Digital image chaotic encryption and transmission using UIO

In present work, secure communication scheme for digital images based on discrete time unknown input observer (UIO) design blended with discrete time chaotic encryption is presented. Chaotic signals are pseudo random signals with no periodicity over infinite length. However, the series can be generated with the precise knowledge of the few parameters like system parameters and initial conditions of the chaotic system. With the given nature of pseudo-randomness and extreme sensitivity to parameters, chaotic sequences are ideal for encryption. In literature, these chaotic sequences are generally generated using continuous time chaotic systems. Since image data to be transmitted is in digital form and encryption algorithms are also executed on digital devices, so it is proposed to use discrete time chaotic communication scheme. Further, its effectiveness for encryption of digital images is also analyzed. To further enhance the security encrypted data is embedded in the dynamics of discrete time chaotic transmitter system. To recover the message at the receiver, design of discrete time UIO along with a procedure to recover unknown message signal using estimated states is given. Existence conditions for the UIO are analytically derived in terms of LMIs. Solution of these LMIs gives the observer design matrices. Robustness of UIO based chaotic communication scheme against attacks is analyzed by studying return maps of the transmitted signal. It is reported that security of chaotic communication scheme can be compromised by studying the return maps of the transmitted signal. To validate the proposed approach results of simulation and security analysis are presented.