A Novel Algorithm for Block Encryption of Digital Image Based on Chaos

This paper proposes a novel image block encryption algorithm based on three-dimensional Chen chaotic dynamical system. The algorithm works on 32-bit image blocks with a 192-bit secret key. The idea is that the key is employed to drive the Chen’s system to generate a chaotic sequence that is inputted to a specially designed function G, in which we use new 8x8 S-boxes generated by chaotic maps (Tang, 2005). In order to improve the robustness against differential cryptanalysis and produce desirable avalanche effect, the function G is iteratively performed several times and its last outputs serve as the keystreams to encrypt the original image block. The design of the encryption algorithm is described along with security analyses. The results from key space analysis, differential attack analysis, and information entropy analysis, correlation analysis of two adjacent pixels prove that the proposed algorithm can resist cryptanalytic, statistical and brute force attacks, and achieve a higher level of security. The algorithm can be employed to realize the security cryptosystems over the Internet. DOI: 10.4018/jcini.2011010104 60 International Journal of Cognitive Informatics and Natural Intelligence, 5(1), 59-74, January-March 2011 Copyright © 2011, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. established: (1) Ergodicity in chaos vs. confusion in cryptography; (2) Sensitive dependence on initial conditions and control parameters of chaotic maps vs. diffusion property of a good cryptosystem for a slight change in the plaintext and in the secret key; (3) Random-like behavior of deterministic chaotic-dynamics which can be used for generating pseudorandom sequences as key sequences in cryptography. In recent years, the transmission of digital images over the Internet or personal digital mobile phones has been highly developed. Secure storage and transmission of digital images are becoming critically important. Most traditional ciphers, such as DES, IDEA, and AES are not suitable to conduct the digital image encryption in real time due to large data volume involved. Hence, the main purpose of this paper is to design a new image block encryption algorithm by using non-traditional methods such as chaos theory. A brief review is in order on existing results of chaos-based encryption scheme. Yen et al. (2000) proposed a chaotic key-based algorithm (CKBA) in which a binary sequence as a key is generated based on a chaotic map. According to the binary sequence, image pixels are rearranged and then XORed with the key. However, as pointed out later in (Li, 2002), this algorithm has some drawbacks: it is vulnerable to the chosen or known-plain-text attack using only one plain image, and its security to brute-force attack is also questionable. Chen et al. (2004) used a 3D Arnolad’s cat map for the purpose of substitution and employed Chen’s chaotic system for generating key streaming and diffusion. A more complex system which combines discreteand continuous-time chaotic systems has been proposed by Guan et al. (2005). Recently, Tong et al. (2009) presented a new compound two-dimensional chaotic functions design which acted as a chaotic sequence generator, and suggested a feedback image encryption scheme by using the new compound chaos and perturbation technology based on 3D Baker map. At the same time, in (Lian, 2009) the author employed a chaotic neural network (CNN) composed of a chaotic neuron layer and a linear neuron layer to construct a block cipher, in which the chaotic neuron layer realizes data diffusion and the linear neuron layer realizes data confusion, and the two layers are repeated for several times to strengthen the cipher. Obviously, these research results laid a good foundation to the subsequent studies on the chaos-based image encryption algorithm. Motivated by the aforementioned results, a new image block encryption algorithm based on three-dimensional Chen dynamical system is proposed in this paper. Since cryptosystems play a pivotal role in a very important engineering application of cognitive informatics, i.e., information assurance and security, the subject topic of this paper is within the broad scope of cognitive informatics. The main novelty of the algorithm can be summarized as follows: (1) the 3D Chen system with complex dynamical behaviors is adapted; (2) within the algorithm, a 192bit secret key is used to drive the Chen system and the keystreams are generated through iteratively performing a specially designed function G; (3) when designing the function G, we use new 8 8 ́ S-boxes produced by chaotic maps in (Tang, 2005) in order to obtain desirable confusion and diffusion properties. Results of various types of analysis show that the new algorithm is highly secure for practical image encryption applications. The remaining part of the paper is organized as follows. We first introduce the Chen chaotic system and show its chaotic attractors. The design of the encryption algorithm is then described in details, along with some experiments. Following that are the analyses that address the security performance of the proposed algorithm. Finally, conclusions and future work are drawn. 14 more pages are available in the full version of this document, which may be purchased using the "Add to Cart" button on the product's webpage: www.igi-global.com/article/novel-algorithm-block-encryptiondigital/53147?camid=4v1 This title is available in InfoSci-Journals, InfoSci-Journal Disciplines Computer Science, Security, and Information Technology. Recommend this product to your librarian: www.igi-global.com/e-resources/libraryrecommendation/?id=2