We study mix-nets with randomized partial checking (RPC) as proposed by Jakobsson, Juels, and Rivest (2002). RPC is a technique to verify the correctness of an execution both for Chaumian and homomorphic mix-nets. The idea is to relax the correctness and privacy requirements to achieve a more efficient mix-net. We identify serious issues in the original description of mix-nets with RPC and show how to exploit these to break both correctness and privacy, both for Chaumian and homomorphic mix-nets. Our attacks are practical and applicable to real world mix-net implementations, e.g., the Civitas and the Scantegrity voting systems.

We construct a provably secure mix-net from any CCA2 secure cryptosystem. The mix-net is secure against active adversaries that statically corrupt less than λ out of k mix-servers, where λ is a threshold parameter, and it is robust provided that at most min(λ - 1, k - λ) mix-servers are corrupted. The main component of our construction is a mix-net that outputs the correct result if all mix-servers behaved honestly, and aborts with probability 1 - O(H-(t-1)) otherwise (without disclosing anything about the inputs), where t is an auxiliary security parameter and H is the number of honest parties. The running time of this protocol for long messages is roughly 3tc, where c is the running time of Chaum's mix-net (1981).

We study the heuristically secure mix-net proposed by Puiggalí and Guasch (EVOTE 2010). We present practical attacks on both correctness and privacy for some sets of parameters of the scheme. Although our attacks only allow us to replace a few inputs, or to break the privacy of a few voters, this shows that the scheme can not be proven secure.

We study the heuristically secure mix-net proposed by Puiggal´ı and Guasch (EVOTE2010). We present practical attacks on both correctness and privacy for some sets of parametersof the scheme. Although our attacks only allow us to replace a few inputs, or tobreak the privacy of a few voters, this shows that the scheme can not be proven secure.

We study mix-nets with randomized partial checking (RPC) as proposed by Jakobsson, Juels, and Rivest (2002). RPC is a technique to verify the correctness of an execution both for Chaumian and homomorphic mix-nets. The idea is to relax the correctness and privacy requirements to achieve a more efficient mix-net.

We identify serious issues in the original description of mix-nets with RPC and show how to exploit these to break both correctness and privacy, both for Chaumian and homomorphic mix-nets. Our attacks are practical and applicable to real world mix-net implementations, e.g., the Civitas and the Scantegrity voting systems.

This paper presents improved collision attacks on round-reduced variants of the hash function CubeHash, one of the SHA-3 second round candidates. We apply two methods for finding linear differential trails that lead to lower estimated attack complexities when used within the framework introduced by Brier,.Khazaei, Meier and Peyrin at ASIA-CRYPT 2009. The first method yields trails that are relatively dense at the beginning and sparse towards the end. In combination with the condition function concept; such trails lead to much faster collision attacks. We demonstrate this by providing a. real collision for CubeHash-5/96. The second method randomizes the search for highly probable linear differential trails and leads to significantly better attacks for up to eight rounds.