Research On Optical Encryption Technology Based On Scattering Media

With the rapid development of computer and Internet technology,information globalization has become a crucial feature of nowadays world,as a result,the importance of information security has become increasingly prominent.Therefore,how to encrypt information quickly and effectively has become a hot issue in current information processing research.Optical encryption technology is a novel information security processing technology,which has been developing in recent 20 years.Since it provides the possibility of high-speed and parallel processing of 2D image data and hiding information of many different dimensions(multiple degrees of freedom),it has been widely concerned and studied by the academic community.Due to the scattering effect of the particles with the size of wavelength in the scattering medium on the incident light wave,the ordered wavefront phase in the incident light wave is intensely distorted,and the outgoing light field becomes random and disordered.Finally,only the speckle pattern "coded" by the scattering effect of scattering medium can be received on the observation surface after the incident light wave passing through the scattering medium.Consequently,it is arduous to observe and/or image the target which is covered or hidden by the scattering medium,and thus the scattering media is regarded as an obstacle in the traditional imaging field.In contrast,the optical encryption technology based on scattering media makes full use of the scattering effect of scattering media to transform the plaintext image to white noise-liked speckle pattern,thus realizing the encryption process from plaintext to ciphertext.Nevertheless,because the optical encryption technology based on scattering media is carried out within the optical memory effect of scattering encryption system,the autocorrelation of ciphertext is approximately equal to that of plaintext,which makes this kind of system vulnerable to ciphertext-only attack using phase retrieval algorithm,resulting in the security of the system greatly threatened.To solve this problem,for the first time,to the best of our knowledge,an optical encryption method based on the uncorrelated characteristics of scattering media is proposed,which can efficiently resist the ciphertext-only attack using phase retrieval algorithm.In addition,the proposed encryption system is of great security and flexibility.In term of the system security,we propose two ways to reduce the signal-to-noise ratio of ciphertext,which are adding artificial noise and introducing environmental broadband noise,so as to further enhance the resistance of the system to the ciphertext-only attack using phase retrieval algorithm.In term of system flexibility,an off-line encryption method for image information using the pre-recorded point spread functions is proposed.The main innovations of this article are as follows:(1)A novel optical encryption method utilizing the spatially or spectrally uncorrelated characteristics of artificial dynamic scattering media combined with random sampling is proposed,which solves the problem of ciphertext-only attacks using phase retrieval algorithm;(2)A novel optical encryption method using the structurally uncorrelated characteristics of the natural dynamic scattering media is proposed,which is capable of solving the problem of ciphertext-only attacks using the phase recovery algorithm,and further enhancing the encryption security;(3)A flexible method to realize the optical encryption of dynamic scattering media offline is proposed,which further simplifies the implementation process of the encryption scheme proposed above,making the implementation of the proposed method simpler,and easier to implement.This paper conducts research the following aspects:(1)In this paper,the fundamental principle of optical encryption is theoretically analyzed,the main methods of optical encryption are introduced,and the characteristics of various optical encryption methods are analyzed.To get rid of the attacks based on phase retrieval algorithms that are the most threatening to system security,a simple and easy-to-fabricate optical encryption method based on the uncorrelated characteristics of scattering media is proposed and demonstrated.This method is extremely powerful to resist to the ciphertext-only attack using phase retrieval algorithm.(2)The overall design scheme of the system is given,and then the specific encryption plan is given.The images are encrypted using the spatially uncorrelated characteristics,spectrally uncorrelated characteristics and structural uncorrelated characteristics of the scattering media;and the important components of the system are selected.Simple and flexible optical encryption systems are designed and built.(3)In this paper,the sensitivity of phase retrieval algorithm to noise compared with deconvolution algorithm is fully considered,a novel method to improve the system's ability to resist ciphertext-only attack by reducing the ciphertext SNR is proposed,in which the SNR of ciphertext can be reduced by artificially adding Gaussian noise or introducing broadband illumination.Experiments on encryption and decryption and simulated ciphertext-only attack are carried out to demonstrate the feasibility of the method.The flexible off-line encryption of plaintext image is proposed,in which the encrypted speckle ciphertext image can be obtained by performing simple convolution on plaintext image with pre-recorded point spread function key just using computer.The experiments of encryption and decryption and simulated ciphertext-only attack are carried out to verify the effectiveness of the proposed method.The research shows that the proposed optical encryption method based on the uncorrelated characteristics of scattering media can achieve high security encryption of images.It can effectively and efficiently resist the ciphertext-only attack using phase retrieval algorithm,which guarantees the high security.Meanwhile,the system is simple and flexible,and is capable of encrypting binary images as well as complex grayscale images,which provides a new idea for image and video information encryption.As a result,it is of great potential and promising prospects.