Improving the Security of Image Encryption by using Two Chaotic Maps

Abstract

ABSTRACT During the recent years several chaotic image encryption algorithms based on one dimensional (1- D ) have been proposed, but the drawbacks of small key space, low speed, and low security in 1- D chaotic cryptosystems are obvious. This paper proposes a new image encryption technique based on 1- D and 2- D chaotic maps which provide more security and big key space. The 1- D chaotic system is induced from a mathematical combination between the logistic map and the cubic chaotic map. It has the advantage of bigger key space and high security analysis such as key space analysis, statistical analysis and sensitivity analysis were carried out. The proposed system uses 1- D and 2- D chaotic maps for simultaneous encryption of the components R, G, B of the colored image; these three components affect each other. So, the security and confidentiality of image data become more important. The security of digital images and performance speed has become more important since the communications of digital information over network occur more frequently. An image encryption has applications in various fields for example; the internet communication, the multimedia systems, the medical imaging, Tele-medicine and the military communication. The image encryption's aim is to convert the original image to another image that is hard to understand. However, image encryption differs from text encryption due to some intrinsic features of images which include bulk data capacities, high redundancy, strong correlations among pixels, etc. These features make conventional cipher systems such as DES, AES and RSA unsuitable for practical image encryption [1]. The chaos theory is used in cryptography due to its intrinsic features. These properties of chaos includes: sensitivity to initial condition and control parameters, random like behavior and mixing property, etc [2]. Several chaos based image encryption approaches have been described. The first is the confusion approach where the position of pixels scrambled without changing the values of pixels, the application of this approach does not guarantee a good level of security [3]. The second approach is the diffusion which aims to change the value of each pixel in the whole image [4]. Other approach shuffles the positions of plain-image in spatial domain by cat map [5-7]. To enhance the security, the majority of methods propose to mix between more than one approach simultaneously. Some conditions should be fulfilled such as a large key space, randomness of the cipher-image and a high sensitivity on the initial conditions. In [8], an image encryption scheme based on improved 3-