The purpose of this work was first to describe the requirements for cryptographic protocols. Furthermore, the classification of these protocols should have been made with specific examples given. The aim of the next part of the work was to describe the methods which are suitable for description and modeling of cryptographic protocols. This work also addressed the analysis of cryptographic protocols by appropriate analytical means. The CSP method for modeling of the cryptographic protocols was applied in the practical part. The Yahalom protocol was selected as a protocol suitable for modeling. Two analysis was made. The first analysis concerned the standard version of the Yahalom protocol, which was tested to the requirements of cryptographic properties of the secrecy and authenticity. The second analysis was based on the possibility of disclosure of the key, including counterexamples and traces given by FDR. The first analysis did not reveal any weakening, in terms of two cryptographic properties. To demonstrate the possibility of FDR, Yahalom protocol was modified in order to cause the situation when the disclosure of keys appears. FDR then finds the exact procedure that an intruder must make to get the possession of the key.

The reader will be familiar with selected concepts of cryptography consited in this work. AES algorithm was selected in conjunction with the description of architecture and software for programming graphic cards (CUDA, OpenCL), in order to create its GPU-accelerated version. This thesis tries to map APIs for communication with crypto-coprocessors, which exist in kernels of Linux/BSD operating systems (CryptoAPI, OCF). It examines this support in the cross-platform OpenSSL library. Subsequently, the work discusses the implementation details, achieved results and integration with OpenSSL library. The conclusion suggests how the developed application could be used and briefly suggests its usage directly by the operating system kernel.

This work deals with design and implementation of the system for document management and versioning. The first part contains description of related work. In the second part, information security concepts and security model, upon which application is build, is discussed. Third part contains description of designed system and its typical use in a form of sequence diagram. Fourth part introduces cryptographic protocol used in this work. Next follows the description of implementation and security analysis of developed system. The output of this work is cryptographic protocol for document management and versioning, and client-server application implementing this protocol.

Despite being a relatively young field, cryptography taught us how to perform seemingly-impossible tasks, which now became part of our everyday life. One of them is secure multiparty computation (MPC), which allows mutually distrustful parties to jointly perform a computation on their private inputs, so that each party only learns its prescribed output, but nothing else. In this work we deal with two longstanding challenges of MPC: adaptive security and deniability (or, incoercibility). A protocol is said to be adaptively secure, if it still guarantees security for the remaining honest parties, even if some parties turn dishonest during the execution of the protocol, or even after the execution. (In contrast, statically secure protocols give security guarantees only when the set of dishonest parties is fixed before the execution starts.) While adaptive security threat model is often more realistic than the static one, there is a huge gap between efficiency of statically and adaptively secure protocols: adaptively secure protocols often require more complicated constructions, stronger assumptions, and more rounds of interaction. We improve in efficiency over the state of the art in adaptive security for a number of settings, including the first adaptively secure MPC protocol in constant number of rounds, under assumptions comparable to those of static protocols (previously known protocols required as many rounds of interaction as the depth of the circuit being computed). The second challenge we deal with is providing resilience in the situation where an external coercer demands that participants disclose their private inputs and all their secret keys - e.g. via threats, bribe, or court order. Deniable (or, incoercible) protocols allow coerced participants to convincingly lie about their inputs and secret keys, thereby still maintaining their privacy. While the concept was proposed more than twenty years ago, to date secure protocols withstanding coercion of all participants were not known, even for the simple case of encryption. We present the first construction of such an encryption scheme, and then show how to combine it with adaptively secure protocols to obtain the first incoercible MPC which withstands coercion of all parties.

Quantum communication protocols invoke one of the most fundamentallaws of quantum mechanics, namely the superposition principle whichleads to the no-cloning theorem. During the last three decades, quantumcryptography have gone from prospective theories to practical implementationsscalable for real communication. Scientist from all over the world havecontributed to this major progress, starting from Stephen Wiesner, CharlesH. Bennett and Gilles Brassard who all developed the theory of QuantumKey Distribution (QKD). QKD lets two users share a key through a quantumchannel (free space or fiber link) under unconditionally secure circumstances.They can use this key to encode a message which they thereaftershare through a public channel (internet, telephone,...). Research developmentshave gone from the ordinary 2-User Quantum Key Distribution oververy small free space distances to distances over 200 km in optical fiber andQuantum Key Distribution Networks.As great experimental achievements have been made regarding QKDprotocols, a new quantum communication protocol have been developed,namely Quantum Secret Sharing. Quantum Secret Sharing is an extensionof an old cryptography scheme called Secret Sharing. The aim of secretsharing is to split a secret amongst a set of users in such a way that thesecret is only revealed if every user of this set is ready to collaborate andshare their part of the secret with other users.We have developed a 5-User QKD Network through birefringent singlemode fiber in two configurations. One being a Tree configuration and theother being a Star configuration. In both cases, the number of users, thedistances between them and the stability of our setup are all well competitivewith the current worldwide research involving similar work.We have also developed a Single Qubit Quantum Secret Sharing schemewith phase encoding through single mode fiber with 3, 4 and 5 parties. Thelatter is, to the best of our knowledge, the first time a 5-Party Single QubitQuantum Secret Sharing experiment has been realized.

Cette thèse porte sur les problèmes algorithmiques qui apparaissent lorsque l'on souhaite mettre en œuvre un cryptosystème basé sur un code correcteur d'erreur ou bien une cryptanalyse d'un tel système. L'intérêt de ces système provient de leur excellente complexité algorithmique, meilleure de plusieurs ordres de grandeurs en termes de complexité que les schémas à clé publique traditionnels. Ils fournissent également une alternative crédible aux systèmes actuels qui pour la plupart se repose sur la théorie des nombres et sur le problème de la factorisation et celui du logarithme discret. Outre l'absence de preuve mathématique de la réelle difficulté de ces problèmes, P. Shor a montré que ces deux problèmes pouvaient être résolus en temps polynomial dans le modèle de l’ordinateur quantique. Cet ordinateur quantique est encore loin d'être fonctionnel mais il faudra, le jour venu, disposer d'alternatives de confiance et disposant de mises en œuvre performantes. / This thesis is about algorithmic problems arising when someone wants to implement a cryptosystem based on error correcting codes or a cryptanalysis of such a system. The benefits of these systems come from their excellent algorithmic complexity, better of several orders than the classical public key schemes. They also bring a credible alternative to the current systems that for most of them rely on number theory and on the problems of factorisation and discrete logarithm. P.Shor showed that these two problems could be solved in polynomial time in the quantum computer model. This computer is far from being operational but we will need alternatives we can trust and that have efficient implementations.

Cryptographic accumulators are a tool for compact set representation and secure set membership proofs. When an element is added to a set by means of an accumulator, a membership witness is generated. This witness can later be used to prove the membership of the element. Typically, the membership witness has to be synchronized with the accumulator value, and to be updated every time another element is added to the accumulator. In this work we propose an accumulator that, unlike any prior scheme, does not require strict synchronization. In our construction a membership witness needs to be updated only a logarithmic number of times in the number of subsequent element additions. Thus, an out-of-date witness can be easily made current. Vice versa, a verifier with an out-of-date accumulator value can still verify a current membership witness. These properties make our accumulator construction uniquely suited for use in distributed applications, such as blockchain-based public key infrastructures.

Indiana University-Purdue University Indianapolis (IUPUI) / The Internet of Things (IoT) is a natural evolution of the Internet and is becoming more and more ubiquitous in our everyday home, enterprise, healthcare, education, and many other aspects. The data gathered and processed by IoT networks might be sensitive and that calls for feasible and adequate security measures. The work in this thesis describes the use of the Wi-Fi technology in the IoT connectivity, then proposes a new approach, the Proactive Wireless Protected Access (PWPA), to protect the access networks. Then a new end to end (e2e) IoT security model is suggested to include the PWPA scheme. To evaluate the solutions security and performance, rstly, the cybersecurity triad: con dentiality, integrity, and availability aspects were discussed, secondly, the solutions performance was compared to a counterpart e2e security solution, the Secure Socket Layer security. A small e2e IoT network was set up to simulate a real environment that uses HTTP protocol. Packets were then collected and analyzed. Data analysis showed a bandwidth e ciency increase by 2% (Internet links) and 12% (access network), and by 344% (Internet links) and 373% (access network) when using persistent and non-persistent HTTP respectively. On the other hand, the analysis showed a reduction in the average request-response delay of 25% and 53% when using persistent and non-persistent HTTP respectively. This scheme is possibly a simple and feasible solution that improves the IoT network security performance by reducing the redundancy in the TCP/IP layers security implementation.

No description available.

The operation of the Solitaire algorithm is based on a deck of cards, including two different jokers. We use the computer to simulate the Solitaire algorithm and analyze the key stream which is generated by the algorithm.We mainly analyze the maximum cycle length of the key stream and doNIST test.