El procesamiento de la información por medios opticos ha mostrado un gran potencial en su aplicación al campo de la seguridad. Las técnicas de cifrado y autenticación óptica aprovechan la capacidad de procesamiento en paralelo, alta velocidad de cómputo y también, la gran variedad de parámetros fisicos controlables que brindan Ios sistemas de procesamiento optico, lo que permite obtener sistemas con un alto grado de seguridad. La investigacion aqui desarrollada se centra, fundamentalmente, en el diseño y desarrollo de sistemas optico-digitales de seguridad basados en la arquitectura del correlador de transformada conjunta (Joint Transform Correlator, JTC). Los sistemas de seguridad presentados en esta tesis son de cifrado y autenticacion de la informacion. Los sistemas de cifrado propuestos, se caracterizan por ser sistemas optico-digitales no lineales, sencillos, que cubren un doble proposito: primero, una calidad de imagen descifrada mejorada con respecto a otros sistemas de cifrado de tecnologia similar y segundo, un alto de grado de seguridad, ya que disponen de varias llaves y son resistentes a varios ataques de seguridad. Estas caracteristicas son obtenidas gracias al diseño del sistema cifrador basado en la arquitectura JTC en diversos dominios de procesamiento optico, tales como Ios dominios de: Fourier, Fresnel y Fraccionario de Fourier. En este trabajo, tambien se incluye una validacion experimental de Ios aspectos mas basicos del sistema cifrador propuesto. Finalmente, se presenta una integracion de la tecnica de conteo de fotones en el sistema cifrador basado en un JTC, con el fin de autenticar y verificar una imagen primaria (por ejemplo, una imagen de una huella dactilar) y un codigo de fase aleatorio, respectivamente, de forma segura y simultanea. La inclusion de la tecnica de conteo de fotones en el sistema de procesamiento de la informacion incrementa la seguridad del sistema cifrador y tambien, hace que el sistema de autenticaci6n sea mas robusto en contra de ataques no autorizados.
The multifactor optical encryption authentication method [Opt. Lett., 31 721-3 (2006)] reinforces optical security by allowing the simultaneous authentication of up to four factors. In this work, the photon-counting imaging technique is applied to the multifactor encrypted function so that a sparse phase-only distribution is generated for the encrypted data. The integration of both techniques permits an increased capacity for signal hiding with simultaneous data reduction for better fulfilling the general requirements of protection, storage and transmission. Cryptanalysis of the proposed method is carried out in terms of chosen-plaintext and chosen-ciphertext attacks. Although the multifactor authentication process is not substantially altered by those attacks, its integration with the photon-counting imaging technique prevents from possible partial disclosure of any encrypted factor, thus increasing the security level of the overall process. Numerical experiments and results are provided and discussed.
We propose a generalization of the encryption system based on double random phase encoding (DRPE) and a joint transform correlator (JTC), from the Fourier domain to the fractional Fourier domain (FrFD) by using the fractional Fourier operators, such as the fractional Fourier transform (FrFT), fractional traslation, fractional convolution and fractional correlation. Image encryption systems based on a JTC architecture in the FrFD usually produce low quality decrypted images. In this work, we present two approaches to improve the quality of the decrypted images, which are based on nonlinear processing applied to the encrypted function (that contains the joint fractional power spectrum, JFPS) and the nonzero-order JTC in the FrFD. When the two approaches are combined, the quality of the decrypted image is higher. In addition to the advantages introduced by the implementation of the DRPE using a JTC, we demonstrate that the proposed encryption system in the FrFD preserves the shift-invariance property of the JTC-based encryption system in the Fourier domain, with respect to the lateral displacement of both the key random mask in the decryption process and the retrieval of the primary image. The feasibility of this encryption system is verified and analyzed by computer simulations.
A new optical security system for image encryption based on a nonlinear joint transform correlator (JTC) in the Fresnel domain (FrD) is proposed. The proposal of the encryption process is a lensless optical system that produces a real encrypted image and is a simplified version of some previous JTC-based encryption systems. We use a random complex mask as the key in the nonlinear system for the purpose of increasing the security of the encrypted image. In order to retrieve the primary image in the decryption process, a nonlinear operation has to be introduced in the encrypted function. The optical decryption process is implemented through the Fresnel transform and the fractional Fourier transform. The security system proposed in this paper preserves the shift-invariance property of the JTC-based encryption system in the Fourier domain, with respect to the lateral displacement of the key random mask in the decryption process. This system shows an improved resistance to chosen-plaintext and known-plaintext attacks, as they have been proposed in the cryptanalysis of the JTC encrypting system. Numerical simulations show the validity of this new optical security system. (C) 2014 Optical Society of America
A new optical security system for image encryption based on a fractional joint transform correlator and nonlinear filtering is proposed. The position of the lens in the proposed optical encryption setup can be chosen, so that an additional key is introduced in the security system. The distributions at the input and output planes of the encryption system are related by a fractional Fourier transform (FrFT) at a given fractional order that is defined, among other parameters, by the focal length and the position of the lens in the setup; this fractional order acts as an additional key of the security system. The optical intensity of the complex distribution in the fractional Fourier domain (output plane) is captured by a CCD camera. The nonlinearity introduced in the last step of the encryption process, maintains the encrypted function as a real-valued function. The security system proposed in this work is an generalization of the encryption system based on a conventional joint transform correlator (JTC), from the Fourier domain to the fractional Fourier domain. Additional advantages of the proposed system are: new degrees of freedom for the optical setup, alleviated alignment requirement, and the introduction of an additional key (the fractional order of the FrFT) that improves security. Numerical simulations verify the validity of this new optical security system
Vilardy, J.; Millan, M.; Pérez-Cabré, E. Iberoamerican Conference on Optics, Latinamerican meeting on Optics Lasers and Applications p. 87853O-1-87853O-8 DOI: 10.1117/12.2020913 Presentation's date: 2013-07-21 Presentation of work at congresses
A SLM has been experimentally characterized in terms of amplitude modulation versus the gray level distribution (input signal) electronically addressed to the pixelated display in two conditions: input constant with time, and time variant input with increasing frame rate. The SLM considered in this work was a twisted nematic liquid
crystal display manufactured by CRL (XGA2 model) that operates on the transmitted light. The influence of some technical specications such as gamma correction, brightness and contrast of this SLM have been considered as well.
Vilardy, J.; Millan, M.; Pérez-Cabré, E. Iberoamerican Conference on Optics, Latinamerican meeting on Optics Lasers and Applications DOI: 10.1117/12.2020912 Presentation's date: 2013-07 Presentation of work at congresses
A new optical security system for image encryption based on a nonlinear joint transform correlator (JTC) and Fresnel transform is proposed. A lensless optical encryption system, which is a simplifried version of previous JTCbased encryption systems, produces a complex distribution in the Fresnel domain, whose intensity is captured by a power-law sensor and nonlinearly modified to yield the real-valued encrypted image. The nonlinearity plays an essential role in the decryption system which, in turn, contains an optical fractional Fourier transform to retrieve the primary image. The security system proposed in this work is a novel extension of the conventional JTC-based encryption system from the Fourier domain to the Fresnel domain. Additional advantages of the proposed system are: simplification of the optical setup, alleviated alignment requirements, and an additional key (the propagation distance) that improves security. Numerical simulations verify the validity of this new optical security system.
Millan, M.; Pérez-Cabré, E.; Romero, L.; Ramirez, N. Iberoamerican Conference on Optics, Latinamerican meeting on Optics Lasers and Applications DOI: 10.1117/12.2025472 Presentation's date: 2013-07 Presentation of work at congresses
Pixelated liquid crystal displays have been widely used as spatial light modulators to implement programmable diffractive optical elements (DOEs), particularly diffractive lenses. Many different applications of such components have been developed in information optics and optical processors that take advantage of their properties of great flexibility, easy and fast refreshment, and multiplexing capability in comparison with equivalent conventional refractive lenses. In this paper, we explore the application of programmable diffractive lenses displayed on the pixelated screen of a liquid crystal on silicon spatial light modulator (LCoS-SLM) to ophthalmic optics. In particular, we consider the use of programmable diffractive lenses for the visual compensation of some refractive errors (myopia, hyperopia). The theoretical principles of compensation are described and sketched using geometrical optics and paraxial ray tracing. A series of experiments with artificial eye in optical bench are conducted to analyze the compensation accuracy in terms of optical power and to compare the results with those obtained by means of conventional ophthalmic lenses. Practical considerations oriented to feasible applications are provided.
In the approach of geometrical optics, ray tracing is an illustrative tool to determine the light path through an optical system. We show different educational resources used to help students to develop their skills in
graphical ray tracing.