Abstract: Norway used e-voting in its last political election both in September 2011 and September 2013, with more than 28,000 voters using the e-voting option in 2011, and 70,000 in 2013. While some other countries use a black-box, proprietary voting solution, Norway has made its system publicly available. The underlying protocol, designed by Scytl, involves several authorities (a ballot box, a receipt generator, a decryption service, and an auditor). Of course, trusting the correctness and security of e-voting protocols is crucial in that context. In this paper, we propose a formal analysis of the protocol used in Norway, w.r.t. ballot secrecy, considering several corruption scenarios. We use a state-of-the-art definition of ballot secrecy, based on equivalence properties and stated in the applied pi-calculus.
