Double image encryption based on phase–amplitude mixed encoding and multistage phase encoding in gyrator transform domains

We present a novel method for double image encryption that is based on amplitude–phase mixed encoding and multistage random phase encoding in gyrator transform (GT) domains. In the amplitude–phase mixed encoding operation, a random binary distribution matrix is defined to mixed encode two primitive images to a single complex-valued image, which is then encrypted into a stationary white noise distribution by the multistage phase encoding with GTs. Compared with the earlier methods that uses fully phase encoding, the proposed method reduces the difference between two primitive images in key space and sensitivity to the GT orders. The primitive images can be recovered exactly by applying correct keys with initial conditions of chaotic system, the GT orders and the pixel scrambling operation. Numerical simulations demonstrate that the proposed scheme has considerably high security level and certain robustness against data loss and noise disturbance.

► We present a double image encryption scheme based on phase–amplitude mixed encoding.
► Iterative gyrator transform (GT) is applied to strengthen the encryption security.
► The method reduces the difference between two primitive images in key space.
► The sensitivity of decryption results to GT orders is greatly enhanced.
► Simulation results verify the validity and feasibility of the proposed method.