pMIX: Untraceability for Small Hiding Groups.

MIXes are routers that accept packets until their buffers are full, and then send them to the recipients hiding the link (usually through reencryption and rearrangement) between incoming and outgoing packets. MIXes and their variants are used today to provide untraceable communication with systems such as TOR, and they have been a major issue of research on privacy protection for more than twenty years. One of the major problems presented by a MIX is that its administrator is able to link the incoming and outgoing messages transiting through it, and this is the reason why MIXes are almost always organized in networks, according to the model presented by David Chaum (1981). In this paper, we present a protocol that combines these two fields of research, allowing us to create MIXes that have the remarkable property of being unable to link the incoming and outgoing packets transiting through them. This brings the possibility for its users to be untraceable while most of the data of their communication are sent through a single MIX, improving the performance and versatility of anonymizing systems