Tamper-proof secret image-sharing scheme for identifying cheated secret keys and shared images

[[abstract]]A (t,n) secret image-sharing scheme shares a secret image to n participants, and the t users recover the image. During the recovery procedure of a conventional secret image-sharing scheme, cheaters may use counterfeit secret keys or modified shared images to cheat other users’ secret keys and shared images. A cheated secret key or shared image leads to an incorrect secret image. Unfortunately, the cheater cannot be identified. We present an exponent and modulus-based scheme to provide a tamper-proof secret image-sharing scheme for identifying cheaters on secret keys or shared images. The proposed scheme allows users to securely select their secret key. This assignment can be performed over networks. Modulus results of each shared image is calculated to recognize cheaters of a shared image. Experimental results indicate that the proposed scheme is excellent at identifying cheated secret keys and shared images.[[incitationindex]]SCI[[booktype]]紙本[[booktype]]電子

Abordando fatores humanos no projeto de soluções criptográficas : dois estudos de caso em validação de itens e autenticação

Orientador: Ricardo DahabTese (doutorado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: O projeto de soluções criptográficas seguras a partir de uma perspectiva puramente teórica não é suficiente para garantir seu sucesso em cenários realistas. Diversas vezes, as premissas sob as quais estas soluções são propostas não poderiam estar mais longe das necessidades do mundo real. Um aspecto frequentemente esquecido, que pode influenciar em como a solução se sai ao ser integrada, é a forma como o usuário final interage com ela (i.e., fatores humanos). Neste trabalho, estudamos este problema através da análise de dois cenários de aplicação bem conhecidos da pesquisa em Segurança da Informação: O comércio eletrônico de itens digitais e Internet banking. Protocolos de trocas justas tem sido amplamente estudados, mas continuam não sendo implementados na maioria das transações de comércio eletrônico disponíveis. Para diversos tipos de itens digitais (e-goods), o modelo de negócios atual para comércio eletrônico falha em garantir justiça aos clientes. A validação de itens é um passo crítico em trocas justas, e recebeu pouca atenção dos pesquisadores. Nós acreditamos que estes problemas devam ser abordados de forma integrada, para que os protocolos de trocas justas possam ser efetivamente implementados no mercado. De forma geral, acreditamos também que isso seja um reflexo de paradigmas de projeto orientado a sistemas para soluções de segurança, que são centrados em dados em vez de usuários, o que resulta em métodos e técnicas que frequentemente desconsideram os requisitos de usuários. Contextualizamos como, ao subestimar as sutilezas do problema da validação de itens, o modelo atual para compra e venda de itens digitais falha em garantir sucesso, na perspectiva dos compradores, para as transações ¿ sendo, portanto, injusto por definição. Também introduzimos o conceito de Degradação Reversível, um método que inerentemente inclui o passo de validação de itens em transações de compra e venda com a finalidade de mitigar os problemas apresentados. Como prova-de-conceito, produzimos uma implementação de Degradação Reversível baseada em códigos corretores de erros sistemáticos (SECCs), destinada a conteúdo multimídia. Este método é também o subproduto de uma tentativa de incluir os requisitos do usuário no processo de construção de métodos criptográficos, uma abordagem que, em seguida, evoluímos para o denominado projeto de protocolos orientado a itens. De uma perspectiva semelhante, também propomos um método inovador para a autenticação de usuários e de transações para cenários de Internet Banking. O método proposto, baseado em Criptografia Visual, leva em conta tanto requisitos técnicos quanto de usuário, e cabe como um componente seguro ¿ e intuitivo ¿ para cenários práticos de autenticação de transaçõesAbstract: Designing secure cryptographic solutions from a purely theoretical perspective is not enough to guarantee their success in a realistic scenario. Many times, the assumptions under which these solutions are designed could not be further from real-world necessities. One particular, often-overlooked aspect that may impact how the solution performs after deployment is how the final user interacts with it (i.e., human factors). In this work, we take a deeper look into this issue by analyzing two well known application scenarios from Information Security research: The electronic commerce of digital items and Internet banking. Fair exchange protocols have been widely studied, but are still not implemented on most e-commerce transactions available. For several types of digital items (e-goods), the current e-commerce business model fails to provide fairness to customers. A critical step in fair exchange is item validation, which still lacks proper attention from researchers. We believe this issue should be addressed in a comprehensive and integrated fashion before fair exchange protocols can be effectively deployed in the marketplace. More generally, we also believe this to be the consequence of ongoing system-oriented security solution design paradigms that are data-centered, as opposed to user-centered, thus leading to methods and techniques that often disregard users¿ requirements. We contextualize how, by overlooking the subtleties of the item validation problem, the current model for buying and selling digital items fails to provide guarantees of a successful transaction outcome to customers, thus being unfair by design. We also introduce the concept of Reversible Degradation, a method for enhancing buy-sell transactions concerning digital items that inherently includes the item validation step in the purchase protocol in order to tackle the discussed problems. As a proof-of-concept, we produce a deliverable instantiation of Reversible Degradation based on systematic error correction codes (SECCs), suitable for multimedia content. This method is also the byproduct of an attempt to include users¿ requirements into the cryptographic method construction process, an approach that we further develop into a so-called item-aware protocol design. From a similar perspective, we also propose a novel method for user and transaction authentication for Internet Banking scenarios. The proposed method, which uses Visual Cryptography, takes both technical and user requirements into account, and is suitable as a secure ¿ yet intuitive ¿ component for practical transaction authentication scenariosDoutoradoCiência da ComputaçãoDoutor em Ciência da Computaçã

Election Security Is Harder Than You Think

Recent years have seen the rise of nation-state interference in elections across the globe, making the ever-present need for more secure elections all the more dire. While certain common-sense approaches have been a typical response in the past, e.g. ``don't connect voting machines to the Internet'' and ``use a voting system with a paper trail'', known-good solutions to improving election security have languished in relative obscurity for decades. These techniques are only now finally being implemented at scale, and that implementation has brought the intricacies of sophisticated approaches to election security into full relief. This dissertation argues that while approaches to improve election security like paper ballots and post-election audits seem straightforward, in reality there are significant practical barriers to sufficient implementation. Overcoming these barriers is a necessary condition for an election to be secure, and while doing so is possible, it requires significant refinement of existing techniques. In order to better understand how election security technology can be improved, I first develop what it means for an election to be secure. I then delve into experimental results regarding voter-verified paper, discussing the challenges presented by paper ballots as well as some strategies to improve the security they can deliver. I examine the post-election audit ecosystem and propose a manifest improvement to audit workload analysis through parallelization. Finally, I show that even when all of these conditions are met (as in a vote-by-mail scenario), there are still wrinkles that must be addressed for an election to be truly secure.PHDComputer Science & EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/163272/1/matber_1.pd

Cryptographic techniques for privacy and access control in cloud-based applications

Digitization is one of the key challenges for today’s industries and society. It affects more and more business areas and also user data and, in particular, sensitive information. Due to its sensitivity, it is important to treat personal information as secure and private as possible yet enabling cloud-based software to use that information when requested by the user. In this thesis, we focus on the privacy-preserving outsourcing and sharing of data, the querying of outsourced protected data, and the usage of personal information as an access control mechanism for rating platforms, which should be protected from coercion attacks. In those three categories, we present cryptographic techniques and protocols that push the state of the art. In particular, we first present multi-client oblivious RAM (ORAM), which augments standard ORAM with selective data sharing through access control, confidentiality, and integrity. Second, we investigate on recent work in frequency-hiding order-preserving encryption and show that the state of the art misses rigorous treatment, allowing for simple attacks against the security of the existing scheme. As a remedy, we show how to fix the security definition and that the existing scheme, slightly adapted, fulfills it. Finally, we design and develop a coercion-resistant rating platform. Coercion-resistance has been dealt with mainly in the context of electronic voting yet also affects other areas of digital life such as rating platforms.Die Digitalisierung ist eine der größten Herausforderungen für Industrie und Gesellschaft. Neben vielen Geschäftsbereichen betrifft diese auch, insbesondere sensible, Nutzerdaten. Daher sollten persönliche Informationen so gut wie möglich gesichert werden. Zugleich brauchen Cloud-basierte Software-Anwendungen, die der Nutzer verwenden möchte, Zugang zu diesen Daten. Diese Dissertation fokussiert sich auf das sichere Auslagern und Teilen von Daten unter Wahrung der Privatsphäre, auf das Abfragen von geschützten, ausgelagerten Daten und auf die Nutzung persönlicher Informationen als Zugangsberechtigung für erpressungsresistente Bewertungsplattformen. Zu diesen drei Themen präsentieren wir kryptographische Techniken und Protokolle, die den Stand der Technik voran treiben. Der erste Teil stellt Multi-Client Oblivious RAM (ORAM) vor, das ORAM durch die Möglichkeit, Daten unter Wahrung von Vertraulichkeit und Integrität mit anderen Nutzern zu teilen, erweitert. Der zweite Teil befasst sich mit Freuquency-hiding Order-preserving Encryption. Wir zeigen, dass dem Stand der Technik eine formale Betrachtung fehlt, was zu Angriffen führt. Um Abhilfe zu schaffen, verbessern wir die Sicherheitsdefinition und beweisen, dass das existierende Verschlüsselungsschema diese durch minimale Änderung erfüllt. Abschließend entwickeln wir ein erpressungsresistentes Bewertungsportal. Erpressungsresistenz wurde bisher hauptsächlich im Kontext von elektronischen Wahlen betrachtet

Individual verifiability in electronic voting

This PhD Thesis is the fruit of the job of the author as a researcher at Scytl Secure Electronic Voting, as well as the collaboration with Paz Morillo, from the Department of Applied Mathematics at UPC and Alex Escala, PhD student. In her job at Scytl, the author has participated in several electronic voting projects for national-level binding elections in different countries. The participation of the author covered from the protocol design phase, to the implementation phase by providing support to the development teams. The thesis focuses on studying the mechanisms that can be provided to the voters, in order to examine and verify the processes executed in a remote electronic voting system. This work has been done as part of the tasks of the author at the electronic voting company Scytl. Although this thesis does not talk about system implementations, which are interesting by themselves, it is indeed focused on protocols which have had, or may have, an application in the real world. Therefore, it may surprise the reader by not using state of the art cryptography such as pairings or lattices, which still, although providing very interesting properties, cannot be efficiently implemented and used in a real system. Otherwise, the protocols presented in this thesis use standard and well-known cryptographic primitives, while providing new functionalities that can be applied in nowadays electronic voting systems. The thesis has the following contents: A survey on electronic voting systems which provide voter verification functionalities. Among these systems we can find the one used in the Municipal and Parliamentary Norwegian elections of 2011 and 2013, and the system used in the Australian State of New South Wales for the General State Elections in 2015, in which the author has had an active participation in the design of their electronic voting protocols. A syntax which can be used for modeling electronic voting systems providing voter verifiability. This syntax is focused on systems characterized by the voter confirming the casting of her vote, after verifying some evidences provided by the protocol. Along with this syntax, definitions for the security properties required for such schemes are provided. A description of the electronic voting protocol and system which has been used in 2014 and 2015 elections in the Swiss Canton of Neuchâtel, which has individual verification functionalities, is also provided in this thesis, together with a formal analysis of the security properties of the scheme and further extensions of the protocol. Finally, two new protocols which provide new functionalities respect to those from the state of the art are proposed: A new protocol providing individual verifiability which allows voters to defend against coertion by generating fake proofs, and a protocol which makes a twist to individual verifiability by ensuring that all the processes executed by the voting device and the remote server are correct, without requiring an active verification from the voter. A formal analysis of the security properties of both protocols is provided, together with examples of implementation in real systems.Aquesta tesi és fruit de la feina de l'autora com a personal de recerca a la empresa Scytl Secure Electtronic Voting, així com de la col·laboració amb la Paz Morillo, del departament de matemàtica aplicada a la UPC, i el Alex Escala, estudiant de doctorat. A la feina a Scytl, l'autora ha participat a varis projectes de vot electrònic per a eleccions vinculants a nivell nacional, que s'han efectuat a varis països. La participació de la autora ha cobert tant la fase de disseny del protocol, com la fase de implementació, on ha proveït suport als equips de desenvolupament. La tesi estudia els mecanismes que es poden proporcionar als votants per a poder examinar i verificar els processos que s'executen en sistemes de vot electrònic. Tot i que la tesi no parla de la implementació dels sistemes de vot electrònic, sí que s'enfoca en protocols que han tingut, o poden tenir, una aplicació pràctica actualment. La tesi té els continguts següents: Un estudi en sistemes de vot electrònic que proporcionen funcionalitats per a que els votants verifiquin els processos. Entre aquests sistemes, trobem el que es va utilitzar a les eleccions municipals i parlamentàries a Noruega als anys 2011 i 2013, així com el sistema utilitzat a l'estat Australià de New South Wales, per a les eleccions generals de 2015, sistemes en els que l'autora ha participat directament en el diseny dels seus protocols criptogràfics. La tesi també conté una sintaxi que es pot utilizar per modelar sistemes de vot electrònic que proporcionen verificabilitat individual (on verifica el votant). Aquesta sintaxi s'enfoca en sistemes caracteritzats pel fet de que el votant confirma la emissió del seu vot un cop ha verificat unes evidències sobre ell, proporcionades pel protocol. A més de la sintaxi, es proporcionen definicions de les propietats de seguretat d'aquestts sistemes. La tesi també conté una descripció del sistema i protocol de vot electrònic que s'utilitza al cantó Suís de Neuchâtel a partir del 2014, el qual té funcionalitats per a que els votants verifiquin certs processos del sistema. La tesi a més conté un anàlisi de la seguretat de l'esquema, així com possibles extensions del protocol. Finalment, la tesi inclou dos protocols nous que proporcionen noves característiques i funcionalitats respecte als existents a l'estat de l'art de la tècnica. El primer permet a un votant defendre's de un coaccionador generant proves falses, i el segon fa un canvi de paradigma de la verificabilitat individual, de forma que el votant no ha de verificar certs processos per a saber que s'han efectuant correctament. La tesi inclou un anàlisi formal de les propietats de seguretat dels dos protocols, així com exemples de com podrien ser implementats en un escenari real.Postprint (published version

Secure fingerprinting on sound foundations

The rapid development and the advancement of digital technologies open a variety of opportunities to consumers and content providers for using and trading digital goods. In this context, particularly the Internet has gained a major ground as a worldwiede platform for exchanging and distributing digital goods. Beside all its possibilities and advantages digital technology can be misuesd to breach copyright regulations: unauthorized use and illegal distribution of intellectual property cause authors and content providers considerable loss. Protections of intellectual property has therefore become one of the major challenges of our information society. Fingerprinting is a key technology in copyright protection of intellectual property. Its goal is to deter people from copyright violation by allowing to provably identify the source of illegally copied and redistributed content. As one of its focuses, this thesis considers the design and construction of various fingerprinting schemes and presents the first explicit, secure and reasonably efficient construction for a fingerprinting scheme which fulfills advanced security requirements such as collusion-tolerance, asymmetry, anonymity and direct non-repudiation. Crucial for the security of such s is a careful study of the underlying cryptographic assumptions. In case of the fingerprinting scheme presented here, these are mainly assumptions related to discrete logarithms. The study and analysis of these assumptions is a further focus of this thesis. Based on the first thorough classification of assumptions related to discrete logarithms, this thesis gives novel insights into the relations between these assumptions. In particular, depending on the underlying probability space we present new reuslts on the reducibility between some of these assumptions as well as on their reduction efficency.Die Fortschritte im Bereich der Digitaltechnologien bieten Konsumenten, Urhebern und Anbietern große Potentiale für innovative Geschäftsmodelle zum Handel mit digitalen Gütern und zu deren Nutzung. Das Internet stellt hierbei eine interessante Möglichkeit zum Austausch und zur Verbreitung digitaler Güter dar. Neben vielen Vorteilen kann die Digitaltechnik jedoch auch missbräuchlich eingesetzt werden, wie beispielsweise zur Verletzung von Urheberrechten durch illegale Nutzung und Verbreitung von Inhalten, wodurch involvierten Parteien erhebliche Schäden entstehen können. Der Schutz des geistigen Eigentums hat sich deshalb zu einer der besonderen Herausforderungen unseres Digitalzeitalters entwickelt. Fingerprinting ist eine Schlüsseltechnologie zum Urheberschutz. Sie hat das Ziel, vor illegaler Vervielfältigung und Verteilung digitaler Werke abzuschrecken, indem sie die Identifikation eines Betrügers und das Nachweisen seines Fehlverhaltens ermöglicht. Diese Dissertation liefert als eines ihrer Ergebnisse die erste explizite, sichere und effiziente Konstruktion, welche die Berücksichtigung besonders fortgeschrittener Sicherheitseigenschaften wie Kollusionstoleranz, Asymmetrie, Anonymität und direkte Unabstreitbarkeit erlaubt. Entscheidend für die Sicherheit kryptographischer Systeme ist die präzise Analyse der ihnen zugrunde liegenden kryptographischen Annahmen. Den im Rahmen dieser Dissertation konstruierten Fingerprintingsystemen liegen hauptsächlich kryptographische Annahmen zugrunde, welche auf diskreten Logarithmen basieren. Die Untersuchung dieser Annahmen stellt einen weiteren Schwerpunkt dieser Dissertation dar. Basierend auf einer hier erstmals in der Literatur vorgenommenen Klassifikation dieser Annahmen werden neue und weitreichende Kenntnisse über deren Zusammenhänge gewonnen. Insbesondere werden, in Abhängigkeit von dem zugrunde liegenden Wahrscheinlichkeitsraum, neue Resultate hinsichtlich der Reduzierbarkeit dieser Annahmen und ihrer Reduktionseffizienz erzielt

Privacy-aware Biometric Blockchain based e-Passport System for Automatic Border Control

In the middle of 1990s, World Wide Web technology initially steps into our life. Now, 30 years after that, widespread internet access and established computing technology bring embodied real life into Metaverse by digital twin. Internet is not only blurring the concept of physical distance, but also blurring the edge between the real and virtual world. Another breakthrough in computing is the blockchain, which shifts the root of trust attached to a system administrator to the computational power of the system. Furthermore, its favourable properties such as immutable time-stamped transaction history and atomic smart contracts trigger the development of decentralized autonomous organizations (DAOs). Combining above two, this thesis presents a privacy-aware biometric Blockchain based e-passport system for automatic border control(ABC), which aims for improving the efficiency of existing ABC system. Specifically, through constructing a border control Metaverse DAO, border control workload can be autonomously self-executed by atomic smart contracts as transaction and then immutably recorded on Blockchain. What is more, to digitize border crossing documentation, biometric Blockchain based e-passport system(BBCVID) is created to generate an immutable real-world identity digital twin in the border control Metaverse DAO through Blockchain and biometric identity authentication. That is to say, by digitizing border crossing documentation and automatizing both biometric identity authentication and border crossing documentation verification, our proposal is able to significantly improve existing border control efficiency. Through system simulation and performance evaluation by Hyperledger Caliper, the proposed system turns out to be able to improve existing border control efficiency by 3.5 times more on average, which is remarkable. What is more, the dynamic digital twin constructed by BBCVID enables computing techniques such as machine learning and big data analysis applicable to real-world entity, which has a huge potential to create more value by constructing smarter ABC systems

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