The speckle correlation technique is applied to ciphertext-only attack (COA) on optical cryptosystem based on double random phase encoding. According to the inherent merits of speckle correlation, we have revealed a fact that the ciphertext’s autocorrelation is essentially identical to the plaintext’s own autocorrelation. Then, a plaintext image can be directly reconstructed from the autocorrelation of its corresponding ciphertext by employing a iterate phase-retrieval algorithm. This could then lead to a potential security flaw because an unauthorized user could directly retrieve the plaintext from an intercepted ciphertext by performing proposed COA approach. Meanwhile, a series of numerical simulations will also be provided to verify the validity and feasibility of our proposed COA method.
We propose a novel method to achieve the purpose of hierarchical authentication based on two beams interference. In this method, different target images indicating different authentication levels are analytically encoded into corresponding phase-only masks (phase keys) and amplitude-only masks (amplitude keys) with the help of a random phase mask, which is created in advance and acts as the fixed lock of this authentication system. For the authentication process, a legal user can obtain a specified target image at the output plane if his/her phase key, and amplitude key, which should be settled close against the fixed internal phase lock, are respectively illuminated by two coherent beams. By comparing the target image with all the standard certification images in the database, the system can thus verify the user’s identity. In simple terms, this system can not only confirm the legality of a user but also distinguish his/her identity level. Moreover, in despite of the internal phase lock of this system being fixed, the crosstalk between different pairs of keys hold by different users is low. Theoretical analysis and numerical simulation are both provided to demonstrate the validity of this method.
We present an optical image encryption method based on a modified radial shearing interferometer. In our encryption
process, a plaintext image is first encoded into a phase-only mask (POM), and then modulated by a random phase mask
(RPM), the result is regarded as the input of the radial shearing interferometer and divided into two coherent lights, one
of which will be further modulated by a random amplitude mask (RAM). After all, these two coherent lights will
interfere with each other leading to an interferogram, i.e., ciphertext. And the ciphertext can be used to retrieve the
plaintext image with the help of a recursive algorithm and all correct keys. The aforementioned encryption procedure can
be achieved digitally or optically while the decryption process can be analytically accomplished. Numerical simulation is
provided to demonstrate the validity of this method.