Improving Sender Anonymity in a Structured Overlay with Imprecise Routing

In the framework of peer to peer distributed systems, the problem of anonymity in structured overlay networks remains a quite elusive one. It is especially unclear how to evaluate and improve {\em sender} anonymity, that is, untraceability of the peers who issue messages to other participants in the overlay. In a structured overlay organized as a chordal ring, we have found that a technique originally developed for {\em recipient} anonymity also improves sender anonymity. The technique is based on the use of imprecise entries in the routing tables of each participating peer. Simulations show that the sender anonymity, as measured in terms of average size of anonymity set, decreases slightly if the peers use imprecise routing; yet, the anonymity takes a better distribution, with good anonymity levels becoming more likely at the expenses of very high and very low levels. A better quality of anonymity service is thus provided to participants.