A Description and Proof of a Generalised and Optimised Variant of Wikström's Mixnet
This work addresses the need for efficient and secure verifiable mixnets in cryptographic applications, though it is incremental as it builds on existing methods.
The paper presents an optimized variant of Wikström's mixnet that enables parallel shuffling of ElGamal ciphertext vectors, and provides a detailed security proof for this construction.
In this paper, we describe an optimised variant of Wikström's mixnet which shuffles vectors of ElGamal ciphertexts in parallel. We then show in detail that this construction is secure. Wikström's verifiable mixnet as we refer to it here was first presented in "Proofs of Restricted Shuffles" by Terelius and Wikström, building on Wikström's previous work. Specifically we take the optimised variant for ElGamal which appears to be in common use; for instance, it is presented in Haenni et al's "Pseudo-Code Algorithms for Verifiable Re-Encryption Mix-Nets". We extend the mixnet to support parallel shuffles. (The possibility of doing this is proven by the Wikström's result but we wish to show that this particular instance with its optimisations is secure.)