Image encryption using radial Hilbert transform filter bank as an additional key in the modified double random fractional Fourier encoding architecture

We propose a method for image encryption using a radial Hilbert transform (RHT) filter bank in the factional Fourier transform (FRT) domain. The filter bank comprises of multiple integral order RHT filters. The scheme is implemented using the well-known double random phase encoding technique. The random phase functions, fractional orders of the FRT, and integral orders of the multiple RHT filters forming the filter bank are used as key parameters for encryption and decryption. Simulation results have been presented to analyze the performance of the proposed scheme with respect to variation in key parameters, and the schematic for its optical implementation has been presented. Effectiveness of the scheme is also shown against the noise, occlusion and attacks using partially correct random phase keys. The effect on decryption, of rotation of the RHT filter bank as well as some of the RHT filters of the filter bank has been studied. Simulation results are also presented to exhibit the performance of the technique against reshuffling the positions of the RHT filters during the decryption. Investigations have also been carried out to analyze the proposed technique against the chosen- and the known-plain-text attacks.