Improving the Individual Verification of Estonian Internet Voting Scheme

Estonia has been using the Estonian Internet Voting (EIV) scheme for state-wide legally binding general elections. Due to the so-called "Student Attack" mounted in 2011, an optional individual vote verification mechanism was added to EIV scheme. Then, Mus et al. has shown that this mechanism may be used for revealing the cast vote if the device, on which individual vote verification is running, is compromised. However, their practical solution is broken afterwards. The scheme has been updated with respect to the security analysis, since 2017 the framework labeled as IVXV is in use. In this study, we note that this vote privacy issue still exists in the currently used IVXV framework and suggest two counter-measures to eliminate this attack. First one is to utilize screenshot prevention methods in the individual verification application. Second one is to apply Mus et al.'s proposition in a user-friendly checking mechanism that does neither induce vote privacy leakage nor add new attack surface to the framework.