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We propose a method for fully phase image encryption based on double random-structured phase mask encoding in the gyrator transform (GT) domain. The security of the system is strengthened by parameters used in the construction of a structured phase mask (SPM) based on a devil's vortex Fresnel lens (DVFL). The input image is recovered using the correct parameters of the SPMs, transform orders of the GT, and conjugate of the random phase masks. The use of a DVFL-based SPM enhances security by increasing the key space for encryption, and also overcomes the problem of axis alignment associated with an optical setup. The proposed scheme can also be implemented optically. The computed values of mean squared error between the retrieved and the original image show the efficacy of the proposed scheme. We have also investigated the scheme's sensitivity to the encryption parameters, and robustness against occlusion and multiplicative Gaussian noise attacks.

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We have carried out a study of optical image encryption in the Fresnel transform (FrT) domain, using a random phase mask (RPM) in the input plane and a phase mask based on devil’s vortex toroidal lens (DVTL) in the frequency plane. The original images are recovered from their corresponding encrypted images by using the correct parameters of theFrTand the parameters of DVTL. The use of a DVTL-based structured mask enhances security by increasing the key space for encryption and also aids in overcoming the problem of axis alignment associated with an optical setup. The proposed encryption scheme is a lensless optical system and its digital implementation has been performed using MATLAB 7.6.0 (R2008a). The scheme has been validated for a grayscale and a binary image. The efficacy of the proposed scheme is verified by computing mean-squared-error (MSE) between the recovered and the original images. We have also investigated the scheme’s sensitivity to the encryption parameters and examined its robustness against occlusion and noise attacks.

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