The hologram, which is formed by phases coupled through cascade devices for secret information sharing, still carries a cracking risk.We propose a liquid crystal planar doublet as the information carrier, and new holograms generated by the new coupled phases when the relative displacements of the different liquid crystal layers change.The designed geometrical phases are generated by an optimized iterative restoration algorithm, and each holographic image formed by these phases is readable.This scheme achieves an increase in the capacity of the stored secret information and provides more misdirection, which is expected to have potential value in optical steganography and storage.
The hologram, which is formed by phases coupled through cascade devices for secret information sharing, still carries a cracking risk.We propose a liquid crystal planar doublet as the information carrier, and new holograms generated by the new coupled phases when the relative displacements of the different liquid crystal layers change.The designed geometrical phases are generated by an optimized iterative restoration algorithm, and each holographic image formed by these phases is readable.This scheme achieves an increase in the capacity of the stored secret information and provides more misdirection, which is expected to have potential value in optical steganography and storage.
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.
Photon plays a dominant role as the information carrier in telecom, thanks to the merits of large bandwidth and low energy consumption. Optical encryption has kept attracting intensive attention in the era of frequent information exchange. Multidegrees of light facilitate enhancing the security of data transmission. Here, following the Malus law and the phase encoding rule of the geometric phase, dual-channel intensities and a far-field hologram of the transmitted light are separately programmed. Different quick response codes that link to plaintexts are recorded into two intensity channels. They are further transformed according to the predetermined rule as revealed by the hologram to form the key. The key converts the protected information in a single-pixel imaging process, and generated ciphertexts are inserted into the plaintexts to perform the encryption. The tri-channel liquid crystal device enables simultaneous encryption in two separate routes and significantly improves information security. The design supplies a universal key for data encryption.
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.
A secret sharing scheme is an important cryptographic procedure that enables the secure distribution of secret information, such as private images, in an untrusted network. However, in all secret sharing schemes, the sizes of the shares increase in proportion to the size of the secret information, because they involve computationally expensive polynomials of degreen−1(n is total number of shares) and increasingly large modulus of modulo operations for security. Moreover, with large share sizes, it is not easy in practice to encrypt them quickly using block cipher algorithms. Therefore, ensuring the security of secret sharing for large-scale visual data with a reasonable share length and efficiently encrypting n shares properly represents formidable challenges. To overcome these challenges in secret sharing schemes, we propose new multiparty random phase wrapping secret sharing systems for visual datasets. Computational optical imaging enables the acquisition of wrapped phase information, ranging from –$\pi to\pi $, to be expressed in the form of a complex sinusoidal waveform. The proposed scheme allows for large-scale secret data—such as confidential digital images and visual data, including optical images—to be securely and efficiently shared and distributed to multiple parties or agencies utilizing a digital representation of a complex sinusoidal waveform of the secret information. The proposed scheme can be useful in cryptographic key escrow systems and in use with large-scale secret data.
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.
Abstract Recent progress in multidimensional multiplexing offers promising paths for next‐generation optical encryption. However, challenges remain in integration, dimensional expansion, and dynamic tunability. Here, a highly integrated optical encryption strategy is proposed that achieves 8‐channel multiplexing by combining polarization, wavelength, and spatial position within a single liquid crystal (LC) element, greatly increasing information capacity in a compact format. A multi‐layered nested encryption scheme is constructed, where plaintext is first encoded into a password‐protected quick response (QR) code. Decryption involves extracting far‐field holographic keys via wavelength and position, followed by Rivest–Shamir–Adleman (RSA) decryption and 26‐base preprocessing, and finally combining with polarization‐decoded data to retrieve the QR password and recover the plaintext. This hybrid scheme merges physical multiplexing with algorithmic decryption, enhancing both complexity and security. Additionally, the electro‐optical tunability of LCs adds an extra layer of security by allowing on‐demand encryption modulation. The proposed element demonstrates multifunctionality, high integration, and structural simplicity, showing strong potential for secure and scalable applications in optical encryption.