Submitted by Aline Batista (alinehb.ufpel@gmail.com) on 2018-04-19T14:01:22Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_Rodrigo_Nuevo_Lellis.pdf: 1982046 bytes, checksum: 64712cc3d5117bfeff36f5d57b2f6054 (MD5) / Approved for entry into archive by Aline Batista (alinehb.ufpel@gmail.com) on 2018-04-19T14:41:57Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_Rodrigo_Nuevo_Lellis.pdf: 1982046 bytes, checksum: 64712cc3d5117bfeff36f5d57b2f6054 (MD5) / Made available in DSpace on 2018-04-19T14:45:19Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertacao_Rodrigo_Nuevo_Lellis.pdf: 1982046 bytes, checksum: 64712cc3d5117bfeff36f5d57b2f6054 (MD5) Previous issue date: 2017-02-23 / Sem bolsa / Nas últimas décadas uma das grandes preocupações de projetistas de hardware dedicado a aplicações que exigem segurança e sigilo de informações tais como smart cards são os ataques a canais laterais (em inglês Side Channel Attacks – SCAs). Estes ataques permitem relacionar os dados processados em dispositivos eletrônicos com grandezas físicas tais como a potência, a emissão de radiação eletromagnética ou o tempo de processamento. Isto se torna crítico quando, por exemplo, algoritmos criptográficos são executados e a chave criptográfica pode ser revelada pelo ataque. Dentre estes ataques, os baseados nos traços de potência, conhecidos como ataque por Análise Diferencial de Potência (em inglês Differential Power Analysis – DPA) e na emissão de radiação eletromagnética, denominados de Análise Diferencial Eletromagnética (em inglês Differential Electromagnetic Analysis - DEMA) são os mais populares, e por não serem invasivos, serem eficientes e não deixarem rastros no dispositivo atacado. Por outro lado, estes ataques exigem que a aquisição dos traços de potência ou radiação eletromagnética, sejam alinhados no tempo a fim de comparar e avaliar estatisticamente as amostras relativas a execução de operações com diferentes dados. Na literatura, existem diversas contramedidas visando evitar a ação destes ataques através da inserção de aleatoriedade de execução de operações, seja através da adição de atrasos aleatórios até a execução com diferentes frequências de relógio. Da mesma forma, existem propostas de estratégias baseadas em processamento de sinais aplicadas aos traços a fim de extrair informações vazadas pela arquitetura, métodos como correlação de fase (em inglês, Phase Only Correlation - POC), deformação dinâmica de tempo (do inglês, Dynamic Time Warping - DTW) e filtros digitais são usados em fluxos de ataques para estabelecer o realinhamento de traços antes da realização de ataques. Apesar disso, estes métodos são restritos a traços processados com sinal de relógio de mesma frequência ou com pequenas variações, o que por consequência exigem um grande número de traços e seus agrupamentos por frequência de operação. Este trabalho propõe um fluxo de ataque baseado no cálculo da energia dos traços a fim de permitir o realinhamento dos traços independentemente da frequência de operação e assim potencializar a ação dos ataques DPA em arquiteturas protegidas por contramedidas com inserção de aleatoriedade no processamento. Os resultados obtidos destacam que os ataques DPA são mais efetivos quando o cálculo da energia ocorre com segmentos de tamanho aproximado a metade do ciclo médio das frequências de operação dos traços atacados. Em comparação com trabalhos anteriores, o fluxo permite uma redução, no melhor caso, de aproximadamente 93% traços para um ataque bem-sucedido, motivando o uso do fluxo proposto. / In recent decades one of the major concerns of hardware designers dedicated to applications requiring security and secrecy of information such as smart cards are Side Channel Attacks (SCAs). These attacks allow you to relate processed data to electronic devices with physical quantities such as power consumption, electromagnetic radiation emission or processing time. This becomes critical when, for example, cryptographic algorithms are executed and the cryptographic key can be revealed by the attack. Among these attacks, by power consumption and emission of electromagnetic radiation are the most popular, known as Differential Power Analysis (DPA) and Differential Electromagnetic Analysis (DEMA). Since they are not invasive, efficient and leave no traces on the attacked device. These attacks require that the acquisition of traces of power consumption or electromagnetic radiation relating to the execution of cryptographic algorithms be time aligned in order to statistically compare and evaluate consumption or radiation samples for the execution of operations with different data. In the literature there are several countermeasures of these attacks through the randomization of execution operations either by adding random delays to the by changing clock frequencies. Similarly, there are proposals for strategies based on signal processing applied to the traces in order to extract information leaked by the architecture. Methods such as phase correlation (POC), dynamic time warping (DTW) and digital filters are used to realign traces before attacks. Nevertheless, these methods are restricted to traces processed with clock signal of the same frequency or with small variations, and require a large number of traces or their clustering frequency. This work proposes an attack flow based on the calculation of the trace energy in order to allow the realignment independently of the frequency of operation and thus enable the action of the DPA attacks in architectures with countermeasures based on processing randomization. Results show that DPA attacks are more effective when the energy is calculated in segments of approximately half the average cycle of the frequencies of operation of the traces attacked. Compared to previous works, the flow allows a reduction, in the best case, of approximately 93% traces for a successful attack, motivating the use of the proposed flow.

This master thesis explores how blockchain technologies can be utilized within the financial sector with focus on how to store both private and public information on the blockchain. The capital market is looking into ways of cutting down administrative work through streamlining the financial process by using blockchain technologies. Public key encryption together with hash functions and a consensus mechanism make up the basis for creating a shared trustless database system. The thesis was conducted by extensive research concerning cryptographic topics, and a literature study was made to compare existing solutions. This was done in order to come up with a new design which suggests how to utilize blockchain technologies in order to create private transactions. The design solves issues regarding key management and how to handle both private and public information on the blockchain. The proposed design is an extension of Visigon's existing permissioned blockchain, and it introduces different roles within the peer to peer network as well as a concept of having regulating nodes that together with the involved bank's nodes handle the process of private transactions. Private transactions are encrypted by using symmetric keys and thereafter recorded on the blockchain. In conclusion blockchain technology might not be the most suitable database system for banks to keep transactions private. Future solutions should consider the best attributes of blockchain technologies and create a new system with the single purpose of being a tool for the financial market.

Finnegan Lab System is a graphical computer program for learning how secret sharing works. With its focus on the algorithms and the data streams, the user does not have to consider machine-specific low-level details. It is highly modularised and is not restricted to secret sharing, but can easily be extended with new functions, such as building blocks for Feistel networks or signal processing. This thesis describes what secret sharing is, the development of a new lab system designed for secret sharing and how it can be used.

This is a study on the development of a re-authentication prototype. Re- authentication serves as a receipt for e.g. system administrators that authorise them to carry out a critical operation in a system that already is protected by a security architecture. A critical operation is a kind of operation that can cause serious damage to a network node or a set of network nodes, if it is done without one giving it a second thought. The purpose is to prevent mistakes and secure the users’ audit trail. The main task is to propose and implement a re-authentication prototype, that is to enable the incorporation of the re-authentication prototype to an already complete security architecture and yet preserve the security and performance level of the architecture. This thesis deals with this problem by using digitally signed certificates to provide the necessary security issues. The certificates used are called re- authentication certificates and follows the X.509 attribute certificate standard. The re-authentication certificate is optimised so that it only holds authorisation information regarding one critical operation. An access control decision function is used to decide if the re-authentication certificate and its owner are authentic. On basis of that decision the user can get the authority to execute critical operations. The finished prototype confirms that a re-authentication can be incorporated with the security architecture. The report also shows that the security status of the architecture is preserved. The performance of the prototype is rather difficult to prove since the prototype implementation only initialises the objects that are required to prove the security issues. A performance test can therefore never prove how the prototype will perform in an authentic environment. The performance is assumed to be adequate since it uses the same authentication function that is used by the security architecture.

Les problématiques de respect de la vie privée sont aujourd'hui indissociables des technologies modernes. Dans ce contexte, cette thèse s'intéresse plus particulièrement aux outils cryptographiques et à la façon de les utiliser pour répondre à ces nouvelles questions.Dans ce mémoire, je m'intéresserai tout d'abord aux preuves de connaissance sans divulgation qui permettent notamment d'obtenir la propriété d'anonymat pour les usagers de services de télécommunications. Je proposerai ainsi une nouvelle solution de preuve de connaissance d'un secret appartenant à un intervalle, ainsi que la première étude comparative des preuves existantes sur ce sujet. Je décrirai ensuite une nouvelle méthode permettant de vérifier efficacement un ensemble de preuves de type "Groth-Sahaï'', accélérant ainsi considérablement le travail du vérifieur pour de telles preuves. Dans un second temps, je m'intéresserai aux signatures caméléons. Celles-ci permettent de modifier, sous certaines conditions, un message signé. Ainsi, pour ces schémas, il est possible d'exhiber, à l'aide d'une trappe, une signature valide du signataire initial sur le message modifié. Je proposerai d'abord un nouveau schéma qui est à ce jour le plus efficace dans le modèle simple. Je m'intéresserai ensuite à certaines extensions de ce modèle qui ont pour vocation de donner au signataire les moyens de garder un certain contrôle sur les modifications faites a posteriori sur le message initial. Je décrirai ainsi à la fois le nouveau modèle de sécurité et les schémas associés prenant en compte ces nouvelles extensions. Enfin, je présenterai un ensemble d'applications se basant sur les briques cryptographiques introduites ci-dessus et qui permettent d'améliorer la protection de la vie privée des utilisateurs. J'aborderai tout particulièrement les problématiques d'abonnement, d'utilisation ou de facturation de services, ainsi que la gestion de contenus protégés dans un groupe hiérarchisé. / Privacy is, nowadays, inseparable from modern technology. This is the context in which the present thesis proposes new cryptographic tools to meet current challenges.Firstly, I will consider zero-knowledge proofs of knowledge, which allow in particular to reach the anonymity property. More precisely, I will propose a new range proof system and next give the first comparison between all existing solutions to this problem. Then, I will describe a new method to verify a set of ``Groth-Sahaï'' proofs, which significantly decreases the verification time for such proofs.In a second part, I will consider sanitizable signatures which allow, under some conditions, to manipulate (we say ``sanitize'') a signed message while keeping a valid signature of the initial signer. I will first propose a new scheme in the classical case. Next, I will introduce several extensions which enable the signer to obtain better control of the modifications done by the ``sanitizer''. In particular, I will propose a new security model taking into account these extensions and give different schemes achieving those new properties.Finally, I will present different applications of the above cryptographic tools that enhance customer privacy. In particular, I will consider the questions of subscription, use and billing of services and also address the issue of managing protected content in a hierarchical group.

Abstract In recent years, the amount of electronic communication has grown enormously. This has posed some new problems in information security. In particular, the methods in cryptography have been under much scrutiny. There are several basic primitives that modern cryptographic protocols utilise. One of these is hash functions, which are used to compute short hash values from messages of any length. In this thesis, we study the security of hash functions from two different viewpoints. First of all, we analyse the security of the Very Smooth Hash against preimage attacks. We develop an improved method for finding preimages of Very Smooth Hash, compare this method with existing methods and demonstrate its efficiency with practical results. Furthermore, we generalise this method to the discrete logarithm variants of the Very Smooth Hash. Secondly, we describe the methods for finding multicollisions in traditional iterated hash functions and give some extensions and improvements to these. We also outline a method for finding multicollisions for generalised iterated hash functions and discuss the implications of these findings. In addition, we generalise these multicollision finding methods to some graph-based hash functions. / Tiivistelmä Viime vuosina digitaaliseen tiedonsiirtoon perustuva tiedonsiirto on yleistynyt valtavasti. Tästä on seurannut monia uusia tietoturvaongelmia. Tässä yhteydessä erityisesti tiedon suojaamiseen käytetyt kryptografiset menetelmät ovat olleet tarkastelun kohteena. Hash-funktiot ovat yksi käytetyimmistä työkaluista nykyisissä kryptografisissa protokollissa. Tässä väitöskirjassa tarkastellaan hash-funktioiden turvallisuutta kahden eri tutkimusongelman kautta. Aluksi tutkitaan Very Smooth Hash -funktion turvallisuutta alkukuvien löytämistä vastaan. Alkukuvien löytämiseksi esitetään parannettu menetelmä, jota arvioidaan teoreettisilla ja käytännöllisillä menetelmillä. Tämä parannettu menetelmä yleistetään koskemaan myös Very Smooth Hashin muunnoksia, jotka perustuvat diskreetin logaritmin ongelmaan. Toisena tutkimuskohteena ovat iteroitujen hash-funktioiden yleistykset ja monitörmäykset. Aluksi esitellään perinteisiin iteroituihin hash-funktioihin liittyviä monitörmäysmenetelmiä. Tämän jälkeen tutkitaan iteroitujen hash-funktioiden yleistyksiä ja osoitetaan, että aiemmat monitörmäysmenetelmät voidaan laajentaa koskemaan myös näitä yleistyksiä. Lopuksi tutkitaan graafeihin perustuviin hash-funktioihin liittyviä monitörmäysmenetelmiä ja osoitetaan, että iteroitujen hash-funktioiden monitörmäysmenetelmä voidaan osittain yleistää koskemaan myös graafeihin perustuvia hash-funktioita.

Cette thèse a pour objet l'amélioration de la sécurité de systèmes à accès distant par l'utilisation d'outils cryptographiques. Elle s'applique en particulier aux applications de gestion de documents numériques pour leurs problématiques de communication, d'authentification et de gestion de droits. Contrairement aux approches classiques consistant à utiliser des moyens de protections ponctuels, nous proposons ici un ensemble d'outils conçu pour collaborer afin de renforcer la sécurité du système. La sécurisation des communications est réalisée grâce à la conception d'un protocole de communications sécurisée adapté aux applications distribuées. Les problématiques d'authentification ont donné lieu à l'élaboration de solutions permettant d'apporter un support cryptographique pour toutes modalités d'authentification. La gestion des droits fait l'objet d'un développement spécifique permettant d'associer des droits à des applications cryptographiques. Un point clé de ces réflexions est l'importance de l'accessibilité de ces outils de sécurité pour les utilisateurs du système. Cela a influé sur les propositions pour qu'elles perturbent le moins possible l'expérience utilisateur. Le résultat est l'intégration en un système global de différents outils et mécanismes apportant une sécurité complète à un système de gestion de documents numériques. Cette sécurité est basée sur des algorithmes cryptographiques afin de disposer de propriétés de sécurité prouvables et vérifiables. Comme support de ces mécanismes, une plate-forme de sécurité logicielle a été conçu pour fournir les outils cryptographiques de façon portable. / This thesis' goal is the improvement of the security of remotely accessed systems with the use of cryptographic tools. Specifically it is applied to digital documents management software that raise issues in three fields~: communication, authentication and rights management. Unlike common approaches that involve the use of individual protections for these three fields, we offer a set of tools made to work together to improve the system's security. Securing communication is done thanks to a new secure communication protocol designed for distributed applications. Authentication issues led to the development of two tailored solutions providing cryptographic support to the application for any authentication method. Rights management is handled through new associations between a given access right and specific cryptographic applications. A key element of those solutions is the emphasis put on the usability of these secure tools. It swayed the development of our proposals toward more transparent solutions that would not disturb the user experience. As a result, we obtained a secure system made of these tools and mechanisms that work together to provide full and transparent security for a digital documents management software. This security is fully based on cryptographic algorithms to provide provable and verifiable security properties. As a supporting layer for these mechanisms, a secure software library was designed to provide all the required tools for cryptographic uses in a portable way.

Please read the abstract in the section front of this document / Thesis (PhD)--University of Pretoria, 2009. / Electrical, Electronic and Computer Engineering / Unrestricted

The aim of this dissertation is to develop a new algorithm to embed a watermark in JPEG compressed images, using encoding methods. This encompasses the embedding of proprietary information, such as identity and authentication bitstrings, into the compressed material. This watermark encoding scheme involves combining entropy coding with homophonic coding, in order to embed a watermark in a JPEG image. Arithmetic coding was used as the entropy encoder for this scheme. It is often desired to obtain a robust digital watermarking method that does not distort the digital image, even if this implies that the image is slightly expanded in size before final compression. In this dissertation an algorithm that combines homophonic and arithmetic coding for JPEG images was developed and implemented in software. A detailed analysis of this algorithm is given and the compression (in number of bits) obtained when using the newly developed algorithm (homophonic and arithmetic coding). This research shows that homophonic coding can be used to embed a watermark in a JPEG image by using the watermark information for the selection of the homophones. The proposed algorithm can thus be viewed as a ‘key-less’ encryption technique, where an external bitstring is used as a ‘key’ and is embedded intrinsically into the message stream. The algorithm has achieved to create JPEG images with minimal distortion, with Peak Signal to Noise Ratios (PSNR) of above 35dB. The resulting increase in the entropy of the file is within the expected 2 bits per symbol. This research endeavor consequently provides a unique watermarking technique for images compressed using the JPEG standard. / Dissertation (MEng)--University of Pretoria, 2008. / Electrical, Electronic and Computer Engineering / unrestricted

L’avènement de l’ère digitale a changé la façon dont les individus communiquent à travers le monde, et a amené de nouvelles problématiques en terme de vie privée. La notion d’anonymat la plus répandue pour les communications sur Internet consiste à empêcher tout acteur du réseau de connaître à la fois l’expéditeur d’un message et son destinataire. Bien que ce niveau de protection soit adéquat pour l’utilisateur d’Internet moyen, il est insuffisant lorsqu’un individu peut être condamné pour le simple envoi de documents à une tierce partie. C’est le cas en particulier des lanceurs d’alerte, prenant des risques personnels pour informer le public de pratiques illégales ou antidémocratiques menées par de grandes organisations. Dans cette thèse, nous envisageons un niveau d’anonymat plus fort, où l’objectif est de dissimuler le fait même qu’un utilisateur envoie ou reçoive des données. Pour cela, nous délaissons l’architecture client-serveur couramment utilisée dans les réseaux anonymes, en faveur d’une architecture entièrement distribuée et homogène, où chaque utilisateur remplit également le rôle de serveur relai, lui permettant de dissimuler son propre trafic dans celui qu’il relai pour les autres. Dans cette optique, nous proposons un nouveau protocole pour les communications pairs à pairs sur Internet. À l’aide de récents outils de preuves cryptographiques, nous prouvons que ce protocole réalise les propriétés d’anonymat désirées. De plus, nous montrons par une étude pratique que, bien que le protocole induise une grande latence dans les communications, il assure un fort anonymat, même pour des réseaux de petite taille. / With the development of online communications in the past decades, new privacy concerns have emerged. A lot of research effort have been focusing on concealing relationships in Internet communications. However, most works do not prevent particular network actors from learning the original sender or the intended receiver of a communication. While this level of privacy is satisfactory for the common citizen, it is insufficient in contexts where individuals can be convicted for the mere sending of documents to a third party. This is the case for so-called whistle-blowers, who take personal risks to alert the public of anti-democratic or illegal actions performed by large organisations. In this thesis, we consider a stronger notion of anonymity for peer-to-peer communications on the Internet, and aim at concealing the very fact that users take part in communications. To this end, we deviate from the traditional client-server architecture endorsed by most existing anonymous networks, in favor of a homogeneous, fully distributed architecture in which every user also acts as a relay server, allowing it to conceal its own traffic in the traffic it relays for others. In this setting, we design an Internet overlay inspired from previous works, that also proposes new privacy-enhancing mechanisms, such as the use of relationship pseudonyms for managing identities. We formally prove with state-of-the-art cryptographic proof frameworks that this protocol achieves our privacy goals. Furthermore, a practical study of the protocol shows that it introduces high latency in the delivery of messages, but ensures a high anonymity level even for networks of small size.