Abstract

Many image encryption algorithms have been proposed over recent years Refs. 1-8, to cite a few. Many of these algorithms can be implemented using optical techniques taking advantage of both the natural two dimensional (2D) imaging capabilities of optics and the parallelisms achievable with optical processing. Optical systems are also capable of encrypting real world 3D objects [9]. The output of an encryption system is complex valued. Digital holographic techniques have been used to record high quality approximations of both the amplitude and phase of complex valued wavefronts output by the optical encryption systems [9,10]. Digital compression techniques have been used to enable efficient storage and transmission of encrypted holographic data over digital communication channels [11,12]. Though many optical encryption techniques have been proposed in the recent years, a systematic analysis of the strengths and weaknesses of these algorithms has not been undertaken yet, to the best of our knowledge. Optical encryption algorithms with all their advantages mentioned above, are yet to undergo rigorous cryptanalysis which many conventional cryptographic algorithms are subjected to. There are instances in the literature when an encryption mechanism is shown to be robust to blind decryption for a limited number of keys in the key space. But this is not sufficient to evaluate the strength of an encryption algorithm. This work attempts to systematically study the strengths of some of the well known image encryption algorithms.