الفهرس 
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Abstract
Securing images using optical techniques has drawn increasing attention due to its inherent features like high-speed and multidimensional processing capabilities. Recently, optical multiple-image encryption (MIE) has attracted increasing attention, since several images can be simultaneously encrypted to enhance the cryptosystem capacity and efficiency. However, conventional MIE techniques are based on multiplexing approaches that naturally yield annoying crosstalk which diminishes the quality of decoded images and limits the encryption capacity. We present an asymmetric cryptosystem for multiple color images which is silhouette-free and crosstalk-free based on unequal modulus decomposition (UMD) in the gyrator transform (GT) domains. It is demonstrated that this method eliminates the crosstalk problems which are well-known in previous multiple-image cryptosystems. The cryptosystem is verified robust against occlusion, noise, statistical attacks, and the chosen-plaintext attack. The quality of the output images is found unaffected by the number of encrypted images which offers ultimately high multiplexing capacity. Typical image encryption generally aims to protect a plain secret image by transforming it into a visually noise-like cipher image that gives no information about the original secret image. However, the noisy appearance indicates the presence of encrypted information and thus results in a several attacks. We propose a visually meaningful image cryptosystem which offers three levels of security: image-appearance security, image-analysis security, and image-content security. Compact and efficient polarization-assisted electro-optical implementations of the proposed cryptosystems have been proposed. The immunity of the cryptosystem against the statistical and classical attacks including the chosen-plaintext attack and the chosen-ciphertext attack has been demonstrated.