Browsing by Author "Bourekouche, Hadjer"

Now showing 1 - 3 of 3

Contribution to chaotic encryption methods for digital data
(Université M'Hamed Bougara Boumerdès : Faculté de Technologie, 2024) Bourekouche, Hadjer; Belkacem, Samia(Directeur de thèse)
In this thesis, we investigate the development process of chaos-based image encryption algorithms from various perspectives, including the serious challenge of generating secure random number sequences for use as dynamic encryption keys. First, at the aim of improving the randomness and non-periodicity qualities of the basic pseudo-random number generators (PRNG) used as key-stream generators, we exploit the unique attributes of the logistic map (LM), logistic-sine system(LSS), linear feedback shift registers (LFSR), and nonlinear feedback shift register (NLFSR) to design new key-stream generators (namely: LSS-LFSR-PRNG, LM-NLFSR-PRNG, and LSS-NLFSR-PRNG). Therefore, our generators succeed in generating unlimited, random, and nonlinear sequences by passing the totality of the National Institute of Standard and Technology (NIST) statistical tests, and displayed strong cryptographic security, resulting in high entropy, high key sensitivity, and large key space exceeding 2^100. The second goal highlights the importance of selecting an appropriate chaos-based architecture for confusion and diffusion. The dimensions of the chaos-based confusion-diffusion architecture vary depending on the specific chaotic map being used. Hence, we design three confusion-diffusion algorithms of various levels (1D LM-based cryptosystem, 1D LM-Chebyshev-based cryptosystem, and 3D intertwining logistic map-cosine (ILM) based cryptosystem), to discuss and demonstrate the impact of choosing the appropriate dimension of the chaotic map on the vulnerability of a cryptosystem. It has been proven that higher-dimensional chaotic maps, such as 3D-ILM, can enhance the ability to resist exhaustive and statistical attacks by achieving desirable values of the number of pixels change rate (NPCR) and unified average changing intensity (UACI), while these maps are unable to maintain encryption speed. The third goal of this thesis is to improve the core of the mathematical model of chaos-based cryptosystems by boosting the chaotic complexity and chaotic range of basic one-dimensional chaotic maps. Where, we propose a new nonlinear chaotification system capable of producing 1D enhanced discrete chaotic maps (enhanced tangent-Logistic map T-LM, enhanced tangent-Sine map T-SM, and enhanced tangent-Chebyshev system T-CH), by applying tangent nonlinear transforms to the outputs of the existing chaotic maps. This strategy improves the performance of basic 1D chaotic maps by exhibiting better dynamical behavior, Lyapunov exponent, bifurcation, and larger chaotic intervals
Efficient image encryption scheme using a nonlinear shift register and chaos
(TARU PUBLICATIONS, 2024) Bourekouche, Hadjer; Belkacem, Samia; Messaoudi, Noureddine
Powerful cryptographic systems require a qualified random number generator. This research purposes to provide a comprehensive comparative analysis done on several of the well-known pseudo-random number generators (PRNGs) regarding their efficiency and resilience against crypto-analytical threats. These generators consist of the basic 8-bit Non- Linear Feedback Shift Register (NLFSR), the logistic map (LM), and our proposed hybrid random number generator named NLFSR-LM, which combines through XOR operation the sequences of the NLFSR with the LM to achieve a high quality of randomness. The performance of the created generator is examined and subsequently compared according to statistical tests of randomness alongside cryptographic features in terms of key space, key sensitivity and resistance to numerous attacks. The proposed generator produced good results and exhibited several interesting properties, such as a high degree of security, a sufficiently large key space, and it provided better randomness than other frequently used PRNGs.
Randomness evaluation of coupled chaotic maps via NIST tests: A comparative study
(IEEE, 2020) Bourekouche, Hadjer; Belkacem, Samia; Messaoudi, Noureddine
A vital requirement for any random number generator based on chaos is to ensure that the generated sequence always benefits of a significant level of randomness. It is critical to examine such sequences by means of Lyapunov exponents, bifur-cation diagrams, or other tests in order to accurately select the parameters of the dynamic system. However, the sequence’s randomness quality varies depending on the generator's design and must be examined in different ways. Therefore, we argue to use the National Institute of Standards and Technology (NIST) suite tests to evaluate and compare the randomness properties of two coupled systems found in existing literature: the logistic-sine system (LSS) and the logistic-tent system (LTS). The results reveal that the LSS has much superior statistical features in terms of randomness than the LTS in the range [3.1–4]. This conclusion will substantially affect the selection of the perfect chaotic map to create sequences of keys that match the requirements of cryptography applications.