In one of the most fiercely contested elections in years, the turnout of the 2015 British general election was still stubbornly low at 66.1% – only a single percentage point more than in 2010, and still around 10 points lower than the ranges common before the 1990s. There has been all manner of hand-wringing about how to improve voter engagement and turnout. Considering the huge range of things we now do online, why not voting too? A Lodestone political survey suggested that 60% of respondents said they would vote if they could do so online, and this rose to around 80% among those aged 18-35. As recently as this year, the speaker of the House of Commons called for a secure online voting system by 2020. But designing a secure way to vote online is hard. An electronic voting system has to be transparent enough that the declared outcome is fully verifiable, yet still protect the anonymity of the secret ballot in order to prevent the possibility of voter coercion.
Any online voting system has to arrive at its conclusion in such a way that voters and observers can verify the count, independently of the software used – this is called end-to-end verifiability. This way voters can be assured that their votes were recorded as they were cast, and that all cast votes were counted correctly.
The vital nature of this can be explained by analogy to online banking. Bank customers can verify their own bank statements – and need not care about the software that produced them. But what if the banks provided no evidence of your transactions, just your remaining balance – how could you verify that the bank wasn’t cheating you?
The difficulty in respect of online voting is that how each voter cast their vote must be kept secret – we can’t just have a huge banking-like “statement” recording who voted which way. Instead, all the votes cast are gathered together and presented on a website in encrypted form, in order to ensure ballot secrecy.