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In this paper, a security enhancement for double random phase encoding (DRPE) by introducing a rear-mounted phase masking procedure is presented. Based on exhaustively studying the cryptanalysis achievements of DRPE and its variants, invalidation of the second lens, which plays a critical role in cryptanalyzing processes, is concluded. The improved system can exploit the security potential of the second lens and consequently strengthen the security of DRPE. Experimental results and security analyses are presented in detail to demonstrate the security potential of the proposed cryptosystem.

In recent years, the operation efficiency of chaos-based image cryptosystems has drawn much more concerns. However, the workload arised from floating point arithmetic in chaotic map iteration prevents the efficiency promotion of these cryptosystems. In this paper, we present a novel image encryption scheme using Gray code based permutation approach. The new permutation strategy takes full advantage of (n, p, k)-Gray-code achievements, and is performed with high efficiency. A plain pixel-related image diffusion scheme is introduced to compose a complete cryptosystem. Simulations and extensive security analyses have been carried out and the results demonstrate the high security and operation efficiency of the proposed scheme.

Recently, a double-image encryption scheme using local pixel scrambling technique and gyrator transform has been proposed [Opt Lasers Eng 2013; 51: 1327–31]. Through our simulations, there is serious cross-talk disturbance in the phase-based image when the encrypted data undergoes noise perturbation or occlusion attack. The disturbance will cause serious deterioration in the retrieved phase-based image and bring about visibility ambiguities to the receiver, and hence downgrades the practicability of the cryptosystem. In this paper, detailed analysis of the cross-talk disturbance in the original scheme will be firstly given out, and then the corresponding improvement is subsequently proposed. Numerical simulations results indicate that the improved scheme well address the cross-talk disturbance and further enhance the security of the original cryptosystem.