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Validation and verification issues in e-Voting



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Validation and Verification Issues in E-Voting
Orhan Cetinkaya1, Deniz Cetinkaya2
1Institute of Applied Mathematics, METU, Ankara, Turkey
2Computer Engineering (M.Sc.), METU, Ankara, Turkey
Abstract: Electronic democracy (e-democracy) is a necessity in this era of computers and information
technology. Electronic election (e-election) is one of the most important applications of e-democracy, because
of the importance of the voters’ privacy and the possibility of frauds. Electronic voting (e-voting) is the most
significant part of e-election, which refers to the use of computers or computerised voting equipment to cast
ballots in an election. Due to the rapid growth of computer technologies and advances in cryptographic
techniques, e-voting is now an applicable alternative for many non-governmental elections. However, security
demands become higher when voting takes place in the political area.
Requirement analysis is an important part of the system design process and it is impossible to develop the
right system in the right way without correct and complete set of requirements. In the literature, many e-voting
requirements are defined. However, the researchers started to discuss the verification in e-voting recently.
Unfortunately the definitions for verifiability are inadequate and unclear; and it is categorised as individual
verifiability and universal verifiability, where they are generally misused in the literature. Moreover, validation is
not discussed yet.
This paper focuses on the importance of the validation and verification in e-voting, gives proper definitions for
validity and verifiability in e-voting and describes their relation to accuracy and robustness of the e-voting
system. This paper also states some problems to design and develop secure and verifiable e-voting systems
and provides basic requirements that any e-voting system should satisfy.
Keywords: e-voting, e-voting requirements, validation, verification, verifiability.
1. Introduction
Electronic voting (e-voting) has been an applicable alternative for many non-governmental
elections in the last decades. However, it is not easy to say that e-voting is likely to become viable
soon for governmental elections. One of the reasons for this is the security needs of e-voting. E-
voting is a security-critical application of electronic democracy (e-democracy).
E-voting is an inter-disciplinary subject and should be studied together with the experts of different
domains, such as software engineering, cryptography, politics, law, economics and social sciences.
Although many people have worked on this subject, mostly e-voting is known as a challenging topic
in cryptography. The challenge arises primarily from the need to achieve voter anonymity, in other
words to remove voter’s identity from his cast ballot in order to ensure voter privacy whereas
ensuring the e-voting has been done correctly without any violation and ensuring only eligible
voter’s votes have been counted. Therefore, e-voting has been intensively studied in the last
When paper based voting is applied, voter can be easily persuaded that his vote is counted in the
final tally since observers participate to the voting process which can be summarised as following:
On the election day, the voter, after being authenticated by an authority, receives a blank ballot,
makes his choice in a polling-booth and casts it into a ballot box in front of the authority. Then voter
signs the record list to indicate that he has voted. After the voting period is completed, the ballot
box is opened and the ballots are counted by the authorities. The counting result is announced.
After all counting results are combined, election result is publicised. Voter casts his vote by himself
without any influence and nobody can see voter’s vote except himself. Voter cannot cast more than
one vote. Vote collecting, counting and tabulating are done in front of observers publicly.
Meanwhile, representatives of political parties, observers of independent non-governmental
organizations and international organizations are welcome to be present and can observe the
election process.
When voting takes place in an electronic environment, possibility of fraud is unavoidable since
ensuring the trust is not an easy task. At any step in the e-voting process, e-voting results can be
manipulated if there is lack of validation and verification. The e-voting experience in Ohio in 2004 is
a well-known example which caused many discussions about vote miscount and modification
where its expected candidate did not match the official winner of the election.
Majority of people may accept and use e-voting, but people have some doubts about the privacy,
security and accuracy of the e-voting. They cannot easily trust the e-voting system unless
validation and verification of the system is achieved. If validation and verification (V&V) processes
are applied on e-voting systems, then the trust level will be increased and more voter participation
can easily be achieved.
In e-voting, V&V processes should be performed to assure the security and reliability of the e-
voting protocols and systems. Since an e-voting system usually depends on an e-voting protocol,
the V&V of the e-voting system typically covers V&V of the e-voting system and its underlying e-
voting protocol. In practice, V&V activities should occur both during, as well as at the end of the
development life cycle to ensure that all requirements have been fulfilled and the system works
properly. The quality of the requirements can be improved and costs and risks can be controlled by
performing V&V early in the development process.
Verifiability and verification in e-voting is started to be discussed recently. Unfortunately the
definitions for verifiability are inadequate and unclear. Moreover, verifiability is categorised as
individual verifiability and universal verifiability, where they are generally misused in the literature.
This paper states the importance of the V&V in e-voting and gives proper definitions for validation
and verification of e-voting protocols and systems. It also describes the relation between V&V and
major e-voting requirements. The remainder of the paper is organised as follows. The next section
provides an overview of e-voting and its requirements. Then related work is discussed. In Section
4, validation and verification in e-voting is explained. Finally, conclusions are drawn and future work
is suggested.
2. Overview of e-Voting
Voting is regarded as one of the most effective methods for individuals to express their opinions on
a given topic. E-voting refers to the use of computers or computerised voting equipment to cast
ballots in an election. Chaum pioneered the notion of e-voting and then many protocols were
proposed (Chaum 1981). The first practical e-voting protocol for large scale elections is of Fujioka
et al. (Fujioka 1992). Verifiability was firstly introduced in this protocol however it requires more
voter involvement and accuracy can be violated that the malicious authority can add votes if any
voter abstains from voting in the counting stage.
The basic process of any e-election is almost standard although a wide variety of e-voting systems
and protocols exist. Any e-voting system should include these actors:
Voter: Voter has the right for voting, and votes in the election.
Registration Authority(ies): Registration authority or authorities register eligible voters before the
election day. These authorities ensure that only registered voters can vote and they vote only
once on the election day.
Tallying Authority(ies): The tallying authorities collect the cast votes and tally the results of the
Any e-voting system should also involve these four phases:
Registration: Voters register themselves to registration authorities and the list of eligible voters
is compiled before the election day.
Authentication and Authorisation: On the election day registered voters request ballot or voting
privilege from the registration authorities. Registration authorities check the credentials of those
attempting to vote and only allow those who are eligible and registered before.
Voting: Voter casts his vote.
Tallying: The tallying authorities count the votes and announce the election results.
A general e-voting process and the actors involved can be summarised as in Figure 1 (Cetinkaya
2007), (Cranor 1997), (Fujioka 1992).
Figure 1: A general e-voting process
In literature, many e-voting protocols have been proposed. In those protocols, different requirement
sets are defined, and whereas fulfilling these requirements different cryptographic tools and
primitives are used. These underlying primitives are mainly blind signatures (Chaum 1982), mix-
nets (Chaum 1981) and homomorphic encryption (Benaloh 1994). Before proceeding to the related
work about V&V in e-voting protocols, we will briefly describe e-voting requirements.
2.1 E-Voting requirements
There are many e-voting requirements mentioned in e-voting protocols. We will briefly describe
major ones (Cetinkaya 2007), (Cranor 1997), (Fujioka 1992). For further reading on e-voting
requirements we refer the interested readers to the recent work of (Cetinkaya 2007). We will
describe the relation between V&V and these requirements in Section 4.1.
Privacy: It is the inability to link a voter to a vote. Voter privacy must be preserved during the
election as well as after the election for a long time.
Eligibility: Only eligible voters participate in the election. They should register before the election
day and only registered eligible voters can cast votes.
Uniqueness: Only one vote for a voter should be counted. It is important to notice that
uniqueness does not mean un-reusability, where voters should not vote more than once. Only
one vote for a voter is counted.
Uncoercibility: Any coercer, even authorities, should not be able to extract the value of the vote
and should not be able to coerce a voter to cast his vote in a particular way. Voter must be able
to vote freely.
Receipt-freeness: It is the inability to know what the vote is. Voters must neither be able to
obtain nor construct a receipt which can prove the content of their vote to a third party both
during the election and after the election ends. This is to prevent vote buying or selling.
Fairness: No partial tally is revealed before the end of the voting period to ensure that all
candidates are given a fair decision. Even the counter authority should not be able to have any
idea about the results.
Transparency: The whole voting process must be transparent. Bulletin boards may be used to
publicise the election process. The security and reliability of the system must not rely on the
secrecy of the network which cannot be guaranteed.
Accuracy: All cast votes should be counted. Any vote cannot be altered, deleted, invalidated or
copied. Any attack on the votes should be detected. Uniqueness should also be satisfied for
Robustness: Any number of parties or authorities cannot disrupt or influence the election and
final tally. To have confidence in the election results, robustness should be assured. However,
there are numerous ways for corruption. For example; registration authorities may cheat by
allowing ineligible voters to register; ineligible voters may register under the name of someone
else; ballot boxes, ballots and vote counting machines may be compromised.
3. Related work
Fujioka et al. (Fujioka 1992) pioneered the verifiability in e-voting protocols by forcing voters to
involve more than one round. Voter has to participate in the counting stage by checking that his
vote is listed correctly in the tallying list, and then sending a part of the vote in order to complete
voting. In this protocol, verifiability defined as “No one can falsify the result of the voting”.
Later, Sako et al. (Sako 1995) introduces the concept of universal verifiability to emphasise the
importance of auditing of overall election by categorising the verifiability as individual variability and
universal verifiability. Further e-voting studies apply this categorisation. Sako et al. defined
individual and universal verifiability respectively as “A sender can verify whether or not his
message has reached its destination, but cannot determine if this is true for the other voters” and
“In the course of the protocol the participants broadcast information that allows any voter or
interested third party to at a later time verify that the election was performed properly”.
Cranor et al. (Cranor 1997) makes the definition of universal verifiability narrow by limiting it as just
counting the votes and defines verifiability as “Anyone can independently verify that all votes have
been counted correctly”. Most of the later studies use this definition since it is much more specific
and measurable.
Karlof et al. (Karlof 2005) combines the verifiability definition without distinguishing universal or
individual as follows: “Verifiably cast-as-intended means each voter should be able to verify his
ballot accurately represents the vote he cast. Verifiably counted-as-cast means everyone should be
able to verify that the final tally is an accurate count of the ballots.”
It is obvious that the definitions are not unique and comprehensive. However when they are
examined in detail, it is understood that they all imply the same meaning. They use verifiability in
the sense of the validation of the final tally by the actors of the e-voting system, which can be the
voters, authorities, passive observers or trusted third parties. Unfortunately this explanation is not
adequate. “Validating the final tally”, “verifying that all votes have been counted correctly”, and
“assuring the result of the voting” …etc can be treated as some activities of the V&V processes.
So, comprehensive definitions should be stated for verifiability requirement. Moreover, validation
should be taken into consideration; it should be pointed out the difference between validation and
verification; and validity requirement should be introduced in e-voting.
We can summarise the individual verifiability and universal verifiability definitions used in the
literature respectively as following every voter can check if his vote has been properly counted”
and “anyone can check that the calculated result is correct and election is performed correctly”
(Fujioka 1992), (Sako 1995), (Cranor 1997), (Riera 1998), (He 1998), (Karlof 2005), (Chaum 2005).
Delaune et al. (Delaune 2006) formalises some of the e-voting requirements and then verifies
whether the requirements hold on particular e-voting protocols. In particular, they use the formalism
of the applied pi calculus which is a formal language similar to the pi calculus but with useful
extensions for modelling cryptographic protocols and has been used to analyse a variety of security
protocols in other domains. Verification of the requirements is illustrated on two cases studies and
has been partially automated using the Blanchet’s ProVerif tool. Delaune et al. brings the formal
verification on some of the e-voting requirements; however, they do not mention anything about the
validation issues.
The aforementioned e-voting protocols take into consideration V&V in different e-voting phases.
Table 1 illustrates this relation according to the definitions of verifiability and the protocol details.
The data in the table show that verification is generally handled in voting and tallying phases.
Table 1: Related work
Registration Authentication & Authorisation Voting Tallying
Fujioka et al. N/A Yes Yes Yes
Sako et al. N/A Yes Yes Yes
Cranor et al. No No No Yes
He et al. No No Yes Yes
Riera et al. No No No Yes
Karlof et al. No Yes Yes Yes
4. Validation & Verification (V&V) in E-Voting
Many e-voting protocols have been proposed from both theoretical and practical perspectives in
the literature. However, to the best of our knowledge, no complete solution has been found
because of the importance of security requirements in voting systems such as privacy, accuracy,
fairness and robustness.
E-voting protocols have an anonymity requirement, which means the unlinkability between the
voter and his cast vote. Anonymity is the primary requirement of the e-voting protocols in order to
satisfy voter privacy. Fraud and system violations can be done without being detected in
anonymous environments. This characteristic of e-voting forces the researchers to find a way to
persuade the voter that his vote is really counted and the voting is done properly. This requirement
is named as verifiability and used many years in the literature.
In software engineering, validation is the process of validating that the system satisfies the
intended use and fulfils the user requirements; and verification is the process of verifying that the
system complies with design specifications and formally specified properties, such as consistency
and redundancy (IEEE 1996). In other words, validation is building the right system and verification
is building the system right.
In an ideal world, a verified system would be naturally validated, but this is far from what is
currently possible in practice. Even if it is possible to specify formally all of the user requirements,
and then to verify that a system conforms to this specification, there would still be no guarantee
that the requirements were correct. Verification can be viewed as a part of validation, it is unlikely
that a system that is not "built right" to be the "right system". However, verification is unlikely to be
the whole of validation, due to the difficulty of specifying user requirements. Therefore, it seems
that validation should be more than verification.
In e-voting, validation is the process of validating that the e-voting system satisfies its intended use
and fulfils the user requirements, such as accuracy and eligibility; and verification is the process of
verifying that the e-voting system complies with design specifications and formally specified system
requirements, such as robustness and fairness. Verification also includes the review of interim work
steps and interim outputs during the e-voting process to ensure they are acceptable. Therefore,
validation tries to answer the question: “Do we apply the right protocol and build the right system?”
and verification tries to answer the question: “Do we apply the protocol and build the system right?”
According to these definitions we can state that individual verifiability used in the literature can be
treated as a part of the validation process because voter checks whether his vote is really counted
in the final tally. As well as, universal verifiability can be a part of the verification process as it is
employed to check dishonest authorities and some internal processes.
While V&V are parts of the overall system development process, they are extremely important
because they are the only way to produce a right system in a right manner. The V&V of e-voting
protocol or e-voting system are parts of the overall design and development processes. So in ideal
case V&V issues should not be handled as e-voting requirements such as verifiability or validity,
since it is expected that V&V should be performed by default. However, there are many studies
which use verifiability as a requirement. Thus, within the mentioned e-voting context we give the
definitions of validity and verifiability in order to cover those studies. Validity is the ability of
performing the validation process of the e-voting protocol or the e-voting system; and verifiability is
the ability of performing the verification process of the e-voting protocol or the e-voting system.
Besides, in order to cover individual verifiability as an e-voting requirement we offer an alternative
naming for that requirement to prevent misunderstanding: individual vote check. It means that the
voter should be able to check that his vote is counted correctly in the final tally.
In literature, the verification is misused since it represents control or check mechanisms instead of
verification process. Mostly, verifiability is used as validation and verification of any subset of the e-
voting requirements especially accuracy and robustness. However, when V&V are used in an e-
voting system, they should be applied to all requirements instead of a subset of requirements as
the V&V processes cover all steps in an e-voting system.
V&V are interrelated and complementary processes that use each other’s process results. In order
to perform V&V, some activities are specified and these activities are described in system V&V
plans. Validation activities are defined (for the voter, the authorities, or independent parties) for
validating the e-voting protocol or the e-voting system. Verification activities are defined (for the
voter, the authorities, or independent parties) for verifying the e-voting protocol or the e-voting
system in varying depth depending on the system.
Validation activities may be:
validating if the e-voting system complies with the user requirements,
checking if the e-voting system performs functions for which it is intended
checking if the e-voting system meets the specified goals,
tally validation,
ballot validation,
authentication, …etc.
Verification activities may be:
verifying if the e-voting system is consistent,
checking if the e-voting system adheres to standards,
verifying if the e-voting system uses reliable techniques and sensible practices
verifying if the e-voting system performs the selected functions in the correct manner,
checking the compatibility between the e-voting protocol and the e-voting system,
verifying if the e-voting system conforms to requirements such as correctness, completeness,
accuracy for all of the e-voting steps,
ballot testing, … etc.
In order to fully satisfy validation in e-voting protocols and e-voting systems, voter should be an
active participant. The reason is that nobody can know the voter’s cast vote except voter himself.
Thus, to validate e-voting system completely voter should involve in V&V processes during the
4.1 V&V and E-Voting Requirements
Verification is aimed at eliminating errors in the system, and is typically a low level task. Verification
is related to robustness. Validation is more concerned with the quality of the system and is typically
a high level task. Validation is related to accuracy, and the observed robustness.
Validity and verifiability is strongly related to transparency. The e-voting system should be able to
allow validation and verification. However, validity and verifiability may contradict with receipt-
freeness and uncoercibility requirements, since individual vote check requirement is clearly
conflicting with them. Moreover, accuracy and robustness may contradict with privacy.
The relation between V&V and the e-voting requirements is shown in Table 2. The relation
describes whether the requirements can be validated or verified. For example privacy can be
verified by monitoring the election; however it cannot be validated without the help of voter.
Besides, eligibility can be both verified and validated, since it does not require voter. In the table
“conditionally” refers to the dependency to the voter and “partially” refers to the possibility of
contradiction with other requirements.
Table 2: Relation between V&V and the e-voting requirements
Validation Verification
Privacy Conditionally Yes
Eligibility Yes Yes
Uniqueness Yes Yes
Uncoercibility Partially Yes
Receipt-freeness Conditionally Partially
Fairness Yes Yes
Transparency Yes Yes
Accuracy Conditionally Partially
Robustness Partially Yes
Individual vote check Conditionally Partially
In comparison to paper-based voting, e-voting may provide more verifiability as it uses
cryptographic primitives which can be formally verified. In the context of software systems, formal
verification is the act of proving or disproving the correctness of intended algorithms underlying a
system with respect to a certain formal specification or property, using formal methods of
mathematics. E-voting requirements may be formalised and formal verification may be performed.
5. Conclusion and Future Work
In this paper we first gave an overview of e-voting and its requirements and then explained the
V&V in e-voting systems. We defined validation, verification, validity and verifiability terms in e-
voting and described their relation to e-voting requirements. We also suggested an alternative
naming for individual verifiability used in the literature as individual vote check.
V&V are difficult because it is hard to know how much confidence is enough. V&V is a matter of
developing a level of confidence and so the level of V&V effort needed. Thus, requirements should
be defined clearly and the level of confidence for each requirement should be defined well.
As a future work, a common framework for V&V processes can be established and e-voting V&V
plan with all V&V activities can be defined. Moreover, V&V techniques, which can be used in e-
voting V&V processes, can be explained and research on V&V tools can be done.
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Conference Paper
This paper proposes a practical secret voting scheme for large scale elections. The participants of the scheme are voters, an administrator, and a counter. The scheme ensures the privacy of the voters even if both the administrator and the counter conspire, and realizes voting fairness, i.e., no one can know even intermediate result of the voting. Furthermore fraud by either the voter or the administrator is prohibited.
A technique based on public key cryptography is presented that allows an electronic mail system to hide who a participant communicates with as well as the content of the communication - in spite of an unsecured underlying telecommunication system. The technique does not require a universally trusted authority. one correspondent can remain anonymous to a second, while allowing the second to respond via an untraceable return address. The technique can also be used to form rosters of untraceable digital pseudonyms from selected applications. Applicants retain the exclusive ability to form digital signatures corresponding to their pseudonyms. Elections in which any interested party can verify that the ballots have been properly counted are possible if anonymously mailed ballots are signed with pseudonyms from a roster of registered voters. Another use allows an individual to correspond with a record-keeping organization under a unique pseudonym which appears in a roster of acceptable clients.
In this paper we report on some recent work to formally specify and verify electronic voting protocols. In particular, we use the formalism of the applied pi calculus: the applied pi calculus is a formal language similar to the pi calcu- lus but with useful extensions for modelling cryptographic protocols. We model several important properties, namely fairness, eligibility, privacy, receipt-freeness and coercion- resistance. Verification of these properties is illustrated on two cases studies and has been partially automated using the Blanchet's ProVerif tool.
Existe una edición impresa con el título: [International Standard ISO/IEC 12207]