A method for degradation of anonymity on mix systems for E-mail and surfing the WWW
Lexi Pimenidis · 2006
Some anonymizing networks, like e.g. JAP, relay messages to external services, i.e. allow communication to entities that are not participants of the network. In general this is the case if networks provide access to the world wide web (like e.g. JAP, and Tor) or allow email messaging with pseudonymous return addresses (like e.g. Mixmaster). Even if answers are indistinguishable from requests in the anonymizing network, they can severly damage the amount of anonymity provided by a system. This is due to the fact that outside the anonymous network answers are linkable to their request, take an individual amount of time to be generated, and thus are returned to the original sender in different anonymity sets. We will show in this paper that anonymizing networks which provide access to ex-ternal services are subject to a traffic analysis that can strongly degrade the anonymity provided to their participants. The degradation is based on the fact that replies to mes-sages are linkable outside the anonymizing network. This analysis can be used as an effective measure to preproccess all kinds of anonymized communication and build a step stone for further, more elaborated, attacks. 1