A Publicly-Veri able Mix-net with Everlasting Privacy Towards Observers

In this paper we present a novel, publicly verifiable mixing scheme which has everlasting privacy towards observers: all the information published on the bulletin board by the mixes (audit information etc)̇ reveals no information about the identity of any of the messages published. The correctness of the mixing process is statistical: even if all authorities conspire, they cannot change the contents of any message without being detected with overwhelming probability. We accomplish this by encoding the messages submitted using so-called Pedersen commitments. Decoding (opening) these is possible because we create a parallel mix-net run by the same mixes to which the public has no access. This private mix-net uses the same permutations as the public one, but uses homomorphic encryption, which is used to send auxiliary information (messages, decommitment values) through the mix-net to allow decoding.