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Laser Physics Letters

QR code optical encryption using spatially incoherent illumination

Черёмхин Павел Аркадьевич, Vitaly V Krasnov, Vladislav G. Rodin, Rostislav S. Starikov

Published Jan 9, 2017• 46 citations
Publisher

Abstract

Abstract Optical encryption is an actively developing field of science. The majority of encryption techniques use coherent illumination and suffer from speckle noise, which severely limits their applicability. The spatially incoherent encryption technique does not have this drawback, but its effectiveness is dependent on the Fourier spectrum properties of the image to be encrypted. The application of a quick response (QR) code in the capacity of a data container solves this problem, and the embedded error correction code also enables errorless decryption. The optical encryption of digital information in the form of QR codes using spatially incoherent illumination was implemented experimentally. The encryption is based on the optical convolution of the image to be encrypted with the kinoform point spread function, which serves as an encryption key. Two liquid crystal spatial light modulators were used in the experimental setup for the QR code and the kinoform imaging, respectively. The quality of the encryption and decryption was analyzed in relation to the QR code size. Decryption was conducted digitally. The successful decryption of encrypted QR codes of up to 129 × 129 pixels was demonstrated. A comparison with the coherent QR code encryption technique showed that the proposed technique has a signal-to-noise ratio that is at least two times higher.

DOI
10.1088/1612-202x/aa5242

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Abstract Optical encryption is an actively developing field of science. The majority of encryption techniques use coherent illumination and suffer from speckle noise, which severely limits their applicability. The spatially incoherent encryption technique does not have this drawback, but its effectiveness is dependent on the Fourier spectrum properties of the image to be encrypted. The application of a quick response (QR) code in the capacity of a data container solves this problem, and the embedded error correction code also enables errorless decryption. The optical encryption of digital information in the form of QR codes using spatially incoherent illumination was implemented experimentally. The encryption is based on the optical convolution of the image to be encrypted with the kinoform point spread function, which serves as an encryption key. Two liquid crystal spatial light modulators were used in the experimental setup for the QR code and the kinoform imaging, respectively. The quality of the encryption and decryption was analyzed in relation to the QR code size. Decryption was conducted digitally. The successful decryption of encrypted QR codes of up to 129 × 129 pixels was demonstrated. A comparison with the coherent QR code encryption technique showed that the proposed technique has a signal-to-noise ratio that is at least two times higher.
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.
State of the art micromirror DMD spatial light modulators (SLM) offer unprecedented frame rate of up to 32000 frames per second. This, in conjunction with fast digital camera, makes it possible to create high speed optical encryption systems. Experimental setup for optical encryption under spatially incoherent illumination based on two DMD SLMs had been created. Input information is displayed by first SLM, encoding hologram - by second SLM. Results of optical experiment demonstrate successful encryption and decryption of digital information in the form of QR code image.
Abstract Exclusive-OR (XOR) operation is a popular technique in optical cryptography. The linear and inverse properties of XOR operation provide a simple way of encryption but in some cases fail to provide strong security. In XOR-based image encryption, each pixel is individually encrypted, therefore secret information can be traced with partial knowledge of the key. In this paper, we describe a simple and practical method to improve the strength and effectiveness of XOR-based encryption. A higher level of security is achieved by implementing a phase retrieval algorithm with XOR operation. Another advantage of the proposed scheme is that the optical XOR operation is demonstrated using incoherent light sources, which make the system compact, speckle free, and cost effective. Also, to overcome the problem of quality degradation while decrypting, quick response code-based ciphertext has been implemented. Both simulation and experimental results are demonstrated as a proof-of-concept.
Abstract Coherent optical encryption procedures introduce speckle noise to the output, limiting many practical applications. Until now the only method available to avoid this noise is to codify the information to be processed into a container that is encrypted instead of the original data. Although the decrypted container presents the noise due to the optical processing, their features remain recognizable enough to allow decoding, bringing the original information free of any kind of degradation. The first adopted containers were the quick response (QR) codes. However, the limitations of optical encryption procedures and the features of QR codes imply that in practice only simple codes containing small amounts of data can be processed without large experimental requirements. In order to overcome this problem, we introduce the first tailor made container to be processed in optical cryptosystems, ensuring larger noise tolerance and the ability to process more information with less experimental requirements. We present both simulations and experimental results to demonstrate the advantages of our proposal.
In holographic encryption, double random-phase encoding in the Fresnel domain (DRPEiFD) is a prevalent encryption method because it is lensless and secure.However, noises bring adverse effects during decryption.In this letter, we introduce quick-response (QR) coding during encryption to resist noises.We transform the original information into a QR code and then encrypt the code as a hologram through DRPEiFD.To retrieve the input, we decrypt the hologram in the opposite manner to the encryption and subsequently obtain a QR code with noises.By scanning this code with proper applications in smartphones, we can obtain a noise-free retrieval.Numerical experiments and images scanned by a smartphone are shown to validate our proposed method.