A new attack on Jakobsson Hybrid Mix-Net

The Jakobsson hybrid mix-net proposed by Jakobsson and Juels, is a very practical and efficient scheme which applies symmetrical and asymmetrical cryptography concurrently to make long input messages   anonymous. In this paper a new attack on the Jakobsson hybrid mix-net is introduced. This attack infringes the faultlessness of the hybrid mix-net scheme. We will show that in this new attack, if one of the senders colludes with the first mix server, the first mix server can replace the messages of all other senders with arbitrary messages without being detected.