Optical encryption and authentication scheme based on phase-shifting interferometry in a joint transform correlator

In this paper, the effectiveness of the cryptosystem based on phase-shifting technique (PST) in a joint transform correlator (JTC) is evaluated. It is shown that the cryptosystem has some inherent drawbacks, for example, since the plaintexts are required to obtain the phase-shifting intensity patterns in the first phase extraction step, which means that the information of the plaintexts should be known by the authorized users before decryption processing. It seems impossible and paradoxical in the practical case. Moreover, the cryptosystem can only achieve binary plaintexts encryption while the inputs of this scheme cannot be the gray-scale or color images. To address these issues, we propose an encryption and authentication scheme based on PST in a JTC. By introducing a preprocessing operation including an intensity modulator based on histogram equalization and photon-counting (PC) operator, a photon-limited binary distribution of the plaintexts is obtained and used as the input of the cryptosystem. Due to this design, our proposed scheme can achieve encryption for different kinds of images such as binary, gray-scale and color images using same optical setup without any changes, which can simplify the optical implementation. Furthermore, a post-processing operator to extract phase information of encoded images and authenticate the decoded images is introduced. Since no useful information will be released from the photon-limited binary decoded images obtained using correct decryption keys and the interface of the database storing the plaintexts is only given to the authorized users, an additional security layer is established. This is the first time to report the use of binary intensity pattern in a scheme based on PSI in a JTC for secured verification of different images.