Breaking and Provably Fixing Minx

In 2004, Danezis and Laurie proposed Minx, an encryption protocol and packet format for relay-based anonymity schemes, such as mix networks and onion routing, with simplicity as a primary design goal. Danezis and Laurie argued informally about the security properties of Minx but left open the problem of proving its security. In this paper, we show that there cannot be such a proof by showing that an active global adversary can decrypt Minx messages in polynomial time. To mitigate this attack, we also prove secure a very simple modification of the Minx