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\section*{Handout 2 (E-Voting)}

In security engineering, there are many counter-intuitive

phenomena: for example I am happy (more or less) to use online

banking every day, where if something goes wrong, I can

potentially lose a lot of money, but I am staunchly against

using electronic voting (let's call it e-voting for short).

E-voting is an idea that is nowadays often promoted in order

to counter low turnouts in elections\footnote{In my last local

election where I was eligible to vote only 48\% of the

population have cast their ballot. I was, I shamefully admit,

one of the non-voters.} and generally sounds like a good idea.

Right? Voting from the comfort of your own home, or on your

mobile on the go, what could possibly go wrong? Even the UK's

head of the Electoral Commission, Jenny Watson, argued in 2014

in a Guardian article that the UK should have e-voting. Her

plausible argument is that 76\% of pensioners in the UK vote

(in a general election?), but only 44\% of the under-25s. For

which constituency politicians might therefore make more

favourable (short-term) decisions is clear. So being not yet

pensioner, I should be in favour of e-voting, no?

Well, it turns out there are many things that can go wrong

with e-voting, as I like to argue in this handout. E-voting in

a ``secure way'' seems to be one of the things in computer

science that are still very much unsolved. It is not on the

scale of Turing's halting problem, which is proved that it can

never be solved in general, but more in the category of being

unsolvable with current technology. This is not just my

opinion, but also shared by many security researchers amongst

them Alex Halderman, who is the world-expert on this subject

and from whose Coursera course on Securing Digital Democracy I

have most of my information and inspiration. It is also a

controversial topic in many countries:

\begin{itemize}

\item The Netherlands between 1997--2006 had electronic voting

      machines, but ``hacktivists'' had found they can be

      hacked to change votes and also emitted radio signals

      revealing how you voted.

\item Germany conducted pilot studies with e-voting, but in

      2007 a law suit has reached the highest court and it

      rejected e-voting on the grounds of not being

      understandable by the general public.

\item UK used optical scan voting systems in a few trail

      polls, but to my knowledge does not use any e-voting in

      elections.

\item The US used mechanical machines since the 1930s, later

      punch cards, now DREs and optical scan voting machines.

      But there is a lot of evidence that DREs and optical 

      scan voting machines are not as secure as they should

\item Estonia used since 2007 the Internet for national

      elections. There were earlier pilot studies for voting

      via Internet in other countries.

\item India uses e-voting devices since at least 2003. They

      use ``keep-it-simple'' machines produced by a

      government owned company.

\item South Africa used software for its tallying in the 1993

      elections (when Nelson Mandela was elected) and found

      that the tallying software was rigged, but they were

      able to tally manually. 

\end{itemize}

The reason that e-voting is such a hard problem is that we

have requirements about the voting process that conflict with

each other. The five main requirements for voting in general

are:

\begin{itemize}

\item {\bf Integrity} 

  \begin{itemize}

  \item By this we mean that the outcome of the vote matches

        with the voters' intend. Note that it does not say

        that every vote should be counted as cast. This might

        be surprising, but even counting paper ballots will

        always have an error rate: people after several hours

        looking at ballots will inevitably miscount votes. But

        what should be ensured is that the error rate does not

        change the outcome of the election. Of course if

        elections continue to be on knives edges we need to

        strive for rather small error rates. 

  \item There might be gigantic sums at stake and need to be

        defended against. The problem with this is that if

        the incentives are great and enough resources are

        available, then maybe it is feasible to mount a DoS

        attack against the voting server and by bringing the

        system to its knees, change the outcome of an

        election. Not to mention to hack the complete

        system with malware and change votes undetectably.                

  \end{itemize}

\item {\bf Ballot Secrecy}

  \begin{itemize}

  \item Nobody can find out how you voted. This is to avoid

        that voters can be coerced to vote in a certain way

        (for example by relatives, employers etc).

     \item (Stronger) Even if you try, you cannot prove how

           you voted. The reason for this is that you want to

           avoid vote coercion, but also vote selling. That

           this can be a problem is proved by the fact that

           some jokers in the recent Scottish referendum tried

           to make money out of their vote. \end{itemize}

\item {\bf Voter Authentication}

  \begin{itemize}

  \item Only authorised voters can vote up to the permitted

        number of votes (in order to avoid the ``vote early,

        vote often'').

  \end{itemize}

\item {\bf Enfranchisement}

  \begin{itemize}

  \item Authorised voters should have the opportunity to vote.

        This can, for example, be a problem if you make the

        authorisation dependent on an ID card, say a driving

        license. Then everybody who does not have a license

        cannot vote. While this sounds an innocent

        requirement, in fact some parts of the population for

        one reason or another just do not have driving

        licenses. They are now excluded. Also if you insist on

        paper ballots you have to have special provisions for

        blind people. Otherwise they too cannot vote.

 \end{itemize}

\item {\bf Availability}

  \begin{itemize}

  \item The voting system should accept all authorised votes

        and produce results in a timely manner. If you move

        an election online, you have to guard against DoS 

        attacks for example.

   \end{itemize}

\end{itemize}

\noindent While these requirements seem natural, the problem 

is that they often clash with each other. For example

\begin{center}

integrity vs.~ballot secrecy\\

authentication vs.~enfranchisement

\end{center}

\noindent If we had ballots with complete voter

identification, then we can improve integrity because we can

trace back the votes to the voters. This would be good when

verifying the results or when recounting. But such an

identification would violate ballot secrecy (you can prove to

somebody else how you voted). In contrast, if we remove all

identification for ensuring ballot secrecy, then we have to

ensure that no ``vote-stuffing'' occurs. Similarly, if we

improve authentication by requiring to be present at the

polling station with an ID card, then we exclude absentee

voting.

To tackle the problem of e-voting, we should first have a look

into the history of voting and how paper-based ballots

evolved. Because also good-old-fashioned paper ballot voting

is not entirely trivial and immune from being hacked. We know

for sure that elections were held in Athens as early as 600

BC, but might even date to the time of Mesopotamia and also in

India some kind of republics might have existed before the

Alexander the Great invaded it. Have a look at Wikipedia about

the history of democracy for more information. These elections

were mainly based on voting by show of hands. While this

method of voting satisfies many of the requirements stipulated

above, the main problem with hand voting is that it does not

guaranty ballot secrecy. As far as I know the old Greeks and

Romans did not perceive this as a problem, but the result was

that their elections favoured rich, famous people who had

enough resources to swing votes. Even using small coloured

stones, which were also used at that time, did not really

mitigate the problem with ballot secrecy. The problem of

authorisation was solved by friends or neighbours vouching for

you to prove you are eligible to vote (there were no ID cards

in ancient Greece and Rome).

Starting with the French Revolution and the US constitution,

people began to value a more egalitarian approach to voting

and electing officials. This was also the time where paper

ballots started to become the prevailing form of casting

votes. While more resistant against voter intimidation, paper

ballots need a number of security mechanisms to avoid fraud.

For example you need voting booths for being able to fill out

the ballot in secret. Also transparent ballot boxes are often

used in order to easily detect and prevent vote stuffing

(prefilling the ballot box with false votes). 

\begin{center}

\includegraphics[scale=2.5]{../pics/ballotbox.jpg}

\end{center}

\noindent Another security mechanism is to guard the ballot

box against any tampering during the election until counting.

The counting needs to be done by a team potentially involving

also independent observers. 

One interesting attack against completely anonymous paper

ballots is called \emph{chain vote attack}. It works if the

paper ballots are given out to each voter at the polling

station. Then an attacker can give the prefilled ballot to a

voter. The voter uses this prefilled ballot to cast the vote,

and then returns the empty ballot paper back to the attacker who now

compensates the voter. The blank ballot can be reused for the

next voter. 

To sum up, the point is that paper ballots have evolved over some time 

and no single best method has emerged for preventing fraud.

But the involved technology is well understood in order to

provide good enough security with paper ballots.

\subsection*{E-Voting}

If one is to replace paper ballots by some electronic

mechanism, one should always start from simple premise taken

from an Australian white paper about e-voting:

\begin{quote} \it ``Any electronic voting system should

provide at least the same security, privacy and transparency

as the system it replaces.''

\end{quote}

\noindent Whenever people argue in favour of e-voting they

seem to be ignoring this basic premise.\bigskip

\noindent After the debacle of the Florida presidential

election in 2000, many voting pre\-cincts in the US used

Direct-Recording Electronic voting machines (DREs) or optical

scan machines. One popular model of DREs was sold by a

company called Diebold. In hindsight they were a complete

disaster: the products were inadequate and the company

incompetent. Direct recording meant that there was no paper

trail, the votes were directly recorded on memory cards. Thus

the voters had no visible assurance whether the votes were

correctly cast. Even if there is a printout provided;

it does not give any guaranty about what is recorded on

the memory card.

The machines behind these DREs were ``normal'' Windows

computers, which could be used for anything, for example for

changing votes. Why did nobody at Diebold think of that? I

have no idea. But that this was eventually done undetectably

is the result of the determination of ethical hackers like

Alex Halderman. His group thoroughly hacked Diebold's DREs

showing that election fraud with them is easily possible. They

even managed to write a virus that infected the whole system

by having only access to a single machine.

\begin{figure}[t]

\begin{center}

\begin{tabular}{c}

\includegraphics[scale=0.45]{../pics/dre1.jpg}\; 

\includegraphics[scale=0.40]{../pics/dre2.jpg}\smallskip\\

\includegraphics[scale=0.5]{../pics/opticalscan.jpg} 

\end{tabular}

\end{center}

\caption{Direct-Recording Electronic voting machines above;

an optical scan machine below.\label{machines}}

\end{figure}

What made matters worse was that Diebold tried to hide their

incompetence and the inferiority of their products by

requiring that election counties must not give the machines up

for independent review. They also kept their source code

secret. This meant Halderman and his group had to obtain a

machine not through the official channels. They then had to

reverse engineer the source code in order to design their

attack. What all this showed is that a shady security design

is no match for a determined hacker. 

Apart from the obvious failings (for example no paper trail),

this story also told another side. While a paper ballot box

need to be kept secure from the beginning of the election

(when it needs to be ensured it is empty) until the end of the

day, electronic voting machines need to be kept secure the

whole year. The reason is of course that one cannot see

whether somebody has tampered with the program a computer is

running. Such a 24/7 security is costly and often even

impossible, because voting machines need to be

distributed---usually the day before the election---to the

polling stations. These are often schools where the voting

machines are kept unsecured overnight. The obvious solution of

putting seals on computers did not work: in the process of

getting these DREs discredited (involving court cases) it was

shown that seals can easily be circumvented. The moral of this

story is that election officials were incentivised with money

by the central government to obtain new voting equipment and

in the process fell prey to pariahs which sold them a

substandard product. Diebold was not the only pariah in this

area, but one of the more notorious ones.

Optical scan machines are slightly better from a security

point of view but by no means good enough. Their main idea

is that the voter fills out a paper ballot, which is then 

scanned by a machine. At the very least the paper ballot can 

serve as a paper trail in cases an election result needs to

be recounted. But if one takes the paper ballots as the 

version that counts in the end, thereby using the optical 

scan machine only as a device to obtain quickly preliminary

results, then why not sticking with paper ballots in the 

first place?\bigskip 

\noindent An interesting solution for e-voting was designed in

India. Essentially they designed a bespoke voting device,

which could not be used for anything else. Having a bespoke

device is a good security engineering decision because it

makes the attack surface much smaller. If you have a

full-fledged computer behind your voting system, then you can

do everything a computer can do\ldots{}and that is a lot,

including a lot of abuse. What was bad about the devices in

India was that these machines did not have the important paper

trail: that means if an election was tampered with, nobody

would find out. Even if they had by their bespoke design a

very small attack surface, ethical hackers were still able to

tamper with them. The moral with Indian's voting machines is

that even if very good security design decisions are taken,

e-voting is very hard to get right.\bigskip 

\noindent This brings us to the case of Estonia, which held in

2007 the worlds first general election that used the Internet.

Again their solution made some good choices: for example voter

authentication is done via the Estonian ID card, which

contains a chip like on credit cards. They also made most of

their source code public for independent scrutiny. Of course

this openness means that people (hackers) will look at your

fingers and find code such as this snippet.

{\footnotesize\lstinputlisting[language=Python,numbers=none]

{../progs/estonia.py}}

\noindent If you want to have a look at their code it can be

downloaded from their github

repository.\footnote{\url{https://github.com/vvk-ehk/evalimine/}}

Also their system is designed such that Internet voting is

used before the election: votes can be changed an unlimited

amount of times; always the last vote is tabulated. You can

even change your vote on the polling day in person. This is an

important security mechanism guarding against vote coercion,

which of course is an important problem if you are allowed to

vote via Internet.

However, the weak spots in any Internet voting system are the

voters' computers and the central server. Unfortunately, their

system is designed such that they needs to trust the integrity

of voters’ computers, central server components and also the

election staff. In 2014, a group of independent observers around

Alex Halderman were able to scrutinise the election process in

Estonia. They found many weaknesses, for example careless

handling of software updates on the servers. They also

simulated an election with the available software and were

able to covertly manipulate results by inserting malware on

the voters' computers. Overall, their recommendation is 

to abandon Internet voting and to go back to an entirely

paper-based voting process. In face of state-sponsored

cyber-crime (for example NSA), Internet voting cannot be made

secure with current technology. They have a small video

clip with their findings at

\begin{center}

\url{https://estoniaevoting.org}

\end{center}

\noindent This brings us to the question, what could be a

viable electronic voting process in

\underline{\textbf{\emph{theory}}} with current technology?

In the literature one can find proposals such as this one:

\begin{enumerate}

\item Alice prepares and audits some ballots, then casts an

      encrypted ballot, which requires her to authenticate to

      a server.

\item A bulletin board posts Alice's name and encrypted

      ballot. Anyone, including Alice, can check the bulletin

      board and find her encrypted vote posted. This is to

       make sure the vote was received by the server.

\item When the election closes, all votes are shuffled and the

      system produces a non-interactive proof of a correct

      shuffling---correct in the sense that one cannot determine

       anymore who has voted for what. This will require a 

       shuffling procedure based on zero-knowledge-proofs.

\item After a reasonable complaint period, let auditors

      check the shuffling, all shuffled ballots are decrypted,

      and the system provides a decryption proof for each

      decrypted ballot. Again this will need a 

      zero-knowledge-proof-type of method.

\item Perform a tally of the decrypted votes.

\item An auditor can download the entire (shuffled) election

      data and verify the shuffle, decryptions and tally.

\end{enumerate}

\noindent As you can see, the whole process is not trivial at

all and leaves out a number of crucial details (such as how to

best distribute public keys for encryption). It even depends

on a highly sophisticated process called

\emph{zero-knowledge-proofs}. They essentially allow one to

convince somebody else to know a secret without actually

revealing what the secret is. This is a kind of cryptographic

``magic'', like the Hellman-Diffie protocol which can be used

to establish a secret even if you can only exchange postcards

with your communication partner. We will look at

zero-knowledge-proofs in a later lecture in more detail. 

The point of these theoretical/hot-air musings is to show that

such an e-voting procedure is far from convenient: it takes

much more time to allow, for example, scrutinising whether the

votes were cast correctly. Very likely it will also not pass

the benchmark of being understandable to Joe Average. This was

a standard, a high court ruled, that needs to be passed in the

German election process. 

The overall conclusion is that an e-voting process involving

the Internet cannot be made secure with current technology.

Voting has just too high demands on integrity and ballot

secrecy. This is different from online banking where the whole

process is designed around authentication. If fraud occurs,

you try to identify who did what (somebody’s account got zero;

somewhere the money went). Even if there might be more 

gigantic sums at stake in online banking than with voting,

it can be solved. That does not mean there are no problems

with online banking. But with enough thought, they can

usually be overcome with technology we have currently. This

is different with e-voting: even the best have not come

up with something workable yet.

This conclusion does not imply that in some special cases

of Internet voting cannot be made to work securely. Just in a

general election where stakes are very high, it does not work.

For example a good-enough and workable in-lecture online

voting system where students' votes are anonymous and students

cannot tamper with the outcome, I am sure, can be implemented. 

\subsubsection*{Further Reading}

If you want to know more about e-voting, I recommend

the highly entertaining online course by Alex Halderman at

Coursera.

\begin{center}

\url{https://www.coursera.org/course/digitaldemocracy}

\end{center}

\noindent There is also an entertaining TEDtalk by Barbara

Simons called ``Why can I bank online but not vote online?''

\begin{center}

\url{https://www.youtube.com/watch?v=Wv3VuGZzdK8}

\end{center}

\noindent At the beginning she describes the complete break-in

by the group of Alex Halderman at the try-out voting at

\begin{center}

\url{https://jhalderm.com/pub/papers/dcvoting-fc12.pdf}

\end{center}