Security-enhanced optical encryption based on JTC architecture with confused ciphertext

Optical Correlators for Cryptosystems and Image Recognition: A Review

“…Among the optical encryption solutions, the most common is the DRPE (double random phase encoding), developed in 1995 by Réfrégier and Javidi. The setup involves a 4-f classical processor or a JTC, that performs both the encryption and decryption [ 29 ].…”

“…DRPE presents, however, several drawbacks: a complex ciphertext is difficult to record; the precision of the alignment must be very high; the fabrication of the phase conjugation mask is challenging; in the decryption process, one needs the precise complex conjugate of one of the RPMs employed as a key [ 29 , 31 ]. Moreover, DRPE cryptosystems are prone to attacks such as KPA (known-plaintext attack), CPA (chosen-plaintext attack) and COA (ciphertext-only attack) [ 32 ].…”

“…To overcome the drawbacks of the classical encryption techniques mentioned in the previous subsection, the joint transform correlator (JTC) was proposed as an alternative solution. Thus, the architecture of a cryptosystem based on JTC has become the preferred choice in most applications [ 29 ], due to advantages such as the possibility of using without an extremely precise alignment of the optical components (because the object and the key are both in the same plane); the elimination of the requirement of a complex-conjugate of the encryption key for decryption; the identity between the JPS (joint power spectrum) and the ciphertext [ 25 , 28 , 33 ].…”

“…Then, in the focal plane of the same FTL, the multiplication between the key mask and ciphertext is performed. Afterwards, a second FTL is placed, and in its focal plane the recovery of the plaintext is finally obtained [ 29 ]. Thus, the encrypted image consists in a distribution of the intensity in the Fourier plane, whereas the decrypted image results after using the same key as for the encrypted part [ 31 ].…”

“…The latter drawback is due to the linearity of the encryption setup in the conventional scheme (the initial image and the ciphertext are linearly related). Although various proposals decreased their vulnerability to attacks, by eliminating the linearity, most of these solutions also increase both the complexity and the price of the system, which is a disadvantage in practical applications [ 29 ]. Other proposals lead to a simplification of the encryption part, mainly the optical setup, and respectively to an improvement of the decrypted image quality [ 31 ].…”