Securing multiple color information by optical coherent superposition based spiral phase encoding

•A multiple image encryption using superposition and spiral phase mask is proposed.•The selected SPM is introduced as an encrypted image for multiple color images.•The decoding procedure is free from cross talk and noise effects in real time.•The only need is to send the parameters to multiple-user, but not the key itself.•Numerical simulations show the viability of the proposed method.

A new optical multiple-color image cryptosystem using optical coherent superposition based spiral phase encoding is proposed, which can be applied to achieve a nonlinear multiple-image encryption of the same size. This multiplexed coding scheme is lensless, non time-consuming and decoding procedure is free from cross talk and noise effects in real time. In this contribution, a color image is decomposed into three independent channels, i.e., red, green and blue. Each channel is then divided into an arbitrarily selected spiral phase mask (SPM) and a spiral key mask (SKM). The selected SPM is introduced as an encrypted image for multiple color images. The SKMs are employed as different decryption keys for different images. That means, only need is to send the construction parameters (as the order, the wavelength, the focal length, and the radius) of the SPM independently to multiple-user, but not the key itself, so it enhances robustness against existing attacks than double random phase encoding techniques. Moreover, the maximum data can be securely handled with a single parameter variation. The encryption process can be performed digitally while the decryption process is very simple and can be implemented using optoelectronic architecture. A set of numerical simulation results confirm the feasibility and effectiveness of the proposed cryptosystem for multiple-color image encryption.