Selective Hybrid Chaotic-Based Cipher for Real-Time Image Application

Abstract

Image encryption is much different from that of the texts due to the bulk data capacity and the high redundancy of images. Thus, traditional methods are difficult to be used for image encryption as their pseudo-random sequences have a small space. Chaotic cryptography uses the chaos theory in specific systems working such as computing algorithms to accomplish dissimilar cryptographic tasks in a cryptosystem with a fast throughput. For higher security, encryption is the approach to guard information and decrease its leakage. In this thesis, we showed some of the recent work on chaos-based cryptography, especially those cryptosystems with the Skew Tent Map (STM), which we address and evaluate in this thesis, as a large number of chaos-based cryptosystems, were implemented using it. We proposed a hybrid encryption scheme that combines both stream and block ciphering algorithms to achieve the required level of security with the minimum encryption time; this scheme is based on a mathematical model improved to cover the defects in a previous discredited model proposed by Masuda. The proposed chaos-based cryptosystem uses the improved STM (RQ-FSTM) as a substitution based on a lookup table to overcome various problems, such as the fixed point, the key space restrictions, and the limitation of mapping between plain text and cipher text. It uses the same map as a generator to change the byte posi- 9 tion to achieve the required confusion and diffusion effects. The proposed cryptosystem is flexible, efficient, and more robust against cryptanalysis. The robustness of the proposed cryptosystem was proven by the performance and the security analysis, as well as the high encryption speed (throughput). Depending on the results of the security analysis done on our cryptosystem, and after comparing the results with the previous cryptosystems. Our proposed system has a better dynamic key space than the previous ones using skew tent map with a difference that is more than the triple size, a double encryption quality that is much closer to the optimal quality and a better security analysis than the others in the literature with a speed convenient to the real-time applications.