Improved decryption quality and security of a joint transform correlator-based encryption system

Abstract

Abstract. Some image encryption systems based on modified double random phase encoding and joint transform correlator architecture produce low quality decrypted images and are vulnerable to a variety of attacks. In this work, we analyse the algorithm of some reported methods that optically implement the double random phase encryption in a joint transform correlator. We show that it is possible to significantly improve the quality of the decrypted image by introducing a simple nonlinear operation in the encrypted function that contains the joint power spectrum. This nonlinearity also makes the system more resistant to chosen-plaintext attacks. We additionally explore the system resistance against this type of attacks when a variety of probability density functions are used to generate the two random phase masks of the encryption-decryption process. Numerical results are presented and discussed.

Nonlinear optical security system based on a joint transform correlator in the Fresnel domain

“…This processor typically requires strict optical alignment, which in practice is difficult to attain. To alleviate this constraint, the optical DRPE can be also performed by means of a joint transform correlator (JTC) architecture that also shows other advantages [13][14][15][16][17][18]. With the JTC, a CCD camera captures the intensity distribution of the joint power spectrum (JPS) as the encrypted data in the Fourier domain, while the classical DRPE method requires the recording of complex-valued information.…”

“…An alternative solution is given in [18], where the key code is represented by real-valued data. Another solution that involves the nonlinear processing of the JPS is given in [16].…”

“…The possibility of applying nonlinear transformations onto the JPS has been explored in order to improve both the security of the encrypted image and the image quality in the retrieval of the decrypted image [16] and in image verification [30].…”

Photon-counting multifactor optical encryption and authentication

“…From these pieces of information the attacker may recover crucial information of the security system such as the hidden decryption key. For the interested reader, the security flaws of the DRPE are analysed elsewhere ( [15][16][17] for a 4 f -processor, [39][40][13][14] for the JTC architecture).…”

“…Most of the optical security systems usually deal with a single primary image (for instance, an object, a plaintext, a signature, a biometric signal) as authenticator [2][3][4][5][6][7][10][11][12][13][14][18][19][20][21][22][23]. Some approaches permit to store multiple primary images, either in an optical memory [9] or in a single encrypted distribution [24][25][26][27], with the purpose of sequential and independent one-by-one decryption.…”