Currently, chaotic cryptography is mainly concentrated on image encryption. Once-popular stream-encryption algorithms, e.g., textual data, are now rarely considered. This article studies how chaotic image-encryption algorithms can be used to encrypt text. The proposed approach to this problem consists of two stages: in the first stage, the text message is intended for encryption into an image; in the second step, the selected image-encryption algorithm is used. An example illustrates the efficiency of this method. In addition, the article presents measures used in image-encryption analysis that confirm the security of the obtained cipher-image, such as entropy (value close to 8), correlation of adjacent pixels (values close to 0), or measures related to differential cryptanalysis. The proposed method offers a new look at text encryption using chaos, by applying image-encryption algorithms already known from the literature.

One of the applications of dynamical systems with chaotic behavior is data encryption. Chaos-based cryptography uses chaotic dynamical systems as the basis for creating algorithms. The present article discusses a new dynamical system called M-map with its analysis: fixed points, bifurcation diagram, Lyapunov exponent, and invariant density. The obtained bifurcation diagram and the plot of the Lyapunov exponent (with a minimum value of $ln2$ and a maximum value of $ln4$) suggest that the so-called robust chaos characterizes this map. Moreover, the obtained results are compared with other dynamical systems used in cryptography. Additionally, the article proposes a new image encryption algorithm. It uses, among others, cyclically shifted S-box or saving encrypted pixels on the first or last free space in the cipher-image. The conducted analysis shows that the cipher-images are characterized by an entropy value close to 8, a correlation of adjacent pixels value close to 0, or values of Number of Pixel of Change Rate ($NPCR$) and Unified Average Changing Intensity ($UACI$) measures close to 100% and 33%, respectively.

This work presents a chaotic image encryption algorithm that acts on the binary level of the image for effective permutation, and on the byte level for substitution. The permutation step combines actions of bit level rearranging, and bit shuffling. Circular shift operations are used for bit shuffling, to reduce the execution time. Circular shifts are also applied to shuffle the permutation and substitution rules, effectively increasing security at a very low execution cost. The encryption keys are plaintext dependent, and a key mixing step in included, so that each part of the key affects all the subsequent encryption operations. For the encryption, a new Soboleva hyperbolic tangent based map is first designed. The dynamical behavior of the map is studied and shows robust chaos, and an absence of equilibria, meaning that it can generate hidden attractors. This map is used as an entropy source, along with a chaotic pseudo random number generator. The encryption process shows a good performance under a collection of tests, and has also a low execution time, 0.0134 sec for a 256x256 image, 0.0530 sec for a 512x512 image, and 0.2050 sec for a 1024x1024 image.

In this paper the combination of logistic and tent map is discussed. Some basic properties of the new dynamical system like Lyapunov exponent and density of the iterated variable are analyzed. Furthermore, applications of the discussed model in chaos based cryptography are presented.

This work provides a thorough review on the research topic of chaotification for discrete-time systems. Chaotification refers to the process of designing new chaotic maps, using existing maps from the literature as seed functions, with the goal of achieving a more complex behavior. This problem is of great theoretical interest, but also of practical importance, as highly complex chaotic systems are sought after in many applications. This review aims at providing a roadmap on the topic of chaotification, by presenting the recent developments in the topic, organized by the methodologies that are considered. Future challenges are also identified.