Multi-channel information encryption technology has been implemented by metasurfaces owing to their superior capability in manipulating phase, amplitude, wavelength and polarization of incident light. However, any non-full-channel decoding may lead to the leakage of secret information. To further improve the security of information, in this paper, we propose a channel shared information encoding scheme by integrating visual secret sharing scheme with metasurface-based phase-encoding technique. The secret information can be reconstructed only by decoding all the wavelength channels of the metasurface, whiles meaningless images would be extracted in other channel decoding processes, without revealing any original information. The simulated results show the feasibility and adjustability of our encryption system, which can be potentially applied in future optical information security systems.
Multi-channel information encryption technology has been implemented by metasurfaces owing to their superior capability in manipulating phase, amplitude, wavelength and polarization of incident light. However, any non-full-channel decoding may lead to the leakage of secret information. To further improve the security of information, in this paper, we propose a channel shared information encoding scheme by integrating visual secret sharing scheme with metasurface-based phase-encoding technique. The secret information can be reconstructed only by decoding all the wavelength channels of the metasurface, whiles meaningless images would be extracted in other channel decoding processes, without revealing any original information. The simulated results show the feasibility and adjustability of our encryption system, which can be potentially applied in future optical information security systems.
Secret sharing is a promising technology for information encryption by splitting the secret information into different shares. However, the traditional scheme suffers from information leakage in decryption process since the amount of available information channels is limited. Herein, we propose and demonstrate an optical secret sharing framework based on the multi-dimensional multiplexing liquid crystal (LC) holograms. The LC holograms are used as spatially separated shares to carry secret images. The polarization of the incident light and the distance between different shares are served as secret keys, which can significantly improve the information security and capacity. Besides, the decryption condition is also restricted by the applied external voltage due to the variant diffraction efficiency, which further increases the information security. In implementation, an artificial neural network (ANN) model is developed to carefully design the phase distribution of each LC hologram. With the advantage of high security, high capacity and simple configuration, our optical secret sharing framework has great potentials in optical encryption and dynamic holographic display.
Abstract Metasurfaces that consist of a monolayer of photonic artificial atoms are emerging as attractive materials for optical wavefront-shaping and polarization-control devices. By integrating nanophotonics with a phase-encoding technique, we demonstrate theoretically an information authentication method using dielectric metasurfaces that can be verified without information disclosure at visible wavelengths. The required secured diffraction pattern can be simply achieved by a metasurface hologram with a small number of pixels, which means increased efficiency and lower costs of production. Although the decrypted image is noisy, it can be authenticated by recognition algorithms where the primary image is used as a reference. The results show that the dielectric metasurface approach, providing great flexibility in the design of the wavefront of light and compatible with the CMOS technology, can be potentially applied in optical information security.
Quantum secret sharing (QSS) is a multi-party quantum communication protocol that can be realized with bipartite entanglement and relative phase encoding. Previous implementations typically encoded the phase in the pump, applying it across the entire source bandwidth, thereby limiting scalability via wavelength multiplexing. In contrast, we present a variant of the standard QSS protocol that leverages frequency correlations to connect multiple users with a single source. The secret owner, who has access to the source, encodes classical information by applying frequency-dependent phase modulation to a broadband polarization-entangled photon pair. Each frequency channel, therefore, provides an independent QSS session among the secret owner and a pair of users. We demonstrate state fidelities of at least 90% for a channel pair of the 200 GHz ITU grid, a configuration that can be extended to more than 40 frequency bins for the same grid spacing. Notably, despite the use of large grid spacing and the experimental limitations, the system achieves full connectivity of a network of 7 users while maintaining a key fraction of 0.4 bits/photon. These results provide a resource-efficient path toward multi-user secret sharing over wavelength-multiplexed networks, eliminating the need for multiple two-photon or multi-photon sources.
In today’s ever-evolving information security landscape, the demand for robust encryption techniques is on the rise. Superior to traditional encryption schemes, one-time pad encryption provides unparalleled security due to its reliance on a unique, nonreusable key for each message. Here, a novel one-time pad incoherent encryption paradigm based on optical metasurface ciphertext and dynamic visual keys has been developed. The proposed encryption scheme exploits the inherent security of the one-time pad by ensuring information confidentiality through the use of a random and nonreusable key. Based on this foundation, optical metasurfaces are initially used to encode the ciphertext and visual key, introducing an additional layer of complexity and security. In addition, the system incorporates dynamic visual keys using a spatial light modulator, adding dynamic and visually intuitive dimensions to the encryption process. These dynamic keys enhance the security of the communication channel by introducing variability into the encryption parameters, making it extremely difficult for unauthorized parties to predict or analyze cryptographic patterns. The result is a highly secure and robust incoherent encryption system that can be found to have potential applications in secure communication and data protection domains.
Towards growing challenges of information security and authentication, various optical techniques based on holography, diffraction, interference, metasurfaces, etc., deliver promising solutions with low energy consumption and parallel high-speed information processing. Here, we report on a new dimension–second-order coherence found in the well-known Hanbury Brown and Twiss (HBT) effect–for performing optical authentication and secret sharing. We develop a method to generate a pair of correlated phase-only masks, each of which is distributed to a shareholder and can produce a specific pattern as authentication under coherent illumination, while two secret images are encrypted in the mutual information of two masks. By combining two masks in two configurations, two secret images can be extracted through spatially cascaded display under coherent illumination and intensity correlation under incoherent illumination, respectively. Conspicuously, two extremes of coherence–spatially coherent or incoherent–will enable the encoding and decoding of two different images with the same phase masks, indicating that the first-order and second-order coherence can be two independent channels for optical cryptography just like other degrees of freedom of light (e.g., polarization). Moreover, we demonstrate a polarization-multiplexing scheme to achieve polarization-selective HBT-type optically secret-sharing with increased capacity, and this type of polarization-phase masks can be readily replaced with metasurfaces.
As a typical technology for optical encryption, phase retrieval algorithms have been widely used in optical information encryption and authentication systems. This paper presents three applications of two-dimensional (2D) phase retrieval for optical encryption and authentication: first, a hierarchical image encryption system, by which multiple images can be hidden into cascaded multiple phase masks; second, a multilevel image authentication system, which combines (t, n) threshold secret sharing (both t and n are positive integers, and t ≤ n ) and phase retrieval, and provides both high-level and low-level authentication; and finally, a hierarchical multilevel authentication system that combines the secret sharing scheme based on basic vector operations and the phase retrieval, by which more certification images can be encoded into multiple cascaded phase masks of different hierarchical levels. These three phase retrieval algorithms can effectively illustrate phase-retrieval-based optical information security. The principles and features of each phase-retrieval-based optical security method are analyzed and discussed. It is hoped that this review will illustrate the current development of phase retrieval algorithms for optical information security and will also shed light on the future development of phase retrieval algorithms for optical information security.