Le contexte particulier du dopage suscite de nombreuses questions à l'égard des obligations et de la responsabilité des médecins. Suivant le Code médical du Mouvement olympique (2005), les médecins doivent respecter les principes de l'éthique médicale et ceux de l'éthique sportive, comme le fairplay. Il arrive parfois que l'éthique sportive entre en conflit avec l'éthique médicale. Les médecins sont alors confrontés à d'importants dilemmes qui peuvent engager leur responsabilité professionnelle et civile. Ces dilemmes se situent notamment au niveau de l'obligation de soins et du secret professionnel. Par exemple, les médecins peuvent-ils prescrire des médicaments pour contrer les effets néfastes du dopage afin de préserver la santé des athlètes ? La question de la recherche sur l'amélioration de la performance est également préoccupante. En raison du caractère clandestin de cette recherche, il y a lieu de se demander si les médecins qui y participent respectent leurs obligations professionnelles. L'analyse des principaux instruments normatifs applicables en l'espèce démontre que les médecins ne doivent pas être placés dans une situation telle qu'ils doivent refuser de suivre des athlètes de crainte d'être accusés de dopage. De plus, le secret professionnel devrait être maintenu lorsqu'un médecin suit un athlète dopé afin de préserver la relation de confiance. Finalement, l'analyse du contexte de la recherche portant sur l'amélioration de la performance révèle que les médecins ne respectent pas toujours leurs obligations. Les médecins fautifs risquent donc d'engager leur responsabilité professionnelle et civile et de faire face à des sanctions sévères. / The particular context of doping raises many questions regarding the obligations and the liability of physicians. According to the Medical Code of the Olympic Movement (2005), physicians must respect the principles of medical ethics as well as those of sport ethics, such as fair play. Sometimes, sport ethics conflicts with medical ethics. Therefore, physicians are confronted with important dilemmas, which could engage their professional and civil liability. These dilemmas concern, in particular, the duty of care and professional secrecy. For example, could physicians prescribe drugs to counter the side effects of doping in order to preserve the health of the athletes? Issues surrounding research on the improvement of performance is also of interest. Because of the often clandestine nature of this research, it should be asked whether physicians who participate respect their professional obligations. An analysis of the principal normative documents applicable demonstrates that physicians should not be placed in a situation where they would refuse to treat athletes because of fear of accusations of doping. Moreover, professional secrecy should be maintained when a physician follows an athlete in order to preserve the relation of trust. Finally, the analysis of the context of the research on the improvement of performance reveals that physicians don't always respect their obligations. These physicians might engage their professional and civil liability and face severe sanctions.

Based on the considerations presented by the Constitutional Court in the light of a specific case, this article addresses the discussion about the limit of intervention that the employer has to intercept and collect those communications that are protected by the secrecy of the law of the Communications of workers, establishing the possibility of implementing new control mechanisms that suspend any kind of expectation of confidentiality. / A partir de las consideraciones expuestas por el Tribunal Constitucional en atención a un caso en concreto, el presente artículo aborda la discusión sobre el límite de intervención que posee el empleador para interceptar y recaudar aquellas comunicaciones que se encuentran protegidas por el secreto al derecho de las comunicaciones de los trabajadores, estableciendo la posibilidad de implementar nuevos mecanismos de control que suspenden cualquier tipo de expectativa de confidencialidad.

Redundancy in plaintext is a fertile source of attack in any encryption system. Compression before encryption reduces the redundancy in the plaintext, but this does not make a cipher more secure. The cipher text is still susceptible to known-plaintext and chosen-plaintext attacks. The aim of homophonic coding is to convert a plaintext source into a random sequence by randomly mapping each source symbol into one of a set of homophones. Each homophone is then encoded by a source coder after which it can be encrypted with a cryptographic system. The security of homophonic coding falls into the class of unconditionally secure ciphers. The main advantage of homophonic coding over pure source coding is that it provides security both against known-plaintext and chosen-plaintext attacks, whereas source coding merely protects against a ciphertext-only attack. The aim of this dissertation is to investigate the implementation of an adaptive homophonic coder based on an arithmetic coder. This type of homophonic coding is termed universal, as it is not dependent on the source statistics. / Computer Science / M.Sc. (Computer Science)

Smart grids representam o futuro das redes elétricas. Estes tipos de redes devem ser robustas a flutuações de carga e devem possuir monitoramento e gerenciamento inteligente e em tempo real. Para que essas demandas sejam possíveis, é preciso uma comunicação de dados de alta velocidade, flexível e de baixo custo. Dentro dessas características, muitos autores propõem a utilização de sistemas de comunicação sem fio, os quais possuem um custo de implantação mais baixo que redes ópticas ou cabeadas, além de possuir flexibilidade para rápidas mudanças de topologia, e não apresentarem barreiras em relação aos padrões e equipamentos, o oposto por exemplo ao caso do sistema PLC (Power Line Communications). Devido à natureza difusora do canal sem fio, segurança nesse tipo de rede é um dos pontos mais críticos, já que um ataque de qualquer natureza pode provocar perturbações e blackouts na rede elétrica, ou gerar problemas de privacidade, na situação em que atacantes passivos (eavesdroppers) interceptam mensagens da rede com o intuito de obter algum tipo de benefício. Esta segunda situação, de ataques passivos, será abordada neste trabalho. Além das tradicionais técnicas de criptografia geralmente utilizadas para aumentar a segurança de redes de comunicação, outra área que vem recentemente despertando interesse da comunidade científica é a área de segurança na camada física, a qual é baseada em conceitos da teoria da informação de Shannon. Neste trabalho, utiliza-se as técnicas de codificação de rede para aumentar a segurança na camada física da parte de múltiplo acesso de uma rede de comunicação sem fio, em que dois transmissores possuem informações independentes para um destino em comum, na presença de um eavesdropper. Utilizando-se a probabilidade de outage com restrições de sigilo como métrica, mostra-se através de resultados analíticos e numéricos que o sigilo pode ser aumentado através da codificação de rede, quando comparada com a transmissão direta e com as técnicas de cooperação tradicionais. / Smart grids represent future of electrical power systems . These kind of networks must be robust to load fluctuations as well as have smart monitoring and intelligent management in real-time fashion . Based on the aforementioned needs, many authors propose the use of wireless communication systems in order to meet these demands, due to their efficient tradeoff between low-cost and high-seed when compared to wired connections such as optical fibens or metallic cables, and, in addition, they are flexible to topology changes and do not have constrainsts in terms of standards and devices, the opposite for example to the case of PLC(Power Line Comminications) .Due to the broadcast nature of the wireless medium , security is onde of the critical issues in smart grids since the occurrence of attacks can lead to load fluctuations and blackouts in the electrical system, or generate secrecy problems, in the situation where passive eaversdroppers intercept messages in the network aiming to obtain some kind of benefit . This second case of passive attacks will be addressed in the work. In addition to classical cryptography strategies commonly used to increase the security in communications systems another area which has been studied by the scientific community is the physical-layer security, which is based on the Shannon’s information theory. In this work, we use the network coding technique as tool to increase the physical-layer in a mulple access wireless network, where two users have independent information to transmit to a common destination, in the presence of an eavesdropper. By using the secrecy outage probability as the metric, we show through theoretic and numerical results that the network security can be increased through the use of network coding when compared to the transmission and traditional cooperative techniques.

Smart grids representam o futuro das redes elétricas. Estes tipos de redes devem ser robustas a flutuações de carga e devem possuir monitoramento e gerenciamento inteligente e em tempo real. Para que essas demandas sejam possíveis, é preciso uma comunicação de dados de alta velocidade, flexível e de baixo custo. Dentro dessas características, muitos autores propõem a utilização de sistemas de comunicação sem fio, os quais possuem um custo de implantação mais baixo que redes ópticas ou cabeadas, além de possuir flexibilidade para rápidas mudanças de topologia, e não apresentarem barreiras em relação aos padrões e equipamentos, o oposto por exemplo ao caso do sistema PLC (Power Line Communications). Devido à natureza difusora do canal sem fio, segurança nesse tipo de rede é um dos pontos mais críticos, já que um ataque de qualquer natureza pode provocar perturbações e blackouts na rede elétrica, ou gerar problemas de privacidade, na situação em que atacantes passivos (eavesdroppers) interceptam mensagens da rede com o intuito de obter algum tipo de benefício. Esta segunda situação, de ataques passivos, será abordada neste trabalho. Além das tradicionais técnicas de criptografia geralmente utilizadas para aumentar a segurança de redes de comunicação, outra área que vem recentemente despertando interesse da comunidade científica é a área de segurança na camada física, a qual é baseada em conceitos da teoria da informação de Shannon. Neste trabalho, utiliza-se as técnicas de codificação de rede para aumentar a segurança na camada física da parte de múltiplo acesso de uma rede de comunicação sem fio, em que dois transmissores possuem informações independentes para um destino em comum, na presença de um eavesdropper. Utilizando-se a probabilidade de outage com restrições de sigilo como métrica, mostra-se através de resultados analíticos e numéricos que o sigilo pode ser aumentado através da codificação de rede, quando comparada com a transmissão direta e com as técnicas de cooperação tradicionais. / Smart grids represent future of electrical power systems . These kind of networks must be robust to load fluctuations as well as have smart monitoring and intelligent management in real-time fashion . Based on the aforementioned needs, many authors propose the use of wireless communication systems in order to meet these demands, due to their efficient tradeoff between low-cost and high-seed when compared to wired connections such as optical fibens or metallic cables, and, in addition, they are flexible to topology changes and do not have constrainsts in terms of standards and devices, the opposite for example to the case of PLC(Power Line Comminications) .Due to the broadcast nature of the wireless medium , security is onde of the critical issues in smart grids since the occurrence of attacks can lead to load fluctuations and blackouts in the electrical system, or generate secrecy problems, in the situation where passive eaversdroppers intercept messages in the network aiming to obtain some kind of benefit . This second case of passive attacks will be addressed in the work. In addition to classical cryptography strategies commonly used to increase the security in communications systems another area which has been studied by the scientific community is the physical-layer security, which is based on the Shannon’s information theory. In this work, we use the network coding technique as tool to increase the physical-layer in a mulple access wireless network, where two users have independent information to transmit to a common destination, in the presence of an eavesdropper. By using the secrecy outage probability as the metric, we show through theoretic and numerical results that the network security can be increased through the use of network coding when compared to the transmission and traditional cooperative techniques.

In this thesis, we investigate physical-layer network coding in an L × M × K relay network, where L source nodes want to transmit messages to K sink nodes via M relay nodes. We focus on the information processing at the relay nodes and the compute-and-forward framework. Nested lattice codes are used, which have the property that every linear combination of codewords is a valid codeword. This property is essential for physical-layer network coding. Because the actual network coding occurs on the physical layer, the network coding coefficients are determined by the channel realizations. Finding the optimal network coding coefficients for given channel realizations is a non-trivial optimization problem. In this thesis, we provide an algorithm to find network coding coefficients that result in the highest data rate at a chosen relay. The solution of this optimization problem is only locally optimal, i.e., it is optimal for a particular relay. If we consider a multi-hop network, each potential receiver must get enough linear independent combinations to be able to decode the individual messages. If this is not the case, outage occurs, which results in data loss. In this thesis, we propose a new strategy for choosing the network coding coefficients locally at the relays without solving the optimization problem globally. We thereby reduce the solution space for the relays such that linear independence between their decoded linear combinations is guaranteed. Further, we discuss the influence of spatial correlation on the optimization problem. Having solved the optimization problem, we combine physical-layer network coding with physical-layer secrecy. This allows us to propose a coding scheme to exploit untrusted relays in multi-user relay networks. We show that physical-layer network coding, especially compute-and-forward, is a key technology for simultaneous and secure communication of several users over an untrusted relay. First, we derive the achievable secrecy rate for the two-way relay channel. Then, we enhance this scenario to a multi-way relay channel with multiple antennas. We describe our implementation of the compute-and-forward framework with software-defined radio and demonstrate the practical feasibility. We show that it is possible to use the framework in real-life scenarios and demonstrate a transmission from two users to a relay. We gain valuable insights into a real transmission using the compute-and-forward framework. We discuss possible improvements of the current implementation and point out further work. / In dieser Arbeit untersuchen wir Netzwerkcodierung auf der Übertragungsschicht in einem Relay-Netzwerk, in dem L Quellen-Knoten Nachrichten zu K Senken-Knoten über M Relay-Knoten senden wollen. Der Fokus dieser Arbeit liegt auf der Informationsverarbeitung an den Relay-Knoten und dem Compute-and-Forward Framework. Es werden Nested Lattice Codes eingesetzt, welche die Eigenschaft besitzen, dass jede Linearkombination zweier Codewörter wieder ein gültiges Codewort ergibt. Dies ist eine Eigenschaft, die für die Netzwerkcodierung von entscheidender Bedeutung ist. Da die eigentliche Netzwerkcodierung auf der Übertragungsschicht stattfindet, werden die Netzwerkcodierungskoeffizienten von den Kanalrealisierungen bestimmt. Das Finden der optimalen Koeffizienten für gegebene Kanalrealisierungen ist ein nicht-triviales Optimierungsproblem. Wir schlagen in dieser Arbeit einen Algorithmus vor, welcher Netzwerkcodierungskoeffizienten findet, die in der höchsten Übertragungsrate an einem gewählten Relay resultieren. Die Lösung dieses Optimierungsproblems ist zunächst nur lokal, d. h. für dieses Relay, optimal. An jedem potentiellen Empfänger müssen ausreichend unabhängige Linearkombinationen vorhanden sein, um die einzelnen Nachrichten decodieren zu können. Ist dies nicht der Fall, kommt es zu Datenverlusten. Um dieses Problem zu umgehen, ohne dabei das Optimierungsproblem global lösen zu müssen, schlagen wir eine neue Strategie vor, welche den Lösungsraum an einem Relay soweit einschränkt, dass lineare Unabhängigkeit zwischen den decodierten Linearkombinationen an den Relays garantiert ist. Außerdem diskutieren wir den Einfluss von räumlicher Korrelation auf das Optimierungsproblem. Wir kombinieren die Netzwerkcodierung mit dem Konzept von Sicherheit auf der Übertragungsschicht, um ein Übertragungsschema zu entwickeln, welches es ermöglicht, mit Hilfe nicht-vertrauenswürdiger Relays zu kommunizieren. Wir zeigen, dass Compute-and-Forward ein wesentlicher Baustein ist, um solch eine sichere und simultane Übertragung mehrerer Nutzer zu gewährleisten. Wir starten mit dem einfachen Fall eines Relay-Kanals mit zwei Nutzern und erweitern dieses Szenario auf einen Relay-Kanal mit mehreren Nutzern und mehreren Antennen. Die Arbeit wird abgerundet, indem wir eine Implementierung des Compute-and-Forward Frameworks mit Software-Defined Radio demonstrieren. Wir zeigen am Beispiel von zwei Nutzern und einem Relay, dass sich das Framework eignet, um in realen Szenarien eingesetzt zu werden. Wir diskutieren mögliche Verbesserungen und zeigen Richtungen für weitere Forschungsarbeit auf.

Abstract The thesis deals with the priváte banking in the Czech Republic and in Liechtenstein. The goal is to analyze concrete services that the client can expect in both of these countries. Large topic in this thesis is the lombard credit, which is quite a typical product in western countries but not that known among Czech investors. As well as the thesis describes all the mechanisms around it.

Within this thesis, we investigate the possibilities of physical layer secrecy for two special system models. In detail, we study beamforming and protection strategies in the Multiple-Input Single-Output (MISO) Gaussian Wiretap Channel (WTC) and the Gaussian two-hop relay WTC with multiple antennas at transmitter and receiver. In both system models, we examine the influence of partial Channel State Information (CSI) on the link to the eavesdropper and compare the achievable secrecy rates with the case of full CSI. We show for the MISO WTC that in the fast fading scenario the Beamforming Vector (BV) can be optimized such that the ergodic secrecy rate is maximized with regard to the degree of channel knowledge. Further we show that the ergodic secrecy rate can be significantly increased by usage of Artificial Noise (AN), if applied in a smart way. This means that the degree of channel knowledge on the link to the eavesdropper influences the portion of power that is spent for AN at the transmitter as well as the direction, in which the AN signal is sent. In addition, we apply the same beamforming and protection strategies to the slow fading scenario and find that these techniques also reduce the secrecy outage probability. For the two-hop relay WTC, we introduce Information Leakage Neutralization (IN) as a new protection strategy. If applied to a system model, where the transmitter has full CSI, the instantaneous secrecy rate performs almost as well as the instantaneous capacity of the peaceful system without an eavesdropper. The IN protected scheme outperforms the AN protected approach and performs much better than any beamforming scheme without additional protection mechanism. Another positive aspect of the IN protected scheme in the case of full CSI is that conventional channel codes can be applied instead of wiretap codes. For the case of partial CSI, where the transmitter has only an outdated estimate on the channel between relay and the eavesdropper, we show that the IN protected scheme can also be applied. Here, it strongly depends on the channel realizations and the delay of the estimate, whether the IN or the AN protection scheme should be applied. / In dieser Arbeit wird das Leistungsvermögen der Sicherheit auf der physikalischen Schicht anhand von zwei speziellen Systemmodellen untersucht. Im Detail werden Beamforming- und Absicherungsstrategien im gaußschen Multiple-Input Single-Output (MISO) Wiretap Channel (WTC) und dem gaußschen Two-hop Relay WTC mit mehreren Antennen am Sender und Empfänger studiert. In beiden Systemmodellen wird der Einfluss von partieller Kanalkenntnis zum Abhörer betrachtet und die so erreichbaren Sicherheitsraten mit denen verglichen, die bei voller Kanalkenntnis erreichbar sind. Für den MISO WTC kann gezeigt werden, dass für Kanäle mit schnellem Schwund der Beamforming-Vektor in Hinblick auf die ergodische Sicherheitsrate unter Berücksichtigung des Grades der Kanalkenntnis optimiert werden kann. Zudem kann durch die intelligente Verwendung von künstlichem Rauschen (Artificial Noise, AN) die ergodische Sicherheitsrate signifikant erhöht werden. Hierbei nimmt der Grad der Kanalkenntnis direkt Einfluss auf die Aufteilung der Leistung zwischen Daten- und AN-Signal am Sender sowie auch auf die Richtung, in der das AN-Signal gesendet wird. Zudem kann gezeigt werden, dass dieselben Beamforming- und Absicherungsstrategien ebenfalls die Sicherheitsausfallwahrscheinlichkeit für Kanäle mit langsamem Schwund minimieren. Im gaußschen Two-hop Relay WTC wird Information Leakage Neutralization (IN) als neuartige Absicherungsstrategie eingeführt. Diese Absicherungsstrategie erreicht nahezu dieselben instantanen Raten wie ein friedvolles System ohne Abhörer, wenn es bei voller Kanalkenntnis am Sender eingesetzt wird. Weiterhin sind durch die IN-Absicherungsstrategie höhere Raten erreichbar als durch den Einsatz von AN. Zusätzlich kann im Fall von voller Kanalkenntnis auf den Einsatz von Wiretap-Codes verzichtet werden. Auch im Fall partieller Kanalkenntnis, wo der Sender nur eine veraltete Schätzung des Kanals zwischen Relay und Abhörer besitzt, kann gezeigt werden, dass die IN-Absicherungsstrategie angewendet werden kann. Hierbei hängt es jedoch stark von den Kanalrealisierungen und dem Alter der Kanalschätzung ab, ob die IN- oder die AN-Absicherungsstrategie bessere Ergebnisse bringt und daher angewandt werden sollte.

In this thesis, we investigate physical-layer network coding in an L × M × K relay network, where L source nodes want to transmit messages to K sink nodes via M relay nodes. We focus on the information processing at the relay nodes and the compute-and-forward framework. Nested lattice codes are used, which have the property that every linear combination of codewords is a valid codeword. This property is essential for physical-layer network coding. Because the actual network coding occurs on the physical layer, the network coding coefficients are determined by the channel realizations. Finding the optimal network coding coefficients for given channel realizations is a non-trivial optimization problem. In this thesis, we provide an algorithm to find network coding coefficients that result in the highest data rate at a chosen relay. The solution of this optimization problem is only locally optimal, i.e., it is optimal for a particular relay. If we consider a multi-hop network, each potential receiver must get enough linear independent combinations to be able to decode the individual messages. If this is not the case, outage occurs, which results in data loss. In this thesis, we propose a new strategy for choosing the network coding coefficients locally at the relays without solving the optimization problem globally. We thereby reduce the solution space for the relays such that linear independence between their decoded linear combinations is guaranteed. Further, we discuss the influence of spatial correlation on the optimization problem. Having solved the optimization problem, we combine physical-layer network coding with physical-layer secrecy. This allows us to propose a coding scheme to exploit untrusted relays in multi-user relay networks. We show that physical-layer network coding, especially compute-and-forward, is a key technology for simultaneous and secure communication of several users over an untrusted relay. First, we derive the achievable secrecy rate for the two-way relay channel. Then, we enhance this scenario to a multi-way relay channel with multiple antennas. We describe our implementation of the compute-and-forward framework with software-defined radio and demonstrate the practical feasibility. We show that it is possible to use the framework in real-life scenarios and demonstrate a transmission from two users to a relay. We gain valuable insights into a real transmission using the compute-and-forward framework. We discuss possible improvements of the current implementation and point out further work. / In dieser Arbeit untersuchen wir Netzwerkcodierung auf der Übertragungsschicht in einem Relay-Netzwerk, in dem L Quellen-Knoten Nachrichten zu K Senken-Knoten über M Relay-Knoten senden wollen. Der Fokus dieser Arbeit liegt auf der Informationsverarbeitung an den Relay-Knoten und dem Compute-and-Forward Framework. Es werden Nested Lattice Codes eingesetzt, welche die Eigenschaft besitzen, dass jede Linearkombination zweier Codewörter wieder ein gültiges Codewort ergibt. Dies ist eine Eigenschaft, die für die Netzwerkcodierung von entscheidender Bedeutung ist. Da die eigentliche Netzwerkcodierung auf der Übertragungsschicht stattfindet, werden die Netzwerkcodierungskoeffizienten von den Kanalrealisierungen bestimmt. Das Finden der optimalen Koeffizienten für gegebene Kanalrealisierungen ist ein nicht-triviales Optimierungsproblem. Wir schlagen in dieser Arbeit einen Algorithmus vor, welcher Netzwerkcodierungskoeffizienten findet, die in der höchsten Übertragungsrate an einem gewählten Relay resultieren. Die Lösung dieses Optimierungsproblems ist zunächst nur lokal, d. h. für dieses Relay, optimal. An jedem potentiellen Empfänger müssen ausreichend unabhängige Linearkombinationen vorhanden sein, um die einzelnen Nachrichten decodieren zu können. Ist dies nicht der Fall, kommt es zu Datenverlusten. Um dieses Problem zu umgehen, ohne dabei das Optimierungsproblem global lösen zu müssen, schlagen wir eine neue Strategie vor, welche den Lösungsraum an einem Relay soweit einschränkt, dass lineare Unabhängigkeit zwischen den decodierten Linearkombinationen an den Relays garantiert ist. Außerdem diskutieren wir den Einfluss von räumlicher Korrelation auf das Optimierungsproblem. Wir kombinieren die Netzwerkcodierung mit dem Konzept von Sicherheit auf der Übertragungsschicht, um ein Übertragungsschema zu entwickeln, welches es ermöglicht, mit Hilfe nicht-vertrauenswürdiger Relays zu kommunizieren. Wir zeigen, dass Compute-and-Forward ein wesentlicher Baustein ist, um solch eine sichere und simultane Übertragung mehrerer Nutzer zu gewährleisten. Wir starten mit dem einfachen Fall eines Relay-Kanals mit zwei Nutzern und erweitern dieses Szenario auf einen Relay-Kanal mit mehreren Nutzern und mehreren Antennen. Die Arbeit wird abgerundet, indem wir eine Implementierung des Compute-and-Forward Frameworks mit Software-Defined Radio demonstrieren. Wir zeigen am Beispiel von zwei Nutzern und einem Relay, dass sich das Framework eignet, um in realen Szenarien eingesetzt zu werden. Wir diskutieren mögliche Verbesserungen und zeigen Richtungen für weitere Forschungsarbeit auf.

Aujourd’hui, le renforcement de la sécurité des systèmes de communications devient une nécessité, par anticipation du développement des ordinateurs quantiques et des nouvelles attaques qui en découleront. Cette thèse explore deux techniques complémentaires permettant d’assurer la confidentialité des données transmises sur des liens sans-fils. Dans la première partie de ce travail, nous nous intéressons au schéma de cryptographie à clé publique basée sur des réseaux de points, qui représente une des techniques les plus prometteuses pour la cryptographie post-quantique. En particulier, nous considérons le cryptosystème Goldreich-Goldwasser-Halevi (GGH), pour lequel nous proposons un nouveau schéma utilisant les GLD. Dans la seconde partie de ce travail, nous étudions la sécurité des canaux de diffusion multi-utilisateur, ayant accès à des mémoires de caches, en présence d'un espion. Nous considérons deux contraintes de sécurité: la contrainte de sécurité individuelle et la contrainte de sécurité jointe. Nous dérivons des bornes supérieure et inférieure pour le compromis sécurisé capacité-mémoire en considérant différentes distributions de cache. Afin d'obtenir la borne inférieure, nous proposons plusieurs schémas de codage combinant codage wiretap, codage basé sur la superposition et codage piggyback. Nous prouvons qu'il est plus avantageux d'allouer la mémoire de cache aux récepteurs les plus faibles. / Today, there is a real need to strengthen the communication security to anticipate the development of quantum computing and the eventual attacks arising from it. This work explores two complementary techniques that provide confidentiality to data transmitted over wireless networks. In the first part, we focus on lattice-based public-key cryptography, which is one of the most promising techniques for the post-quantum cryptography systems. In particular, we focus on the Goldreich-Goldwasser-Halevi (GGH) cryptosystem, for which we propose a new scheme using GLD lattices. In the second part of this work, we study the security of multi-user cache-aided wiretap broadcast channels (BCs) against an external eavesdropper under two secrecy constraints: individual secrecy constraint and joint secrecy constraint. We compute upper and lower bounds on secure capacity-memory tradeoff considering different cache distributions. To obtain the lower bound, we propose different coding schemes that combine wiretap coding, superposition coding and piggyback coding. We prove that allocation of the cache memory to the weaker receivers is the most beneficial cache distribution scenario.