Tabu Cryptanalysis of VMPC Stream Cipher

In the era of global informatization, transmitting and storing information in digital form it is very important to ensure an adequate level of security of ciphers used. Cryptanalysis deals with studying the level of security, thus exposing the weakness of theoretical and implemented cryptographic solutions. In this paper cryptanalysis of stream cipher VMPC using Tabu Search is shown. From estimates made on a full version of VMPC cipher we concluded that about 2157 possibilities needs to be checked in order to find the proper one, which would be the best attack known so far

Breaking Data Encryption Standard with a Reduced Number of Rounds Using Metaheuristics Differential Cryptanalysis

This article presents the author’s own metaheuristic cryptanalytic attack based on the use of differential cryptanalysis (DC) methods and memetic algorithms (MA) that improve the local search process through simulated annealing (SA). The suggested attack will be verified on a set of ciphertexts generated with the well-known DES (data encryption standard) reduced to six rounds. The aim of the attack is to guess the last encryption subkey, for each of the two characteristics Ω. Knowing the last subkey, it is possible to recreate the complete encryption key and thus decrypt the cryptogram. The suggested approach makes it possible to automatically reject solutions (keys) that represent the worst fitness function, owing to which we are able to significantly reduce the attack search space. The memetic algorithm (MASA) created in such a way will be compared with other metaheuristic techniques suggested in literature, in particular, with the genetic algorithm (NGA) and the classical differential cryptanalysis attack, in terms of consumption of memory and time needed to guess the key. The article also investigated the entropy of MASA and NGA attacks

Algorytmy metaheurystyczne w kryptoanalizie szyfrów strumieniowych

Metaheuristic algorithms are general algorithms allowing to solve various types of computational problems, usually optimization ones. In the dissertation, new versions of selected metaheuristic algorithms were developed: Tabu Search and Ant Colony Optimization algorithms. They have been adapted to solve the problem of cryptanalysis of stream ciphers, which are an important element of data protection processed and stored in information systems. Attempts to hide information from unauthorized persons have a long history. As early as the 5th century BC there was a simple Atbash substitution cipher among the Hebrew scholars. Although a lot has changed since then, and the art of encrypting information has undergone a significant transformation, the issue of confidentiality of communication is still important. Encryption is used wherever protection of transmitted or stored data, especially in information systems, is of key importance. Encryption is used when talking on the phone or logging in via the Internet to a bank account. It is also of great importance in the military. Encryption is an issue with a long history, still important and topical. The proposed Tabu Search and Ant Colony Optimization algorithms adapted to cryptanalysis were tested using three stream ciphers: RC4, VMPC and RC4+. This enabled the development of an attack independent of the design of the cipher itself, assuming that the internal state of the cipher can be represented as a permutation of numbers from a given range. For all proposed metaheuristic algorithms, four types of fitness functions have been tested, three of which are original ones. The original fitness functions enabled achieving better results for all three analysed metaheuristic algorithms compared to a function known from the literature. Each of the proposed algorithms were tested in terms of the impact of parameters values on the results they achieved. Also the results achieved by all three metaheuristic algorithms were compared to one another. The results obtained during cryptanalysis of smaller and full versions of the analysed ciphers with the use of Tabu Search were compared with the results obtained by other metaheuristic algorithms, showing that Tabu Search leads to better results than other metaheuristics. The results obtained using the Tabu Search algorithm were also compared to attacks known from the literature on selected stream ciphers. The results of the experiments indicate that for the VMPC and RC4+ ciphers, the proposed cryptanalysis algorithm using Tabu Search may be better than the cryptanalysis algorithms known so far. The results achieved by other metaheuristic algorithms considered were not as good as for Tabu Search, although it cannot be ruled out that further enhancement of these algorithms could improve the results

Analyse et Conception d'Algorithmes de Chiffrement Légers

The work presented in this thesis has been completed as part of the FUI Paclido project, whose aim is to provide new security protocols and algorithms for the Internet of Things, and more specifically wireless sensor networks. As a result, this thesis investigates so-called lightweight authenticated encryption algorithms, which are designed to fit into the limited resources of constrained environments. The first main contribution focuses on the design of a lightweight cipher called Lilliput-AE, which is based on the extended generalized Feistel network (EGFN) structure and was submitted to the Lightweight Cryptography (LWC) standardization project initiated by NIST (National Institute of Standards and Technology). Another part of the work concerns theoretical attacks against existing solutions, including some candidates of the nist lwc standardization process. Therefore, some specific analyses of the Skinny and Spook algorithms are presented, along with a more general study of boomerang attacks against ciphers following a Feistel construction.Les travaux présentés dans cette thèse s’inscrivent dans le cadre du projet FUI Paclido, qui a pour but de définir de nouveaux protocoles et algorithmes de sécurité pour l’Internet des Objets, et plus particulièrement les réseaux de capteurs sans fil. Cette thèse s’intéresse donc aux algorithmes de chiffrements authentifiés dits à bas coût ou également, légers, pouvant être implémentés sur des systèmes très limités en ressources. Une première partie des contributions porte sur la conception de l’algorithme léger Lilliput-AE, basé sur un schéma de Feistel généralisé étendu (EGFN) et soumis au projet de standardisation international Lightweight Cryptography (LWC) organisé par le NIST (National Institute of Standards and Technology). Une autre partie des travaux se concentre sur des attaques théoriques menées contre des solutions déjà existantes, notamment un certain nombre de candidats à la compétition LWC du NIST. Elle présente donc des analyses spécifiques des algorithmes Skinny et Spook ainsi qu’une étude plus générale des attaques de type boomerang contre les schémas de Feistel