A Peered Bulletin Board for Robust Use in Verifiable Voting Systems

The Web Bulletin Board (WBB) is a key component of verifiable election systems. It is used in the context of election verification to publish evidence of voting and tallying that voters and officials can check, and where challenges can be launched in the event of malfeasance. In practice, the election authority has responsibility for implementing the web bulletin board correctly and reliably, and will wish to ensure that it behaves correctly even in the presence of failures and attacks. To ensure robustness, an implementation will typically use a number of peers to be able to provide a correct service even when some peers go down or behave dishonestly. In this paper we propose a new protocol to implement such a Web Bulletin Board, motivated by the needs of the vVote verifiable voting system. Using a distributed algorithm increases the complexity of the protocol and requires careful reasoning in order to establish correctness. Here we use the Event-B modelling and refinement approach to establish correctness of the peered design against an idealised specification of the bulletin board behaviour. In particular we show that for n peers, a threshold of t > 2n/3 peers behaving correctly is sufficient to ensure correct behaviour of the bulletin board distributed design. The algorithm also behaves correctly even if honest or dishonest peers temporarily drop out of the protocol and then return. The verification approach also establishes that the protocols used within the bulletin board do not interfere with each other. This is the first time a peered web bulletin board suite of protocols has been formally verified.Comment: 49 page

Performance Testing Bulletin Board Implementations for Online Voting

Internetihääletamine (i-hääletamine) on hääletamisviis, mille puhul hääl liigub valija seadmest urni Interneti vahendusel. I-hääletamise süsteemide sagedaseks komponendiks on avalik teadetetahvel, kuhu registreeritud andmete abil tagatakse valimiste läbipaistvus ja auditeeritavus. Avalik teadetetahvel on komponent, mis võimaldab registreeridaandmeid viisil, mis muudab nende hilisema muutmise või kustutamise keeruliseks.Teadetetahvli puhul on oluline teenuse tagatud kättesaadavus ja toimimine. Sellest tulenevalt on avaliku teadetetahvli implementeerimise tuumküsimuseks korrektne masinate kordistamine, mille muudab keerulisemaks i-hääletamise spetsiifilised lisanõuded. Selle töö käigus käsitletakse kahte olemasolevat tarkvaralahendust, mida saab kasutada teadetetahvli realiseerimisel, uurides nende jõudlust testkeskkonnas, mis imiteerib pärisvalimiste töökoormust.Online voting is an electronic voting method in which the process of casting a vote is done using the Internet as its communication medium. One component of some online voting systems is a public bulletin board (PBB), used to provide election transparency and correctness verifiability. PBB is a component for publishing data in a way that makes modifying or deleting already published data very difficult without leaving evidence of such actions. The security and liveness of this component has to be ensured. This means that implementing PBB is a machine replication problem at its core with some specific requirements inherited from the context of online voting. This work takes a look at two software solutions that can be used for such purpose and analyses their performance in testing environment imitating real election workload

Implementing broadcast channels with memory for electronic voting systems

To provide universal verifiability, cryptographic voting protocols often require a broadcast channel to spread the election data to the public. The basic requirements on such a broadcast channel are similar for most protocols, for example that the channel maintains a memory of all broadcast messages and that nothing can be deleted from the channel’s memory. In this paper, we provide a formal definition for such broadcast channels with memory and describe their properties. We also analyze the significance of a broadcast channel with memory in cryptographic voting protocols and propose that such a channel is provided in form of a service that we call bulletin board. Based on this service, we analyze some real-world problems that cryptographic voting protocols might have and provide possible solutions. For this we define a generic interface for the main board functionalities, which offers a flexible way of extending the basic properties of a bulletin board to comply with all sorts of additional requirements

VeraSel: Verifiable Random Selection for Mixnets Construction

The security and performance of Mixnets depends on the trustworthiness of the Mixnodes in the network. The challenge is to limit the adversary's influence on which Mixnodes operate in the network. A trusted party (such as the Mixnet operator) may ensure this, however, it is a single point of failure in the event of corruption or coercion. Therefore, we study the problem of how to select a subset of Mixnodes in a distributed way for Mixnet construction. We present VeraSel, a scheme that enables Mixnodes to be chosen according to their weights in a distributed, unbiased, and verifiable fashion using Verifiable Random Functions (VRFs). It is shown that VeraSel enables any party to learn and verify which nodes has been selected based on the commitments and proofs generated by each Mixnode with VRF

Extending Helios Towards Private Eligibility Verifiability

We show how to extend the Helios voting system to provide eligibility verifiability without revealing who voted which we call private eligibility verifiability. The main idea is that real votes are hidden in a crowd of null votes that are cast by others but are indistinguishable from those of the eligible voter. This extended Helios scheme also improves Helios towards receipt-freeness

On Secure Bulletin Boards for E-Voting

Peaaegu iga elektroonilise hääletamise protokolli esimeseks etapiks on häälte kogumine ning nende talletamine. Seda teenust pakub teadetetahvlisüsteem (bulletin board). Paljud teadusartiklid eeldavad turvalise teadetetahvlisüsteemi olemasolu, kuid konkreetseid süsteeme on välja pakutud vähe. Tihti eeldatakse, et teadetetahvlisüsteem on tsentraalne usaldatav osapool, kuid hiljutistes töödes on tähelepanu juhitud tõrkekindla hajustalletuse olulisusele. Käesolevas töös pakume välja formaalse mudeli teadetetahvlisüsteemi funktsionaalsuse ning turvalisuse analüüsimisseks. Meie mudeli aluseks on Culnane ja Schneideri poolt konverentsil Computer Security Foundations Symposium 2014 väljapakutud teadetetahvlisüsteemi omadused. Me käsitleme turvalist teadetetahvlisüsteemi kui Garay ja teiste poolt konverentsil Eurocrypt 2015 tutvustatud avalikku tehingute pearaamatut, mis õnnestunud hääle talletamise korral väljastab kviitungi. Täpsemalt, me defineerime omadused (tõendatav) püsivus ning tõendatav elusus.Me analüüsime Culnane ja Schneideri väljapakutud teadetetahvlisüsteemi turvalisust ning näitame, et nende protokolli korral ei ole elususe omadus täidetud, kui mõni kogumisneel (item collection peer) on ebaaus. Nende süsteem saavutab tõendatava püsivuse kasutades triviaalset lävisignatuuri juhul, kui ebaausaid kogumisneele on <N/3, vastasel korral on tõke <N/4. Culnane ja Schneideri teadetetahvlisüsteemist motiveeritult pakume välja uue süsteemi, mille korral on tagatud nii tõendatav püsivus kui ka tõendatav elusus, kui ebaausaid kogumisneele on vastavalt <N/3 ning <N/2. Lisaks on meie protokoll lihtne suhtluskeerukuselt. Antud töö põhineb konverentsile esitatud artiklil „A Cryptographic Approach to Bulletin Boards“ („Krüptograafiline lähenemine teadetetahvlisüsteemidele“), mille kaasautoriteks on Aggelos Kiayas, Helger Lipmaa, Janno Siim ja Thomas Zacharias.Vote collection together with storage of collected votes is the first phase of practically any electronic voting (e-voting) protocol. This functionality is provided by a bulletin board system. Many research papers in e-voting require the existence of a secure bulletin board, but there are only a few concrete systems. In the literature it is common to assume that bulletin board is a centralized trusted party, but in recent works the importance of a distributed fault-tolerant bulletin board has been raised. In this thesis, we propose a formal model for analysis of security and functionality of a bulletin board system motivated by the security requirements Culnane and Schneider introduced in Computer Security Foundations Symposium 2014. We consider a secure bulletin board as a robust public transaction ledger presented by Garay et al. in Eurocrypt 2015 that additionally provides receipts for successful postings. More precisely, we introduce two properties: (Confirmable) Persistence and Confirmable Liveness. We study a bulletin board system proposed by Culnane and Schneider in our model, and show that their protocol does not achieve Confirmable Liveness if there exist corrupted item collection peers, but achieves Confirmable Persistence for <N/3 corrupted item collection peers using only our trivial threshold signature scheme, otherwise the bound is <N/4. Motivated by the security analysis of Culnane-Schneider bulletin board system, we propose a fully secure bulletin board system and prove that it tolerates <N/3 corrupted item collection peers for Confirmable Persistence and <N/2 corrupted item collection peers for Confirmable Liveness. This thesis is based on a submitted paper "A Cryptographic Approach to Bulletin Boards" with co-authors Aggelos Kiayas, Helger Lipmaa, Janno Siim and Thomas Zacharias

Blockchain, consensus, and cryptography in electronic voting

Motivated by the recent trends to conduct electronic elections using blockchain technologies, we review the vast literature on cryptographic voting and assess the status of the field. We analyze the security requirements for voting systems and describe the major ideas behind the most influential cryptographic protocols for electronic voting. We focus on the great importance of consensus in the elimination of trusted third parties. Finally, we examine whether recent blockchain innovations can satisfy the strict requirements set for the security of electronic voting

Evolution of Bulletin Board & its application to E-Voting – A Survey

The voting process is fundamental to any democratic system – be it a country or a company\u27s boardroom. Nearly forty years ago, e-voting was theoretically perceived as a more efficient replacement of the widely existing paper-based traditional voting system. Several research works have been carried out to ensure more security and efficiency in different settings for e-voting schemes. One of the fundamental building blocks of e-voting systems is the public Bulletin Board through which several security properties are achieved. After introducing Blockchain technology, the bulletin board has found a new meaningful and concrete way of distributed way of implementation. Before Blockchain technology, either such a system was theoretically assumed or perceived as a public broadcast channel with memory. In this survey, we present a concise survey of bulletin boards\u27 evolution with a typical application to the e-voting systems. We note that bulletin boards have other applications in other joint computation areas. Still, we are interested in evolving e-voting systems based on bulletin board and how several desired security properties are realized through bulletin boards

A Distributed Bulletin Board Implementation for Practical Use in e­-Voting Systems

Tα σύγχρονα συστήματα ηλεκτρονικών ψηφοφοριών χτίζονται γύρω από έναν κεντρικοποιημένο, δημοσίως διαθέσιμο, ψηφιακό Πίνακα Ανακοινώσεων (ΠΑ). Όλα τα αντικείμενα που αναρτώνται στον ΠΑ είναι αυθεντικοποιημένα και δεν πρέπει κανένας να έχει τη δυνατότητα είτε να τα διαγράψει, είτε να τα τροποποιήσει. Ένας ΠΑ μπορεί να αποτελέσει ένα μοναδικό σημείο αποτυχίας ενός συστήματος. Για να αντιμετωπιστεί αυτό το κρίσιμο ζήτημα, μια σειρά από κατανεμημένες προσεγγίσεις έχουν προταθεί για την κατασκευή του ΠΑ. Γενικά, αυτές οι προτάσεις στερούνται είτε διαλειτουργικότητας, διότι είναι στενά συνδεδεμένες με συγκεκριμένα συστήματα ηλεκτρονικών ψηφοφοριών, είτε επιθεώρησης βάσει ενός επίσημου μοντέλου ασφαλείας. Στην παρούσα Διπλωματική Εργασία, ερευνούμε ένα σύνολο προτεινόμενων κατανεμημένων πρωτοκόλλων για ΠΑ, τα οποία δεν πάσχουν από τα προαναφερθέντα ελαττώματα, και αναλύουμε τις ιδιότητες ασφαλείας τους βάσει ενός συγκεκριμένου πλαισίου ασφαλείας. Η προτεινόμενη λύση μας αποτελείται από ένα ανεξάρτητο πλατφόρμας σύνολο δομοστοιχείων λογισμικού, τα οποία όχι μόνο υλοποιούν τα παραπάνω πρωτόκολλα, αλλά μπορούν και να εφαρμοστούν πάνω σε υπάρχοντα συστήματα ηλεκτρονικών ψηφοφοριών. Για την επικύρωση των ανωτέρω, ενσωματώνουμε τη λύση μας στο Zeus, ένα εδραιωμένο, επαληθεύσιμο, διαδικτυακό σύστημα κατάθεσης και καταμέτρησης ψηφοδελτίων. Επιπλέον, διατυπώνουμε βασικές πτυχές της υλοποίησης της προσέγγισής μας και επισημαίνουμε τις παραδοχές της προτεινόμενης λύσης. Στο τέλος, αξιολογούμε της ιδιότητες κλιμακωσιμότητας των ενσωματωμένων πρωτοκόλλων και παρέχουμε μία πειραματική ανάλυση ασφαλείας. Σε αυτήν, προσομοιώνουμε διαφορετικά σενάρια αντιπάλων και αξιολογούμε τις εγγυήσεις που παρέχει αυτή μας η υλοποίηση των πρωτοκόλλων για ΠΑ.Contemporary e-voting systems are built around a central, publicly accessible, digital Bulletin Board (BB). All items posted to a BB are authenticated and no entity should be able to either erase or modify them. However, the BB can be a potential single point of failure. To address this issue, a number of distributed approaches have been proposed for the make up of BBs. By and large, such proposals lack either interoperability as they are tied to specific e-voting systems or a review under a formal security model. In this thesis, we discuss a set of proposed distributed BB protocols that do not suffer from the above shortcomings and analyze their security properties based on a specific security framework. Our solution consists of a platform-independent set of modules that not only realize the above BB protocols but also can be applied on top of existing e-voting systems. As a proof of concept, we integrate our solution into Zeus, a well-established verifiable internet ballot casting and counting system. Moreover, we articulate key implementation aspects of our approach and underline the assumptions of our solution. Finally, we evaluate the scalability properties of the integrated protocols and provide an experimental security analysis. In this context, we simulate different adversarial scenarios and assess the guarantees that our realization of the BB protocols yields