Security Analysis of Random Phase Encoding Based Image Encryption in Gyrator Transform Domains

Gyrator transform is a new tool for image encryption. In this paper, the security of image encryption based on random phase encoding in gyrator transform domains was analyzed. For image encryption with single random phase encoding and gyrator transform, the operation of random phase encoding only changes the phase angle of the original secret image instead of the amplitude of the image. So, the encryption security depends on the rotation angle used in gyrator transform. Based on the periodicity of gyrator transform, it is shown that, by equally dividing the period interval [0, 2 pi] of gyrator transform with enough great number and applying exhausted search, the rotation angle used in gyrator transform can be obtained approximately with known-plaintext attack. Then, the secret image can be decrypted with various qualities upon the precision of dividing the interval [0, 2 pi]. This result can be used as research foundation for further security analysis of image encryption in gyrator transform domains.