Attacks on cMix - Some Small Overlooked Details

Chaum et al. have very recently introduced cMix as the first practical system that offers senders-recipients unlinkability at scale. cMix is claimed by its authors to be secure unless all nodes collude. We argue their assertion does not hold for the basic description of the protocol and sustain our statement by two different types of attacks: tagging attack and insider attack. For each one, we discuss the settings that make it feasible and possible countermeasures. By this, we highlight the necessity of implementing additional mechanisms that at first have been overlooked or have only been mentioned as additional features.