Five practical attacks for "optimistic mixing for exit-polls"

Abstract

Golle, Zhong, Boneh, Jakobsson, and Juels [9] recently presented an efficient mix-net, which they claim to be both robust and secure. We present five practical attacks for their mix-net, and break both its privacy and robustness. The first attack breaks the privacy of any given sender without corrupting any mix-server. The second attack requires that the first mix-server is corrupted. Both attacks are adaptations of the "relation attack" introduced by Pfitzmann [24, 23]. The third attack is similar to the attack of Desmedt and Kurusawa [4] and breaks the privacy of all senders. It requires that all senders are honest and that the last mix-server is corrupted. The fourth attack may be viewed as a novel combination of the ideas of Lim and Lee [16] and Pfitzmann [24, 23]. It breaks the privacy of any given sender, and requires that the first and last mix-servers are corrupted. This attack breaks also Jakobsson [14], including the fixed version of Mitomo and Kurosawa [18]. The fifth attack breaks the robustness in a novel way. It requires corruption of some senders and the first mix-server. This attack breaks also Jakobsson and Juels [15]. © Springer-Verlag Berlin Heidelberg 2004.