Security of Digital Images using Dynamical Systems

Abstract

Cryptography as an art and science concerns mainly the protection of communicating data e.g., digital image, audio and video files, from unauthorized interceptions as well as fraudulent changes. It builds under the assumption that if the behavior is obvious, the point of attack is achievable, so that the aim here is to conceal any noticeable information about the original data. These security needs are established by means of a well-designed cryptosystem, in which the evaluation of its quality is quantified by, to which extent it can be employed in practice for data encryption and decryption transformations without the key being broken. For decades of years, serious efforts have been devoted to investigate and develop means from various branches of knowledge, and then employed them as tools in the area of designing secure cryptosystems. Of particular interest, are those proposals involve the use of dynamical systems. The very appealing observed point is that, the attractive features of dynamical systems e.g., unpredictability, complex chaotic behavior can be reached by simple mathematical models. This latter has been the leading point to establish the bridge between the theory of dynamical systems and cryptography. From the viewpoint of, exploiting and developing these complex models as a base in the design of efficient cryptographic means.

This thesis involves the use of two different types of dynamical systems in discrete-time, namely cellular automata-based dynamical systems and chaos-based dynamical systems, and investigates the existing cryptographic methods related to them, to provide new and efficient proposals for image content preservation. The key contributions throughout this thesisare: firstly,anovelfastandefficientrandomizedencryptioncipherbasedonquadtree decomposition mechanism (QTD) in combination with special class of cellular automata, namelyonedimensional4thorderreversiblememorycellularautomata(RMCA)tailoredto digital image encryption; secondly, a new image encryption method based on chaos jointly special class of cellular automata, namely two dimensional 4th order reversible memory cellular automata (RMCA) with Moore neighborhood; thirdly, a new chaotic cipher algorithm for efficient and secure image content preservation, specialized for both standard and medical images. Each of these proposals is evaluated by means of the common and typical assessment tools. The obtained results are interesting in terms of security degrees and time-consuming, and point to the advocacy of the designed cipher algorithms.