Information security and authentication are important challenges facing society. Recent attacks by hackers on the databases of large commercial and financial companies have demonstrated that more research and development of advanced approaches are necessary to deny unauthorized access to critical data. Free space optical technology has been investigated by many researchers in information security, encryption, and authentication. The main motivation for using optics and photonics for information security is that optical waveforms possess many complex degrees of freedom such as amplitude, phase, polarization, large bandwidth, nonlinear transformations, quantum properties of photons, and multiplexing that can be combined in many ways to make information encryption more secure and more difficult to attack. This roadmap article presents an overview of the potential, recent advances, and challenges of optical security and encryption using free space optics. The roadmap on optical security is comprised of six categories that together include 16 short sections written by authors who have made relevant contributions in this field. The first category of this roadmap describes novel encryption approaches, including secure optical sensing which summarizes double random phase encryption applications and flaws [Yamaguchi], the digital holographic encryption in free space optical technique which describes encryption using multidimensional digital holography [Nomura], simultaneous encryption of multiple signals [Perez-Cabre], asymmetric methods based on information truncation [Nishchal], and dynamic encryption of video sequences [Torroba]. Asymmetric and one-way cryptosystems are analyzed by Peng. The second category is on compression for encryption. In their respective contributions, Alfalou and Stern propose similar goals involving compressed data and compressive sensing encryption. The very important area of cryptanalysis is the topic of the third category with two sections: Sheridan reviews phase retrieval algorithms to perform different attacks, whereas Situ discusses nonlinear optical encryption techniques and the development of a rigorous optical information security theory. The fourth category with two contributions reports how encryption could be implemented at the nano- or micro-scale. Naruse discusses the use of nanostructures in security applications and Carnicer proposes encoding information in a tightly focused beam. In the fifth category, encryption based on ghost imaging using single-pixel detectors is also considered. In particular, the authors [Chen, Tajahuerce] emphasize the need for more specialized hardware and image processing algorithms. Finally, in the sixth category, Mosk and Javidi analyze in their corresponding papers how quantum imaging can benefit optical encryption systems. Sources that use few photons make encryption systems much more difficult to attack, providing a secure method for authentication.

http://diposit.ub.edu/dspace/bitstream/2445/118388/1/664334.pdf

Roadmap on optical security

On the verge of the 50th anniversary of Vander Lugt’s formulation for pattern matching based on matched filtering and optical correlation, we acknowledge the very intense research activity developed in the field of correlation-based pattern recognition during this period of time. The paper reviews some domains that appeared as emerging fields in the last years of the 20th century and have been developed later on in the 21st century. Such is the case of three-dimensional (3D) object recognition, biometric pattern matching, optical security and hybrid optical–digital processors. 3D object recognition is a challenging case of multidimensional image recognition because of its implications in the recognition of real-world objects independent of their perspective. Biometric recognition is essentially pattern recognition for which the personal identification is based on the authentication of a specific physiological characteristic possessed by the subject (e.g. fingerprint, face, iris, retina, and multifactor combinations). Biometric recognition often appears combined with encryption–decryption processes to secure information. The optical implementations of correlation-based pattern recognition processes still rely on the 4f-correlator, the joint transform correlator, or some of their variants. But the many applications developed in the field have been pushing the systems for a continuous improvement of their architectures and algorithms, thus leading towards merged optical–digital solutions.

http://iopscience.iop.org/article/10.1088/2040-8978/14/10/103001/pdf

Advanced optical correlation and digital methods for pattern matching—50th anniversary of Vander Lugt matched filter

Phase image encryption in the fractional Hartley domain using Arnold transform and singular value decomposition

The integration of photon-counting imaging techniques and optical encryption systems can improve information authentication robustness against intruder attacks. Photon-counting imaging generates distributions with far fewer photons than conventional imaging and provides substantial bandwidth reduction by generating sparse encrypted data. We show that photon-limited encrypted distributions have sufficient information for successful decryption, authentication and signal retrieval. Additional compression of the encrypted distribution is applied by limiting the number of phase values used to reproduce the phase information of the complex-valued encrypted data. The validity of this technique—with and without phase compression—is probed through simulated experiments for two types of input images: alphanumerical signs and dithered natural scenes.

/pdf/photon-counting-double-random-phase-encoding-for-secure-568onwkty5.pdf

Photon-counting double-random-phase encoding for secure image verification and retrieval

Some image encryption systems based on modified double random phase encoding and joint transform correlator architecture produce low quality decrypted images and are vulnerable to a variety of attacks. In this work, we analyse the algorithm of some reported methods that optically implement the double random phase encryption in a joint transform correlator. We show that it is possible to significantly improve the quality of the decrypted image by introducing a simple nonlinear operation in the encrypted function that contains the joint power spectrum. This nonlinearity also makes the system more resistant to chosen-plaintext attacks. We additionally explore the system resistance against this type of attack when a variety of probability density functions are used to generate the two random phase masks of the encryption–decryption process. Numerical results are presented and discussed.

/pdf/improved-decryption-quality-and-security-of-a-joint-b7y6fqytya.pdf

Improved decryption quality and security of a joint transform correlator-based encryption system

Optical Data Encryption

espanolLa Correlacion Nolineal Dual (DNC) es una operacion general en reconocimiento optico de patrones en la que el preprocesado nolineal introducido en el canal de referencia puede diferir del introducido en el canal de entrada. Abarca un gran numero de metodos de filtrado lineal y nolineal y puede realizarse mediante un correlador optoelectronico de transformadas conjuntas (JTC) en dos pasos. La capacidad del sistema depende finalmente de algunas condiciones experimentales tales como la discretizacion, el rango dinamico de niveles de gris, la saturacion y otras caracteristicas tecnicas de la camara y el modulador utilizados en el JTC. En este trabajo, presentamos una revision de las tecnicas de reconocimiento basadas en la DNC, centrandonos en primer lugar en la descripcion de los fundamentos, las propiedades y la realizacion optica de la correlacion nolineal dual. Las posibilidades de la DNC en el reconocimiento de patrones con sensibilidad ajustable se presentan en un segundo trabajo (K. Chalasinska-Macukow et al., ? Dual Nonlinear Correlation in Optical Pattern Recognition II, Optica Pura y Aplicada 38, num. 2, 85- 97, 2005). EnglishDual Nonlinear Correlation (DNC) is a general operation in optical pattern recognition where the nonlinear pre-processing introduced in the reference channel may differ from that introduced in the input channel. It involves a number of popular linear and nonlinear filtering methods and can be implemented by an optoelectronic two-step joint transform correlator (JTC). The eventual capabilities of the system depend on some experimental conditions such as quantization, greylevel dynamic range, saturation, and other technical characteristics of both the camera and the spatial light modulator used in the JTC. An overview of the pattern recognition techniques based on DNC is presented in this paper. Firstly, we focus our attention on the description of the principle, properties and optical implementation of the dual nonlinear correlation. The potential of DNC to achieve pattern recognition with adjustable sensitivity is presented in a second work (K. Chalasinska-Macukow et al.,” Dual Nonlinear Correlation in Optical Pattern Recognition II, Optica Pura y Aplicada 38, num. 2, 85-97, 2005).

La Correlación Nolineal Dual en el Reconocimiento Óptico de Patrones (I): Principio y Realización Optoelectrónica.

espanolEl modelo de la Correlacion Nolineal Dual (DNC), realizable mediante un correlador optoelectronico de transformadas conjuntas (JTC) (Millan et al., Dual Nonlinear Correlation in Optical Pattern Recognition I, Optica Pura y Aplicada 38, num. 2, 75-83, 2005), proporciona un sistema de reconocimiento de patrones con capacidad de discriminacion (DC) ajustable. Variando los valores de dos parametros reales (L y M) en la DNC obtenemos bien un incremento de la DC, o bien una cierta tolerancia ante variaciones de forma y de nivel de gris respecto al objeto de referencia. Diversas aplicaciones del metodo se extienden al reconocimiento de objetos en color mediante la correlacion multicanal. Limitando la region de soporte en el dominio de frecuencias de los espectros de transformadas conjuntas modificados, y variando los valores de L y M, se obtiene un sistema de reconocimiento con DC variable segun la textura y la forma. Se presentan y analizan resultados de simulacion y experimentales. EnglishThe Dual Nonlinear Correlation (DNC) model implemented by an optoelectronic joint transform correlator (JTC) (Millan et al., Dual Nonlinear Correlation in Optical Pattern Recognition I, Optica Pura y Aplicada 38, num. 2, 75-83, 2005) provides a pattern recognition system with adjustable discrimination capability (DC). By varying the values of two real parameters (L and M) in the DNC we obtain either an increase or a relaxation of the DC for shape or grey level variations with respect to the reference object. Diverse applications of the method are extended to colour pattern recognition by multichannel correlation. By limiting the region of support in the frequency domain of the modified joint power spectra and varying the L and M values, we obtain pattern recognition with variable DC to texture and shape. Simulated and experimental results are presented and discussed.

La Correlación Nolineal Dual en el Reconocimiento Óptico de Patrones (II): Reconocimiento con Sensibilidad Ajustable.

espanolLa caracterizacion optica de las lentes intraoculares (IOLs del ingles Intraocular Lenses) proporciona una informacion objetiva y cuantitativa que es necesaria para comprender su funcionamiento como implante que sustituye al cristalino en el sistema visual humano. Ademas, permite predecir el rendimiento de los nuevos disenos. Dicha caracterizacion se debe llevar a cabo mediante pruebas in vivo en pacientes ya implantados, asi como con pruebas in vitro en banco optico o mediante simulacion teorica. La tesis comienza con un analisis de las fuentes de error en el calculo de la potencia de las lentes intraoculares y explora la posible compensacion de los errores refractivos residuales mediante el uso de grados de libertad no convencionales. Se centra, fundamentalmente, en la caracterizacion in vitro de una variedad de lentes comercialmente disponibles (monofocales, multifocales, esfericas, asfericas, apodizadas, no-apodizadas, y distintos materiales, potencias y adiciones) en un banco optico. Para ello se han disenado y puesto a punto los metodos de medida y un montaje experimental que reproduzca las condiciones en las que las lentes se implantan en el ojo de acuerdo con la normativa internacional. Se ha desarrollado e implementado un metodo para la cuantificacion experimental de la eficiencia energetica de los distintos modelos de IOLs. Este metodo ha servido para explicar algunos resultados clinicos obtenidos al evaluar la vision estereoscopica con dos tests con diferente principio de funcionamiento. Se ha medido la calidad optica basicamente a traves de la Funcion de Transferencia de Modulacion. Se ha desarrollado e implementado un metodo para caracterizar el halo que perciben algunos pacientes implantados con IOLs multifocales. Finalmente, los resultados experimentales se han utilizado para comparar el rendimiento de las IOLs entre ellas. EnglishThe optical characterization of an intraocular lens (IOL) provides objective and quantitative information that is essential to fully understand its performance as an implant that replaces the crystalline lens in the human visual system. Additionally, it can be used to predict the performance of the new IOL designs. This characterization has to be carried out using in vivo tests in implanted patients and in vitro, by means of an optical bench or theoretical simulations. This thesis begins with an analysis of the main sources of uncertainty in the calculation of the IOL power and explores the compensation of the residual refractive errors by using some unconventional degrees of freedom. The thesis focuses on the in vitro characterization of a variety of commercially available IOLs (monofocal, multifocal, spherical, aspherical, apodized, full-aperture, and of different materials, powers and additions) in optical bench. To this end, we have designed and implemented the necessary methods of measurement and an experimental setup that, according to the international standard regulation, reproduces the conditions of such implants in the human eye. We have developed a method to measure the energy efficiency of IOLs. This method has allowed us to explain the clinical results obtained in the evaluation of the stereoscopic acuity when using two tests based on different principles. The optical imaging quality of IOLs has been basically quantified through the experimental measurement of the modulation transfer function. We have developed and implemented a method to characterize some artefact, named halo, which can be perceived by those patients implanted with multifocal IOLs. Finally, all the experimental results have been used as a basis for the inter-class comparison of the IOL performances

Optical Characterization of Intraocular Lenses

espanolLas muestras de un atlas de color pueden experimentar variaciones en su color de referencia, dependiendo de su antiguedad, estado de conservacion, uso, etc. En este trabajo medimos las diferencias de color existentes entre pares de muestras que tienen la misma especificacion pero que pertenecen a dos libros distintos del atlas de color Munsell. Utilizamos un espectrorradiometro para medir el color bajo iluminacion D65. Calculamos las diferencias de color en las metricas CIELAB y CIEDE2000 y las comparamos con otras distancias: el error instrumental y la diferencia de color de cada una de las muestras del par con sus vecinos mas proximos dentro de la propia coleccion a la que pertenece. El estudio se realiza sobre los ejemplares de dos libros Munsell de muestras mate: la coleccion de colores casi neutros (Nearly Neutral Munsell Collection) y el libro de colores (Munsell Book of Colours). Las diferencias de color llegan a alcanzar 1 unidad CIELAB en las muestras de la region del amarillo. EnglishA colour chart consists of a collection of patches whose reference colour may vary depending on their age, keeping conditions, use, etc. In this work we measure the colour differences between sample pairs with the same specification but belonging to two individual books of the Munsell chart. A spectroradiometer is used for colour measurements under D65 illumination and CIELAB and CIEDE2000 metrics are considered for colour difference calculation. The colour differences are then compared with other distances: the instrumental uncertainty and the colour differences between each pair sample and their respective nearest neighbour samples within the particular collection to which they belong. The study is carried out on two individual Munsell books of matte colour samples: the Nearly Neutral Munsell Collection and the Munsell Book of Colours. The colour differences reach one unity CIELAB in the case of patches belonging to the yellow colour region.

María Sagrario Millán García-Varela

Papers

Optical Data Encryption

La Correlación Nolineal Dual en el Reconocimiento Óptico de Patrones (I): Principio y Realización Optoelectrónica.

La Correlación Nolineal Dual en el Reconocimiento Óptico de Patrones (II): Reconocimiento con Sensibilidad Ajustable.

Optical Characterization of Intraocular Lenses

Diferencias de color entre dos ejemplares de un mismo atlas de color.