Asymmetric multi-image encryption technology based on position multiplexing and computer-generated holography

The multi-image encryption method has the advantage of large information encryption capacity, which is conducive to the development of high-throughput cryptosystems. This paper proposes an asymmetric multi-image encryption and decryption technique based on position multiplexing and computer-generated holography (CGH). In the proposed encryption scheme, each channel adopts the phase-truncated asymmetric encryption method using double random phase encoding in the Fresnel domain with position multiplexing to encrypt a plaintext image. Then the complex amplitude distributions from each channel are superposed together and phase-truncated, which is further encrypted by off-axis CGH to obtain the final ciphertext. Additionally, to solve the problem of crosstalk noise in the decryption of multiple images, a new decryption framework is proposed. A constrained complex total variation (TV) regularizer, which explores the well-known sparsity in the gradient domain, and the implicit image prior from advanced denoisers, are introduced to enhance the well posedness of the nonconvex problem under limited measurements, and two-step iterative shrinkage-thresholding (TwIST) algorithm is used to accelerate the iterations. The system can flexibly encrypt and decrypt multi-frame images, e.g., in the case of encrypting four complex grayscale images, the decrypted plaintext images achieved an average correlation coefficient (CC) of 0.9938 and an average peak signal-to-noise ratio (PSNR) of 31.10 dB. The results demonstrate that the proposed encryption scheme not only efficiently achieves the encryption of multi-frame complex grayscale images, but also offers certain advantages concerning high encryption capacity, a large key space, flexible system parameter settings, and robust resistance against attacks.