More Efficient Shuffle Argument from Unique Factorization.

Efficient shuffle arguments are essential in mixnet-based e-voting solutions. Terelius and Wikström (TW) proposed a 5-round shuffle argument based on unique factorization in polynomial rings. Their argument is available as the Verificatum software solution for real-world developers, and has been used in real-world elections. It is also the fastest non-patented shuffle argument. We will use the same basic idea as TW but significantly optimize their approach. We generalize the TW characterization of permutation matrices; this enables us to reduce the communication without adding too much to the computation. We make the TW shuffle argument computationally more efficient by using Groth’s coefficient-product argument (JOC 2010). Additionally, we use batching techniques. The resulting shuffle argument is the fastest known ≤ 5-message shuffle argument, and, depending on the implementation, can be faster than Groth’s argument (the fastest 7-message shuffle argument).