(This entry is written mostly for my non-cryptographer friends who wonder why I am always criticizing Estonian e-voting scheme, but it may also be interesting for cryptographers all around the globe. All opinions are my own.)
Many people probably already know that Estonia has had Internet voting since 2005. Over the years, the number of voters has increased. In the parliamentary elections this week, more than 10% of the whole population (which means even larger percentage of the population who can vote – and probably quite a large percentage of the people who actually go to vote) used Internet voting.
I paper voted.
Why? First of all, as a cryptographer, it is my job not to support insecure systems. Given the current situation in Estonia, paper-voting is the only thing that I can do, but I hope things will improve rapidly.
Here’s a short description of Estonian Internet voting protocol:
One vote attempt:
You as a voter either use an ActiveX control (or a downloadable application if you use a wrong browser/…) to log in to a secure webpage. To authenticate yourself you use an ID card (those have been obligatory in Estonia for quite a few years). After logging in, you use the GUI to select the candidate. After that, the voter computer encrypts your vote by using RSA and the key of a tallier. The result is also signed by using your private key (which is again stored in your ID card). Your computer now sends the signed & encrypted vote to the vote collector server.
You can always revote by using exactly the same procedure. The VCS only stores the latest vote by every voter. (This step was introduced to combat vote coercion/family voting — note that if everything else fails, you can go to the voting station and revoke your electronic vote by paper-voting.)
After the election period ends, the VCS will take the latest encrypted votes of all voters and send them to the second server that is behind a firewall. The second server removes all the signatures. It then ‘burns’ all the unsigned encrypted votes to a CD. Now, a number of trusted people (including observers) take this CD and bring it to a separate room, which is well guarded. That room contains the third server, the tallier who is *not* connected to Internet at all. The CD is input to the tallier. The tallier reads all encrypted votes. Since it knows the decryption keys, it can decrypt all votes. After that it outputs the number of votes given for every candidate.
This whole process also contains a number of organizational steps (like transfer of the CD to the tallier, or general auditing), but cryptographically that’s it.
So what’s wrong with it? For a cryptographer it’s a rhetoric question but let me reiterate some points. Basically, an e-voting system can be attacked by attacking voter computers, Internet connection or voting servers. Signing/encryption mostly takes care of fraudulent Internet (they do not obviously protect you against DDOS attacks and the like).
Voter computers are an obvious problem: most of the people are computer illiterate, and are not able to check if their computers are not infected. Even if they have the newest antivirus (which we can’t be sure of), that antivirus itself might not be able to detect a piece of new malware that has been written specifically for *that* election and is unleashed just before it. (Note: in Estonia e-voting lasts for 3 days.) That malware could do a lot of damage, like hijack the connection between you and the ID card (basically letting the ID card to sign wrong votes), between the GUI and what actually happens inside the computer, etc. I would *not* be surprised if such a piece of software was written by a high-school kid.
Vote servers are another problem: they can attacked by a hostile (but yet invisible) takeover, or by an insider (software provider, hardware provider, they guy with a gun meant to protect the servers, cleaning lady…). To be completely certain nothing like that happens, one should use either 100% trusted providers etc, etc (which is somewhat unlikely if an interested foreign powers invests a few million euros to bribe everybody), or one should use cryptography. But first, why does it matter? Can’t we trust the election office? Rhetorically I could ask: do we trust politicians in general? Do we? Less rhetorically, there are so many potential threats here.
Given all this, when Internet voting process started in Norway, the government officials clearly stated they want strong cryptography, and probable security in general. In particular, they do not want to only avoid attacks. They want to be able to prove that no attacks happened. Moreover, they want to be able to prove that the e-voting system is so secure that no attacks are possible at all. (Or at least, the number of possible attacks is strongly limited.) If the e-voting system satisfies that property, they can in particular prove that they did *not* cheat. That means, at least some kittens in Norway will have a good night sleep. And people’s trust in the governance will increase.
We can imagine all kind of attacks (and motivations behind those attacks) against Internet voting. A party would like to gain a few more votes. A script kiddie is angry at a politician whose daughter doesn’t like him. A foreign power wants their favorite party to gain a few more votes. A foreign power attacks e-voting process just so that it will be clear that somebody attacked and thus the results can’t be trusted. Etc. Etc. Script kiddie might spend a few days to write a virus that works on user computers. A foreign power might spend $10M to develop Stuxnet+.
How can we protect Internet voting then? Fortunately, there *are* very well-known (at least in the cryptographic community) protocols for that. It is known how to get security in the case when a minority of voting servers is malicious. Under some conditions, it just suffices to have one uncorrupted voting server. Developing such protocols means that there is a need for additional computing power (and time, to implement the cryptographic protocols). Deploying such protocols is invisible to the voters.
Protecting against corrupted voter computers is more difficult. There are quite many ways to do it, but most of the ways requires the voters to perform some additional operations. As an example, Norway will use a scheme where every voter receives (by post) a codesheet that has the names of all candidates and corresponding check codes. (The codes are unique for every voter.) Voting proceeds as usual, by using computer and your favorite GUI, but afterwards you will receive by SMS a single code. The voter can now just verify if this is the same code that was written on the codesheet under his or her favorite candidate. If it is not, he can revote electronically (or go and paper-vote).
There are a number of good things about the Norwegian system. First of all, receiving the codesheet and checking your codes is not obligatory — you just have to do it when you are paranoid or just security-conscious (or just geeky). Thus, Internet voting still rules in the sense of convenience. On the other hand, interested voters can verify that their votes were counted for by following a relatively small number of steps.
Another thing that I like about the Norwegian solution is that by using their own words, the underlying math is simple enough to be understood by high school students — and they plan to start teaching the protocol at high schools. (See the slides here.) Which is nice, since cryptography is not everything — for complete trust there have to be enough people to understand the system. And it’s always nice to teach people new math. :-)
The Norwegian system is not ideal, but it can be improved upon. There are also many other, somewhat similar (or completely different) techniques to protect Internet voting schemes against corrupted user computers. Unfortunately, dwelling into them would take quite a lot of time and this margin here is too short.