159 research outputs found
Features and usage of Belenios in 2022
Belenios is an open-source Internet voting protocol associated
to a free voting platform, launched in 2015. A detailed overview of
the protocol has been presented in [6] in 2019 and its complete, up-todate
specification is public [7]. Since 2019, the use of Belenios has significantly
increased with more than 1,400 elections organized each year in
2020 and 2021, and a total of more than 100,000 received ballots.
We report here on the new features added to Belenios since 2019 that include
weighted votes, flexible counting methods (e.g. Condorcet or STV)
thanks to mixnets, and crowdsourced translation with the support of
more than 10 languages. Moreover, we have improved the auditability of
Belenios in practice, both for voters and authorities
Privacy-Preserving Verifiability: A Case for an Electronic Exam Protocol
We introduce the notion of privacy-preserving verifiability for security protocols. It holds when a protocol admits a verifiability test that does not reveal, to the verifier that runs it, more pieces of information about the protocol’s execution than those required to run the test. Our definition of privacy-preserving verifiability is general and applies to cryptographic protocols as well as to human security protocols. In this paper we exemplify it in the domain of e-exams. We prove that the notion is meaningful by studying an existing exam protocol that is verifiable but whose verifiability tests are not privacy-preserving. We prove that the notion is applicable: we review the protocol using functional encryption so that it admits a verifiability test that preserves privacy to our definition. We analyse, in ProVerif, that the verifiability holds despite malicious parties and that the new protocol maintains all the security properties of the original protocol, so proving that our privacy-preserving verifiability can be achieved starting from existing security
Efficient cryptosystem for universally verifiable mixnets
Projecte final de carrera realitzat en col.laboració amb Scytl Secure Electronic Votin
cMix: Mixing with Minimal Real-Time Asymmetric Cryptographic Operations
We introduce cMix, a new approach to anonymous communications.
Through a precomputation, the core cMix protocol eliminates all expensive realtime
public-key operations --- at the senders, recipients and mixnodes --- thereby
decreasing real-time cryptographic latency and lowering computational costs for
clients. The core real-time phase performs only a few fast modular multiplications.
In these times of surveillance and extensive profiling there is a great need for an
anonymous communication system that resists global attackers.
One widely recognized
solution to the challenge of traffic analysis is a mixnet, which anonymizes
a batch of messages by sending the batch through a fixed cascade of mixnodes.
Mixnets can offer excellent privacy guarantees, including unlinkability of sender
and receiver, and resistance to many traffic-analysis attacks that undermine many
other approaches including onion routing. Existing mixnet designs, however, suffer
from high latency in part because of the need for real-time public-key operations.
Precomputation greatly improves the real-time performance of cMix, while
its fixed cascade of mixnodes yields the strong anonymity guarantees of mixnets.
cMix is unique in not requiring any real-time public-key operations by users.
Consequently, cMix is the first mixing suitable for low latency chat for lightweight
devices.
Our presentation includes a specification of cMix, security arguments, anonymity
analysis, and a performance comparison with selected other approaches. We also
give benchmarks from our prototype
Secure multi party computations for electronic voting
Στην παρούσα εργασία, μελετούμε το πρόβλημα της ηλεκτρονικής ψηφοφορίας.
Θεωρούμε ότι είναι έκφανση μιας γενικής διαδικασίας αποφάσεων που μπορεί να
υλοποιηθεί μέσω υπολογισμών πολλαπλών οντοτήτων, οι οποίοι πρέπει να
ικανοποιούν πολλές και αντικρουόμενες απαιτήσεις ασφαλείας.
Έτσι μελετούμε σχετικές προσεγγίσεις οι οποίες βασιζονται σε κρυπτογραφικές
τεχνικές, όπως τα ομομορφικά κρυπτοσυστήματα, τα δίκτυα μίξης και οι τυφλές
υπογραφές. Αναλύουμε πώς προσφέρουν ακεραιότητα και ιδιωτικότητα (μυστικότητα)
στην διαδικασία και την σχέση τους με την αποδοτικότητα. Εξετάζουμε τα είδη
λειτουργιών κοινωνικής επιλογής που μπορούν να υποστηρίξουν και παρέχουμε δύο
υλοποιήσεις. Επιπλέον ασχολούμαστε με την αντιμετώπιση ισχυρότερων αντιπάλων μη
παρέχοντας αποδείξεις ψήφου ή προσφέροντας δυνατότητες αντίστασης στον
εξαναγκασμό. Με βάση την τελευταία έννοια προτείνουμε μια τροποποίηση σε ένα
ευρέως χρησιμοποιούμενο πρωτόκολλο. Τέλος μελετούμε δύο γνωστές υλοποιήσεις
συστημάτων ηλεκτρονικής ψηφοφοριας το Helios και το Pret a Voter .In this thesis, we study the problem of electronic voting as a general decision
making process that can be implemented using multi party computations,
fulfilling strict and often conflicting security requirements. To this end, we
review relevant cryptographic techniques and their combinations to form voting
protocols. More specifically, we analyze schemes based on homomorphic
cryptosystems, mixnets with proofs of shuffles and blind signatures. We analyze
how they achieve integrity and privacy in the voting process, while keeping
efficiency. We examine the types of social choice functions that can be
supported by each protocol. We provide two proof of concept implementations.
Moreover, we review ways to thwart stronger adversaries by adding receipt
freeness and coercion resistance to voting systems. We build on the latter
concept to propose a modification to a well known protocol. Finally, we study
two actual e-Voting implementations namely Helios and Pret a Voter
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