Cryptographic Protocols for Privacy Enhancing Technologies: From Privacy Preserving Human Attestation to Internet Voting

Desire of privacy is oftentimes associated with the intention to hide certain aspects of our thoughts or actions due to some illicit activity. This is a narrow understanding of privacy, and a marginal fragment of the motivations for undertaking an action with a desired level of privacy. The right for not being subject to arbitrary interference of our privacy is part of the universal declaration of human rights (Article 12) and, above that, a requisite for our freedom. Developing as a person freely, which results in the development of society, requires actions to be done without a watchful eye. While the awareness of privacy in the context of modern technologies is not widely spread, it is clearly understood, as can be seen in the context of elections, that in order to make a free choice one needs to maintain its privacy. So why demand privacy when electing our government, but not when selecting our daily interests, books we read, sites we browse, or persons we encounter? It is popular belief that the data that we expose of ourselves would not be exploited if one is a law-abiding citizen. No further from the truth, as this data is used daily for commercial purposes: users’ data has value. To make matters worse, data has also been used for political purposes without the user’s consent or knowledge. However, the benefits that data can bring to individuals seem endless and a solution of not using this data at all seems extremist. Legislative efforts have tried, in the past years, to provide mechanisms for users to decide what is done with their data and define a framework where companies can use user data, but always under the consent of the latter. However, these attempts take time to take track, and have unfortunately not been very successful since their introduction. In this thesis we explore the possibility of constructing cryptographic protocols to provide a technical, rather than legislative, solution to the privacy problem. In particular we focus on two aspects of society: browsing and internet voting. These two events shape our lives in one way or another, and require high levels of privacy to provide a safe environment for humans to act upon them freely. However, these two problems have opposite solutions. On the one hand, elections are a well established event in society that has been around for millennia, and privacy and accountability are well rooted requirements for such events. This might be the reason why its digitalisation is something which is falling behind with respect to other acts of our society (banking, shopping, reading, etc). On the other hand, browsing is a recently introduced action, but that has quickly taken track given the amount of possibilities that it opens with such ease. We now have access to whatever we can imagine (except for voting) at the distance of a click. However, the data that we generate while browsing is extremely sensitive, and most of it is disclosed to third parties under the claims of making the user experience better (targeted recommendations, ads or bot-detection). Chapter 1 motivates why resolving such a problem is necessary for the progress of digital society. It then introduces the problem that this thesis aims to resolve, together with the methodology. In Chapter 2 we introduce some technical concepts used throughout the thesis. Similarly, we expose the state-of-the-art and its limitations. In Chapter 3 we focus on a mechanism to provide private browsing. In particular, we focus on how we can provide a safer, and more private way, for human attestation. Determining whether a user is a human or a bot is important for the survival of an online world. However, the existing mechanisms are either invasive or pose a burden to the user. We present a solution that is based on a machine learning model to distinguish between humans and bots that uses natural events of normal browsing (such as touch the screen of a phone) to make its prediction. To ensure that no private data leaves the user’s device, we evaluate such a model in the device rather than sending the data over the wire. To provide insurance that the expected model has been evaluated, the user’s device generates a cryptographic proof. However this opens an important question. Can we achieve a high level of accuracy without resulting in a noneffective battery consumption? We provide a positive answer to this question in this work, and show that a privacy-preserving solution can be achieved while maintaining the accuracy high and the user’s performance overhead low. In Chapter 4 we focus on the problem of internet voting. Internet voting means voting remotely, and therefore in an uncontrolled environment. This means that anyone can be voting under the supervision of a coercer, which makes the main goal of the protocols presented to be that of coercionresistance. We need to build a protocol that allows a voter to escape the act of coercion. We present two proposals with the main goal of providing a usable, and scalable coercion resistant protocol. They both have different trade-offs. On the one hand we provide a coercion resistance mechanism that results in linear filtering, but that provides a slightly weaker notion of coercion-resistance. Secondly, we present a mechanism with a slightly higher complexity (poly-logarithmic) but that instead provides a stronger notion of coercion resistance. Both solutions are based on a same idea: allowing the voter to cast several votes (such that only the last one is counted) in a way that cannot be determined by a coercer. Finally, in Chapter 5, we conclude the thesis, and expose how our results push one step further the state-of-the-art. We concisely expose our contributions, and describe clearly what are the next steps to follow. The results presented in this work argue against the two main claims against privacy preserving solutions: either that privacy is not practical or that higher levels of privacy result in lower levels of security.Programa de Doctorado en Ciencia y Tecnología Informática por la Universidad Carlos III de MadridPresidente: Agustín Martín Muñoz.- Secretario: José María de Fuentes García-Romero de Tejada.- Vocal: Alberto Peinado Domíngue

An Interoperable Access Control System based on Self-Sovereign Identities

The extreme growth of the World Wide Web in the last decade together with recent scandals related to theft or abusive use of personal information have left users unsatisfied withtheir digital identity providers and concerned about their online privacy. Self-SovereignIdentity (SSI) is a new identity management paradigm which gives back control over personal information to its rightful owner - the individual. However, adoption of SSI on theWeb is complicated by the high overhead costs for the service providers due to the lackinginteroperability of the various emerging SSI solutions. In this work, we propose an AccessControl System based on Self-Sovereign Identities with a semantically modelled AccessControl Logic. Our system relies on the Web Access Control authorization rules usedin the Solid project and extends them to additionally express requirements on VerifiableCredentials, i.e., digital credentials adhering to a standardized data model. Moreover,the system achieves interoperability across multiple DID Methods and types of VerifiableCredentials allowing for incremental extensibility of the supported SSI technologies bydesign. A Proof-of-Concept prototype is implemented and its performance as well as multiple system design choices are evaluated: The End-to-End latency of the authorizationprocess takes between 2-5 seconds depending on the used DID Methods and can theoretically be further optimized to 1.5-3 seconds. Evaluating the potential interoperabilityachieved by the system shows that multiple DID Methods and different types of VerifiableCredentials can be supported. Lastly, multiple approaches for modelling required Verifiable Credentials are compared and the suitability of the SHACL language for describingthe RDF graphs represented by the required Linked Data credentials is shown

Towards internet voting in the state of Qatar

Qatar is a small country in the Middle East which has used its oil wealth to invest in the country's infrastructure and education. The technology for Internet voting now exists or can be developed, but are the people of Qatar willing to take part in Internet voting for national elections?. This research identifies the willingness of government and citizens to introduce and participate in Internet voting (I-voting) in Qatar and the barriers that may be encountered when doing so. A secure I voting model for the Qatar government is then proposed that address issues of I-voting which might arise due to the introduction of such new technology. Recommendations are made for the Qatar government to assist in the introduction of I-voting. The research identifies the feasibility of I-voting and the government s readiness and willingness to introduce it. Multiple factors are examined: the voting experience, educational development, telecommunication development, the large number of Internet users, Qatar law which does not bar the use of I-voting and Qatar culture which supports I-voting introduction. It is shown that there is a willingness amongst both the people and the government to introduce I-voting, and there is appropriate accessibility, availability of IT infrastructure, availability of Internet law to protect online consumers and the existence of the e government project. However, many Qataris have concerns of security, privacy, usability, transparency and other issues that would need to be addressed before any voting system could be considered to be a quality system in the eyes of the voters. Also, the need to consider the security threat associated on client-side machines is identified where a lack of user awareness on information security is an important factor. The proposed model attempts to satisfy voting principles, introducing a secure platform for I-voting using best practices and solutions such as the smart card, Public Key Infrastructure (PKI) and digital certificates. The model was reviewed by a number of experts on Information Technology, and the Qatari culture and law who found that the system would, generally, satisfy voting principles, but pointed out the need to consider the scalability of the model, the possible cyber-attacks and the risks associated with voters computers. which could be reduced by enhancing user awareness on security and using secure operating systems or Internet browsers. From these findings, a set of recommendations were proposed to encourage the government to introduce I-voting which consider different aspects of I-voting, including the digital divide, e-literacy, I voting infrastructure, legal aspects, transparency, security and privacy. These recommendations were also reviewed by experts who found them to be both valuable and effective. Since literature on Internet voting in Qatar is sparse, empirical and non-empirical studies were carried out in a variety of surveys, interviews and experiments. The research successfully achieved its aim and objectives and is now being considered by the Qatari Government

Secret texts and cipherballots: secret suffrage and remote electronic voting

Una de les principals preocupacions sobre el vot telemàtic és com preservar el sufragi secret. La llista d’estudis que afirmen que el vot per Internet és incompatible amb el secret del vot és força extensa. Si bé estudis posteriors sobre experiències reals han tingut resultats més matisats, les preocupacions sobre el sufragi secret i el vot telemàtic es mantenen. Abordar aquestes preocupacions esdevé una obligació ineludible. En aquest context, la nostra recerca és novadora. En primer lloc, el nostre punt de partida no es basa en definicions legals preexistents que s'accepten com a donades. Partint de l'enfocament universalista del dret constitucional comparat, hem entès que el principi del sufragi secret transcendeix les opinions i convencions lligades a comunitats polítiques concretes. Aquesta concepció comú i bàsica s'ha traduït en tres estàndards: individualitat, confidencialitat i anonimat. Aquests estàndards s’han de satisfer en qualsevol canal de votació. En segon lloc, hem adoptat un enfocament més ampli en l’aplicació d’aquest principi al vot telemàtic. Hem demostrat que el sufragi secret es pot garantir mitjançant la llei, el codi informàtic, les normes i fins i tot el mercat. La normativa actual tendeix a ser limitada perquè recorre a analogies amb els canals de votació en paper i no reconeix les especificitats del vot telemàtic. Per contra, aquí hem examinat el paper que exerceixen (i les limitacions pròpies) del xifrat asimètric, l'anonimització basada en mix-nets o el recompte homomòrfic, i el vot múltiple.Una de las principales preocupaciones sobre el voto telemático es cómo garantizar el secreto del voto. La lista de autores que afirman que el voto por Internet es incompatible con el sufragio secreto es considerable. Aunque las conclusiones de estudios posteriores sobre experiencias reales hayan sido más matizadas, las preocupaciones sobre el sufragio secreto y el voto telemático se mantienen. Abordar estas preocupaciones constituye en una obligación ineludible. En este contexto, nuestra investigación es novedosa. En primer lugar, nuestro punto de partida no se basa en definiciones legales preexistentes que se aceptan como dadas. Partiendo del enfoque universalista del derecho constitucional comparado, hemos entendido que el principio del sufragio secreto trasciende las opiniones y convenciones ligadas a la cultura de comunidades políticas concretas. Esta concepción se ha traducido en tres normas: individualidad, confidencialidad y anonimato. Estas normas deberían aplicarse a cualquier canal de votación. En segundo lugar, hemos adoptado un enfoque más amplio sobre la aplicación de este principio. Hemos demostrado que el sufragio secreto puede garantizarse mediante la ley, el código, las normas e incluso el mercado. La normativa actual tiende a ser limitada porque recurre a analogías con los canales de votación en papel y no reconoce las especificidades del voto telemático.One of the key concerns about remote electronic voting is how to preserve secret suffrage. The list of authors who claim that Internet voting is incompatible with the secrecy of the vote is actually quite long. Even if later studies that analysed the actual implementation of remote electronic voting in public political elections had more nuanced findings, concerns about secret suffrage and remote electronic voting remain. Addressing these concerns becomes an inescapable obligation. In this context, our research is quite novel. First and foremost, our starting point is not based on pre-existing legal definitions that are accepted as given. Drawing from the universalist approach to comparative constitutional law, we have understood that the principle of secret suffrage exists in such a way that it transcends the culture bound opinions and conventions of particular political communities. This core understanding has been translated into three standards: individuality, confidentiality, and anonymity. These standards should apply to any voting channel. Second, we have taken a wider approach at the enforcement of this principle. We have showed that secret suffrage may be enforced through law, code, norms, and even the market. Current regulations tend to be constrained because they resort to analogies with paper-based voting channels and fail to acknowledge the specificities of remote electronic voting. In contrast, we have examined the role played by (and the limitations of) asymmetric encryption, anonymization based on mix-nets or homomorphic tallying, and of multiple voting to enforce secret suffrage

Election Reform and Electronic Voting Systems (DREs): Analysis of Security Issues

This report discusses several questions about voting-system security. To address these questions, this report begins with a description of the historical and policy context of the controversy. That is followed by an analysis of the issues in the broader context of computer security. The next section discusses several proposals that have been made for addressing those issues, and the last section discusses options for action that might be considered by policymakers

Applications of graph theory to wireless networks and opinion analysis

La teoría de grafos es una rama importante dentro de la matemática discreta. Su uso ha aumentado recientemente dada la conveniencia de los grafos para estructurar datos, para analizarlos y para generarlos a través de modelos. El objetivo de esta tesis es aplicar teoría de grafos a la optimización de redes inalámbricas y al análisis de opinión. El primer conjunto de contribuciones de esta tesis versa sobre la aplicación de teoría de grafos a redes inalámbricas. El rendimiento de estas redes depende de la correcta distribución de canales de frecuencia en un espacio compartido. Para optimizar estas redes se proponen diferentes técnicas, desde la aplicación de heurísticas como simulated annealing a la negociación automática. Cualquiera de estas técnicas requiere un modelo teórico de la red inalámbrica en cuestión. Nuestro modelo de redes Wi-Fi utiliza grafos geométricos para este propósito. Los vértices representan los dispositivos de la red, sean clientes o puntos de acceso, mientras que las aristas representan las señales entre dichos dispositivos. Estos grafos son de tipo geométrico, por lo que los vértices tienen posición en el espacio, y las aristas tienen longitud. Con esta estructura y la aplicación de un modelo de propagación y de uso, podemos simular redes inalámbricas y contribuir a su optimización. Usando dicho modelo basado en grafos, hemos estudiado el efecto de la interferencia cocanal en redes Wi-Fi 4 y mostramos una mejora de rendimiento asociada a la técnica de channel bonding cuando se usa en regiones donde hay por lo menos 13 canales disponibles. Por otra parte, en esta tesis doctoral hemos aplicado teoría de grafos al análisis de opinión dentro de la línea de investigación de SensoGraph, un método con el que se realiza un análisis de opinión sobre un conjunto de elementos usando grafos de proximidad, lo que permite manejar grandes conjuntos de datos. Además, hemos desarrollado un método de análisis de opinión que emplea la asignación manual de aristas y distancias en un grafo para estudiar la similaridad entre las muestras dos a dos. Adicionalmente, se han explorado otros temas sin relación con los grafos, pero que entran dentro de la aplicación de las matemáticas a un problema de la ingeniería telemática. Se ha desarrollado un sistema de votación electrónica basado en mixnets, secreto compartido de Shamir y cuerpos finitos. Dicha propuesta ofrece un sistema de verificación numérico novedoso a la vez que mantiene las propiedades esenciales de los sistemas de votación

Voting Technology and the Quest for Trustworthy Elections

This chapter reviews four dimensions of the still-unresolved voting technology quandary. It begins by briefly reviewing the Florida Bush v. Gore background that, combined with the tradition of state governmental control over election administration, spawned the contours and limitations of new federal regulatory apparatus. It also surveys some illustrative voting system malfunctions and their consequences surfacing predominantly from 2009–12. The second part of this chapter, Federal Compulsion to Adopt Software-Based Voting Technologies, explains the misconceptions about software and digital equipment that led to both the flawed federal mandates and the ineffectual regulatory structure. The third part of this chapter, Litigation and Enforcement Strategies, focuses primarily on the curious omission of Federal enforcement of HAVA\u27s voting technology standards. This part also considers private party litigation that has sought to invalidate the use of allegedly defective voting machines. The final part of this chapter examines Federal Promotion of Problematic Internet Voting. The chapter concludes by advancing recommendations for preparing the legal system to realize voting rights despite the wide deployment of problematic voting technologies

Voting Technology and the Quest for Trustworthy Elections

This chapter reviews four dimensions of the still-unresolved voting technology quandary. It begins by briefly reviewing the Florida Bush v. Gore background that, combined with the tradition of state governmental control over election administration, spawned the contours and limitations of new federal regulatory apparatus. It also surveys some illustrative voting system malfunctions and their consequences surfacing predominantly from 2009–12. The second part of this chapter, Federal Compulsion to Adopt Software-Based Voting Technologies, explains the misconceptions about software and digital equipment that led to both the flawed federal mandates and the ineffectual regulatory structure. The third part of this chapter, Litigation and Enforcement Strategies, focuses primarily on the curious omission of Federal enforcement of HAVA\u27s voting technology standards. This part also considers private party litigation that has sought to invalidate the use of allegedly defective voting machines. The final part of this chapter examines Federal Promotion of Problematic Internet Voting. The chapter concludes by advancing recommendations for preparing the legal system to realize voting rights despite the wide deployment of problematic voting technologies

From Information Theory Puzzles in Deletion Channels to Deniability in Quantum Cryptography

Research questions, originally rooted in quantum key exchange (QKE), have branched off into independent lines of inquiry ranging from information theory to fundamental physics. In a similar vein, the first part of this thesis is dedicated to information theory problems in deletion channels that arose in the context of QKE. From the output produced by a memoryless deletion channel with a uniformly random input of known length n, one obtains a posterior distribution on the channel input. The difference between the Shannon entropy of this distribution and that of the uniform prior measures the amount of information about the channel input which is conveyed by the output of length m. We first conjecture on the basis of experimental data that the entropy of the posterior is minimized by the constant strings 000..., 111... and maximized by the alternating strings 0101..., 1010.... Among other things, we derive analytic expressions for minimal entropy and propose alternative approaches for tackling the entropy extremization problem. We address a series of closely related combinatorial problems involving binary (sub/super)-sequences and prove the original minimal entropy conjecture for the special cases of single and double deletions using clustering techniques and a run-length encoding of strings. The entropy analysis culminates in a fundamental characterization of the extremal entropic cases in terms of the distribution of embeddings. We confirm the minimization conjecture in the asymptotic limit using results from hidden word statistics by showing how the analytic-combinatorial methods of Flajolet, Szpankowski and Vallée, relying on generating functions, can be applied to resolve the case of fixed output length and n → ∞. In the second part, we revisit the notion of deniability in QKE, a topic that remains largely unexplored. In a work by Donald Beaver it is argued that QKE protocols are not necessarily deniable due to an eavesdropping attack that limits key equivocation. We provide more insight into the nature of this attack and discuss how it extends to other prepare-and-measure QKE schemes such as QKE obtained from uncloneable encryption. We adopt the framework for quantum authenticated key exchange developed by Mosca et al. and extend it to introduce the notion of coercer-deniable QKE, formalized in terms of the indistinguishability of real and fake coercer views. We also elaborate on the differences between our model and the standard simulation-based definition of deniable key exchange in the classical setting. We establish a connection between the concept of covert communication and deniability by applying results from a work by Arrazola and Scarani on obtaining covert quantum communication and covert QKE to propose a simple construction for coercer-deniable QKE. We prove the deniability of this scheme via a reduction to the security of covert QKE. We relate deniability to fundamental concepts in quantum information theory and suggest a generic approach based on entanglement distillation for achieving information-theoretic deniability, followed by an analysis of other closely related results such as the relation between the impossibility of unconditionally secure quantum bit commitment and deniability. Finally, we present an efficient coercion-resistant and quantum-secure voting scheme, based on fully homomorphic encryption (FHE) and recent advances in various FHE primitives such as hashing, zero-knowledge proofs of correct decryption, verifiable shuffles and threshold FHE