Requirements for (secure) Electronic Voting
Some time ago kuasar told me about an initiative named Partido de Internet (PdI for short). The idea is to create a political party which would vote every law proposition and every initiative in the parliament depending on the results of an individual electronic election. So, affilates would vote in a per-initiative basis through the Internet, and the representatives of the PdI in the parliament would vote according to the results.
Setting aside the political implications, whether I (or you) think this is a good idea or not, I want to talk here about electronic voting. As soon as she mentioned it to me, I started thinking "Wait... this is not so easy. You know, we want elections to be secure, one doesn't want everyone to know what he voted, but he wants his vote to be counted in the right way... there are several requirements which are not so easy to meet".
So I asked her about how would they implement it... and the answer was that probably using the e-DNI, the spanish electronic id card, which of course provides digital signatures. Yeah, that's right, you could use such a device to implement an electronic voting scheme... but there is quite a lot of thinking involved in order to make it right!
Let's start here a series of posts for brainstorming about e-voting. I'll start setting up what I (and the literature I have from last year's subjects about crypto protocols 😉 ) think an electronic voting scheme needs to provide. These are the requirements I can see, but maybe you can think of some other so feel free to comment on it!
- Privacy or Anonymity: A voter wants his vote to remain anonymous. There should be absolutely no way to link a voter with its vote, neither by other voters or by the election authorities.
- Eligibility: Only voters who are eligible for voting should be able to vote, and only once. A legitimate voter should not be able to cast two different votes, and of course a non-legitimate voter should not be able to vote.
- Fariness: The results can only be obtained at the end of the elections... so that other voters cannot be influenced.
- Verifiability: The outcome of the elections needs to be fair, i.e. the results have to be equal to the votes casted by the voters.
- Individual verifiability: An individual voter can verify that his vote was actually counted.
- Receipt free: A voter cannot prove that he voted for a given party. This way one cannot be coerced to vote for a given party.
Some of these requirements are more important than others, some of them are really required for any fair electronic voting system that one can think of, and others are just desirable. In subsequent posts we will look at some electronic voting protocols and try to see which requirements they meet.
Before finishing, one thing is clear: meeting the requirements is not trivial. For instance, vote privacy and verifiability seem to pose a contradiction... how come one can only vote if he is eligible to it, but a vote cannot be revealed to anyone? We'll see some ways of doing it in some time ;-).