Parallel dynamic optical encryption based on light diffraction

Haoyang Yu, Min Ouyang, Xin Zhang +2 more

Xiangxin Xu, Jun Chang, Chuhan Wu +1 more

Most of the existing selective encryption schemes are based on image processing and cannot be realized by optical structures, so their practicality is limited. Combining the optical design, a local hybrid optical encryption system based on double random phase encoding is proposed. The system proposed in this paper possesses a common aperture and dual optical path structure, which is widely used in optical design and can effectively improve the practicality of optical encryption system. First, important information and non-important information in the original image are separated by a selective beam splitter. Then light waves carrying important information enter into the 4f system for encryption, and light waves carrying non-important information enter into the diffraction system for encryption. Finally, part of the diffraction system ciphertext is replaced with 4f system ciphertext to obtain the final encrypted image. Decryption is the reverse process of encryption. First, the 4f system ciphertext is cut out from the final ciphertext. Then the 4f system ciphertext is used to restore the information replaced in the diffraction system ciphertext, thereby obtaining the complete diffraction system ciphertext. Finally, the two ciphertexts go through the reverse process of their respective systems to complete the decryption. By comparing the statistical characteristics and mean square error of the original image and the encrypted image, the effectiveness of the proposed system's encryption process is proved. By analyzing the peak signal-to-noise ratio of the original image and the decrypted image, the effectiveness of the proposed system's decryption process is proved. The sensitivity of each key of the system is analyzed to prove the security of the system. Especially the system is highly sensitive to selective encryption key, which proves the effectiveness and security of the proposed system for selective encryption. Through simulation, it is verified that the proposed system is very resistant to diffraction attacks. Even if he can obtain all the diffraction keys, the attacker still cannot obtain the selectively encrypted information. Finally, through simulation, it is verified that the proposed system has good noise resistance and crop resistance, and high robustness as well. The proposed system can realize the selective encryption through optical structure, which is safe, effective and highly robust, and thus improving the practicality of selective optical encryption system.

Silvano Donati, ANNOVAZZI-LODI Valerio ANNOVAZZI-LODI Valerio, 王昭 Wang Zhao

Черёмхин Павел Аркадьевич, Nikolay N. Evtikhiev, Vitaly V Krasnov +4 more

The majority of contemporary optical encryption techniques use coherent illumination and suffer from speckle-noise pollution, which severely limits their applicability even when information encoded into special "containers" such as a QR code. Spatially incoherent encryption does not have this drawback, but it suffers from reduced encryption strength due to formation of an unobscured image right on top of the encrypted one by undiffracted light from the encoding diffraction optical element (DOE) in axial configuration. We present a new lensless encryption scheme, experimentally implemented with two liquid crystal spatial light modulators, that does not have this disadvantage because of a special encoding DOE design, which forms desired light distribution in the photosensor plane under spherically diverging illumination without a converging lens. Results of optical experiments on encryption of QR codes and successful information retrieval from decoded images are presented. Conducted analysis of encryption strength demonstrates sufficiently high key sensitivity and large enough key space to resist any brute force attacks.

Yanqiu Li, Lei Zheng, Reinhard Caspary +1 more

We propose an optical information encryption approach using azimuth multiplexing, encoding images in cascaded Diffractive Optical Elements (DOEs) with different rotation angles. While the approach works well in simulations, its experimental realization is challenging due to the sensitivity to positional shifts in DOEs. We aim to overcome these issues by enhancing shift tolerance. In this work, four different patterns were encrypted into cascaded DOEs designed using the proposed algorithm. The encrypted pattern can be correctly decrypted when the rotation angle of the first DOE is shifted by 0.5°from the designed rotation angle, indicating that it has a large shift tolerance. This approach is expected to facilitate the experimental realization of the complex optical image encryption system which will be tackled in the next step.

Unnikrishnan Gopinathan, David S. Monaghan, Thomas J. Naughton +1 more