Abstract
The attractors in many fractional-order chaotic systems have more complex dynamics than their integer-order systems. Consequently, there is a recent trend of exploring fractional chaotic systems for the design of image cryptosystems. The fractional derivative orders can act as part of secret key. Recently, an image encryption algorithm is suggested based on synchronized fractional-order chaotic systems. In this paper, a security appraisal is actioned to evince that the encryption algorithm is completely breakable under chosen-plaintext attack, has no mandatory plaintext sensitivity, and unsafe. Moreover, an enhanced version of encryption scheme is accounted to improve its attack defensibleness, plaintext sensitivity and inherent encryption strength. Experimental analyses are exercised and statistical results are catered to manifest the improved performance. The anticipated enhanced version has high security, consistency and practicability for encryption of digital images. (C) 2015 The Authors. Published by Elsevier B.V.