of a covert channel from a sender behind the Mix to an observer of the Mixs output. Initial work considered a simple model 5, with an observer Eve restricted to counting the number of messages leaving a Mix configured as a rewall guarding an enclave with one malicious sender Alice and some other naive senders Cluelessis. Here, we consider the case where Eve can distinguish between multiple destinations, and the senders can select to which destination their message if any is sent each clock tick.
- Computer Systems Management and Standards