Abstract We propose a comprehensive and efficient optical-cryptographic encryption scheme to improve the security of vulnerable optical encryption systems. Based on cryptography theory, we increase data protection using diffusion-confusion processes acting in the input and output of the optical encryption scheme. The new enhanced ciphertext has attributes of a one-way function that is easy to achieve but almost impossible to revert without the correct random phase masks used for diffusion-confusion operations. Despite the straightforward design, combining optical, cryptographic, and chaos methods increases the number of encryption–decryption keys raising two significant concerns. First, the management and transmission of several keys carry a high storage footprint, and second, it impairs the optical high-speed information processing capability. We overcome these two drawbacks by applying a new optical keystream synthesizer based on the stochastic speckle nature and a maximum entropy constraint in a forward–backward propagation algorithm. This new approach quickly replicates the necessary keystream in the encryption–decryption stations offering higher security and efficiency than other reported systems. We validate the feasibility of this proposal by synthesizing an experimental keystream and performing 24-bit data encryption–decryption. Then, we verify the security improvement of two vulnerable cryptosystems and their robustness against cryptanalysis attacks. Finally, we perform experimental encryption–decryption.
Abstract We propose a comprehensive and efficient optical-cryptographic encryption scheme to improve the security of vulnerable optical encryption systems. Based on cryptography theory, we increase data protection using diffusion-confusion processes acting in the input and output of the optical encryption scheme. The new enhanced ciphertext has attributes of a one-way function that is easy to achieve but almost impossible to revert without the correct random phase masks used for diffusion-confusion operations. Despite the straightforward design, combining optical, cryptographic, and chaos methods increases the number of encryption–decryption keys raising two significant concerns. First, the management and transmission of several keys carry a high storage footprint, and second, it impairs the optical high-speed information processing capability. We overcome these two drawbacks by applying a new optical keystream synthesizer based on the stochastic speckle nature and a maximum entropy constraint in a forward–backward propagation algorithm. This new approach quickly replicates the necessary keystream in the encryption–decryption stations offering higher security and efficiency than other reported systems. We validate the feasibility of this proposal by synthesizing an experimental keystream and performing 24-bit data encryption–decryption. Then, we verify the security improvement of two vulnerable cryptosystems and their robustness against cryptanalysis attacks. Finally, we perform experimental encryption–decryption.
The rapid growth in the storage and transmission of visual data across communication, sensing, and decision-making systems requires image encryption methods that are both computationally efficient and resilient against quantum-enabled adversaries. Classical chaotic encryption offers desirable properties such as sensitivity, unpredictability, and large key spaces, but its practical use is limited by restricted chaotic ranges, and conventional confusion–diffusion mechanisms often fail to eliminate structural redundancies in images. This thesis furthers the field by developing novel chaotic and gate-efficient quantum image encryption architectures. First, it introduces a new cosine-modulated polynomial chaotic map and validates its dynamical and statistical suitability for cryptographic key generation. Second, it designs lightweight yet effective chaotic primitives, including the Single-Round Single S-Box (SRSS) confusion mechanism and the featureaware diffusion scheme (PermutEx) that address the limitations in breaking correlation and maintaining efficiency. Third, these components are integrated into a complete endto- end chaos-based encryption framework that combines feature-driven segmentation, adaptive permutation, and dynamic confusion, demonstrating strong security across entropy, correlation, and differential metrics. Finally, the thesis advances two quantum image encryption architectures, i.e., a chaos-enhanced quantum image encryption framework that strengthens quantum confusion and diffusion mechanisms, and a gate-efficient architecture that reduces circuit depth and multi-qubit operations while retaining robust security. The proposed architectures achieve improved computational efficiency compared to existing chaos-based and quantum image encryption techniques, by reducing redundant operations, minimising circuit depth, and enabling lightweight yet effective confusion-diffusion processes. Consequently, this thesis provides a way forward for advancing image encryption by integrating chaotic and quantum approaches, offering practical steps for protecting visual data in the post-quantum era.
Optical encryption inherently provides strong security advantages, with hybrid optoelectronic systems offering additional degrees of freedom by integrating optical and algorithmic domains. However, existing optical encryption schemes heavily rely on electronic computation, limiting overall efficiency, while the physical keys are susceptible to damage, compromising both security and system stability. To overcome these challenges, we introduce the Quasi Periodic Optical Key (QPOK), which combines long range order with short range disorder, enabling enhanced security and robustness against damage within a single platform. By leveraging diffraction symmetry, our design enables optics-driven encryption, effectively shifting the optoelectronic balance toward photonic processing. Moreover, we innovatively apply deep learning to reconstruct the complex optical ciphertext field using only amplitude data and cryptographic keys, simultaneously achieving data compression and improved security. Within this framework, the key space includes continuously tunable parameters such as wavelength, propagation distance, phase modulation, and Q-POK geometry, significantly expanding cryptographic diversity. Our system also demonstrates robust cryptographic reliability by reducing inter-class distances by over 50% and tolerating up to 20% ciphertext loss. Our framework represents a new generation of physically grounded, algorithmically enhanced optical cryptosystems, laying a foundational pathway for scalable, hardware-integrated information security paradigms.
Optical encryption inherently provides strong security advantages, with hybrid optoelectronic systems offering additional degrees of freedom by integrating optical and algorithmic domains. However, existing optical encryption schemes heavily rely on electronic computation, limiting overall efficiency, and the physical keys are susceptible to damage, compromising both security and system stability. To overcome these challenges, we introduce the quasi-periodic optical key (Q-POK), which combines long-range order with short-range disorder, enabling enhanced security and robustness against damage within a single platform. By leveraging diffraction symmetry, our design enables optics-driven encryption, effectively shifting the optoelectronic balance toward photonic processing. Moreover, we innovatively apply deep learning to reconstruct the complex optical ciphertext field using only amplitude data and cryptographic keys, simultaneously achieving data compression and improved security. Within this framework, the key space includes continuously tunable parameters such as wavelength, propagation distance, phase modulation, and Q-POK geometry, significantly expanding cryptographic diversity. Our system also demonstrates robust cryptographic reliability by reducing inter-class distances by over 50% and tolerating up to 20% ciphertext loss. Our framework represents a generation of physically grounded, algorithmically enhanced optical cryptosystems—laying a foundational pathway for scalable, hardware-integrated information security paradigms.
In conventional interference-based optical encryption schemes, a potential cracker can retrieve partial information (silhouette) of the secret image using only one phase-only mask (POM). We resolve this drawback using a phase-blend operation and piecewise linear chaotic map (PWLCM) to further encode the POMs. One cannot recover a secret image visibly when inverse phase-blend operation and inverse chaotic permutation are not carried out with the correct decryption keys. Chaotic parameters of PWLCM, and random phase-angle function in the phase-blend operation enlarge the key space and improve the security of the proposed system greatly. Numerical simulations and optoelectronic experiments are performed to verify the effectiveness of the proposed scheme.
We report a novel optical encryption strategy that utilizes highly scattered wavefront of light field to encrypt the plaintext and exploits a scattering medium as the unique physical key. For information decryption, an imaging technique based on the speckle-correlation scattering matrix is adopted to directly extract the wavefront information from speckles, i.e., the ciphertext. The decryption relies on the transmission matrix of the scattering medium which serves as the unique key. In particular, different parts of a scattering medium have absolutely different TMs. Thus, even if attackers get the cryptosystem and repeat the measurement process, they cannot recover the key without knowing the exact part of the medium we used. The security of this scheme is further guaranteed by the advantage that data cannot be leaked without a large percentage (>60%) of the key eavesdropped. In addition, its feasibility and advantage are demonstrated experimentally.
Optical techniques for information security have drawn a lot of attention in recent years. The development of cryptanalysis strategies will also have a positive promotion for the cryptosystems themselves. However, most of the present publications on cryptanalysis of optical cryptosystems are focusing only on theoretical analysis but not on experimental verification. In this paper, a practical optical cryptanalysis method using wavefront shaping is proposed. Considering that the confusion and diffusion of information in the optical cryptosystem are actually caused by scattering effect of random phase mask(s), the proposed method employs a point source function and the feedback-based optimization algorithm, which can obtain an equivalent key of the optical cryptosystem. In such a way, the confusion and diffusion of the random phase mask(s) in the cryptosystem could be removed successfully. To the best of our knowledge, this is the first time the attack strategy from the perspective of wavefront shaping can be seen, and one of the biggest advantages is that it could get an equivalent key of the cryptosystem without deducing its original keys.