A dynamic block image encryption using variable-length secret key and modified Henon map

• Published in: Optik (Stuttgart) 2021-03, Vol.230, p.166307, Article 166307
• Main Authors: Zhao, Hongxiang, Xie, Shucui, Zhang, Jianzhong, Wu, Tong
• Format: Article
• Language: English
• Subjects: Block image encryption; Modified Henon map; Multidirectional dynamic block diffusion; SHA; Substitution without repetition; Variable-length key
• ISSN: 0030-4026; 1618-1336
• DOI: 10.1016/j.ijleo.2021.166307

In this paper, a dynamic block image encryption using variable-length key and modified Henon map is proposed. To surmount the defects of narrow chaotic range and frail chaotic behaviors when classical Henon map is implemented in practical situations, we design a simple modified Henon map with wide parameter range and high complexity. The Secure Hash Algorithm (SHA) is employed to obtain a 384-bit hash result of plain image considered as a raw key. A variable-length secret key (at least 128 bits), which is dynamically selective from the raw key, is regarded as a valid key to generate initial points of chaotic map. In confusion, we construct a chaotic but non-repetitive integer sequence to implement a substitution without repetition for disorganizing the high spatial relevance among pixels. This can sufficiently avert the problem of fixed points after a confusion, i.e., for any pixel within the confused image, its position will never overlap with the old one. In diffusion, we apply a multidirectional dynamic block diffusion mechanism to modify pixel values, which may not only spread the influences to whole image but reduce encryption time. The proposed scheme has been tested via various cryptographic analysis, and the security analysis demonstrates it has superior security and good efficiency.