Entropic Inequalities for a Class of Quantum Secret Sharing States

It is well-known that von Neumann entropy is nonmonotonic unlike Shannon entropy (which is monotonically nondecreasing). Consequently, it is difficult to relate the entropies of the subsystems of a given quantum state. In this paper, we show that if we consider quantum secret sharing states arising from a class of monotone span programs, then we can partially recover the monotonicity of entropy for the so-called unauthorized sets. Furthermore, we can show for these quantum states the entropy of the authorized sets is monotonically nonincreasing.Comment: LaTex, 5 page

Controlled Data Sharing for Collaborative Predictive Blacklisting

Although sharing data across organizations is often advocated as a promising way to enhance cybersecurity, collaborative initiatives are rarely put into practice owing to confidentiality, trust, and liability challenges. In this paper, we investigate whether collaborative threat mitigation can be realized via a controlled data sharing approach, whereby organizations make informed decisions as to whether or not, and how much, to share. Using appropriate cryptographic tools, entities can estimate the benefits of collaboration and agree on what to share in a privacy-preserving way, without having to disclose their datasets. We focus on collaborative predictive blacklisting, i.e., forecasting attack sources based on one's logs and those contributed by other organizations. We study the impact of different sharing strategies by experimenting on a real-world dataset of two billion suspicious IP addresses collected from Dshield over two months. We find that controlled data sharing yields up to 105% accuracy improvement on average, while also reducing the false positive rate.Comment: A preliminary version of this paper appears in DIMVA 2015. This is the full version. arXiv admin note: substantial text overlap with arXiv:1403.212

Mapeo de Actores y Necesidades de Información Agroclimática en los Cultivos de Maíz y Frijol en sitios piloto - Colombia

Este trabajo presenta los resultados del mapeo de actores y necesidades de información agroclimática en los cultivos transitorios de seguridad alimentaria: maíz y frijol arbustivo en sitios piloto en Colombia. A través del mapeo de los actores que transmiten información a los agricultores, la confianza en la información proporcionada, y las necesidades de información para la toma de decisiones, logramos entender el ancho espectro de problemas y prioridades a tomar en cuenta en la producción de estos cultivos, y proponer soluciones útiles, relevantes, confiables, sostenibles y aplicables. Con este enfoque, se llevaron a cabo 27 entrevistas semi-estructuradas con informantes clave y 12 grupos focales con un total de 151 agricultores en los departamentos de Córdoba y Santander. Los resultados evidencian que una de las prioridades de los agricultores es recibir información agroclimática confiable a escala local, que permita tomar mejores decisiones de siembra, variedades, insumos y manejo de suelos y cultivos ante eventos de variabilidad climática. Se evidencia una desconfianza en las instituciones oficiales que transmiten información climática y un sentimiento difuso de falta de interés de las instituciones hacia los pequeños agricultores. Los agricultores se endeudan para lograr producir fríjol arbustivo y maíz o subsidian la producción por otros cultivos, mientras el acceso a un seguro agrícola es limitado. El formato preferido para recibir información climática es a través de mensajes de texto (celular) y mensajes en la radio local. Grupos de interacción presencial o virtual entre agricultores y expertos parecen una alternativa útil y confiable para recibir y compartir información en tiempo real. Sin embargo, los agricultores están interesados en adoptar el manejo agrícola tras un pronóstico si: a) la información es local, b) proviene de una fuente considerada confiable como expertos u otros agricultores, c) se transmite en el momento adecuado para la toma de decisiones y d) si sus efectos son medibles, verificables y validados, por ejemplo, a través de resultados de pilotos o parcelas experimentales en dos años consecutivos. ENGLISH This working paper presents the results of the mapping of actors and of agroclimatic information needs in pilot sites in Colombia for two annual crops, fundamental for food security: maize and bush beans. The mapping of the actors that transmit information to farmers, the confidence the latter have in the information provided, and their information needs for decision-making, allows us to understand the broad spectrum of issues and priorities to be taken into account in the production of these crops, and suggest solutions that are useful, relevant, reliable, sustainable and applicable. Under this assumption, we conducted 27 semi-structured interviews with key informants and 12 focus groups with a total of 151 farmers in the departments of Córdoba and Santander. Results show that one of the priorities of farmers is to receive reliable local agroclimatic information that enables them to take decisions on planting, varieties, inputs, soil and crop management, that address climate variability. We find a generalized distrust of official institutions that transmit weather information, and a feeling that institutions are not interested in smallholders. Farmers resort to indebtedness to produce beans and maize, or subsidize production with cash crops, while access to agricultural insurance is limited. The format preferred to receive weather information is text messages (phone) and information through the local radio. The creation of groups of farmers and experts who interact in person or virtually seem a useful and reliable alternative to receive and share information in real time. However, farmers are only interested in adopting farm management changes after a forecast if: a) the information is local, b) the information is given by a trusted source such as experts or other farmers, c) the information is transmitted at the right time for decision-making d) the effects of taking these decisions are measurable, verifiable and validated, for example, through pilots or results from experimental plots in two consecutive years

ESSVCS: an enriched secret sharing visual cryptography

Visual Cryptography (VC) is a powerful technique that combines the notions of perfect ciphers and secret sharing in cryptography with that of raster graphics. A binary image can be divided into shares that are able to be stacked together so as to approximately recover the original image. VC is a unique technique in the sense that the encrypted message can be decrypted directly by the Human Visual System (HVS). The distinguishing characteristic of VC is the ability of secret restoration without the use of computation. However because of restrictions of the HVS, pixel expansion and alignment problems, a VC scheme perhaps can only be applied to share a small size of secret image. In this paper, we present an Enriched Secret Sharing Visual Cryptography Scheme (ESSVCS) to let the VC shares carry more secrets, the technique is to use cypher output of private-key systems as the input random numbers of VC scheme, meanwhile the encryption key could be shared, the shared keys could be associated with the VC shares. After this operation, VC scheme and secret sharing scheme are merged with the private-key system. Under this design, we implement a (k; t; n)-VC scheme. Compared to those existing schemes, our scheme could greatly enhance the ability of current VC schemes and could cope with pretty rich secrets

Local, reliable and timely agro-climatic information: a requirement of Colombian farmers

Awareness of climatic information relevant for future decisions through climatic forecasts is not enough to support farmer’s decision-making. It is necessary to look for agricultural management alternatives that allow farmers to adapt to climatic conditions and implement efficient and sustainable management systems, within a framework of effective communication with farmers (Jones, 2003; Pulwarty et al., 2003). In Latin America are very few the initiatives related to climatic forecasts. The Project “Agroclimatic services and food security information for improved decision-making – AgroClimas” aims to support private and public sector actors in Colombia, Guatemala and Honduras to implement and use agro-climatic risk management tools, validated and adjusted to the needs of final users. This info note presents results from a mapping of actors and agro-climatic information needs in crops important for food security (maize and bush beans), in pilot sites of the project in Colombia. The hypothesis underlying the study is that through mapping actors who transmit information (climatic, prices, technical and financial) to farmers, knowing if this information is considered reliable, identifying unattended information needs and preferred formats to receive it that would support production decisions, one can devise useful, relevant, reliable, sustainable applicable solutions

Estado del arte de los productos de información climática en Colombia

Este trabajo presenta el inventario del estado del arte de los productos de información climática en Colombia. Se espera que este documento se convierta en una guía, para conocer la oferta de información climática disponible en internet, que es relevante en la toma de decisiones agrícolas, identificando cuáles son sus principales usuarios y cuáles son los mecanismos de flujo de información utilizados. La metodología que orienta este documento se basa en el informe técnico, realizado por CATIE, sobre el estado del arte de los productos de información agroclimática en América Central (CATIE, 2015). Con este enfoque, La información fue colectada a través de búsquedas sistemáticas en el buscador web de Google con palabras clave. Adicionalmente, se realizó la revisión de las páginas Web de organismos como el servicio meteorológico y Ministerios de agricultura y de ambiente, y del sector publico/privado como: gremios, corporaciones y centro de investigación. Los resultados muestran aproximadamente 17 instituciones generando información climática, agroclimática y de seguridad alimentaria para Colombia. La mayoría de publicaciones con información agroclimática de forma periódica proviene de instituciones como IDEAM, CENICAFÉ, CENICAÑA y CIAT-CCAFS vinculadas a los cultivos de interés y difundida por AGRONET, páginas web de cada institución y redes sociales. Se recomienda tener un sistema unificado de consulta (metadato y mapa) sobre información de todas las estaciones meteorológicas activas en el territorio nacional, dada la dificultad para encontrar la información. El ámbito geográfico de las publicaciones abarca en muchos casos la escala nacional, pero se encuentra distintas publicaciones para las principales ciudades, enfoque en departamentos específicos. El tipo de usuarios a los cuales se dirige la información son, en su mayoría para técnicos o servicios de extensión, pero se encuentran algunas publicaciones enfocadas para agricultores a través de boletines en formato físico y medios audiovisuales. Se encontraron varias publicaciones con recomendaciones para apoyar la toma de decisiones en el sector agropecuario, ya sea por cultivos o por región productiva. La periodicidad de las publicaciones varía desde información en tiempo real, corto plazo (días), análisis decadales e información mensual. Se percibe en reuniones con diferentes usuarios de información climática un alto nivel de desconocimiento sobre toda la oferta y utilidad de dicha información para la toma de decisiones en el sector agropecuario

On the Communication Complexity of Secure Computation

Information theoretically secure multi-party computation (MPC) is a central primitive of modern cryptography. However, relatively little is known about the communication complexity of this primitive. In this work, we develop powerful information theoretic tools to prove lower bounds on the communication complexity of MPC. We restrict ourselves to a 3-party setting in order to bring out the power of these tools without introducing too many complications. Our techniques include the use of a data processing inequality for residual information - i.e., the gap between mutual information and G\'acs-K\"orner common information, a new information inequality for 3-party protocols, and the idea of distribution switching by which lower bounds computed under certain worst-case scenarios can be shown to apply for the general case. Using these techniques we obtain tight bounds on communication complexity by MPC protocols for various interesting functions. In particular, we show concrete functions that have "communication-ideal" protocols, which achieve the minimum communication simultaneously on all links in the network. Also, we obtain the first explicit example of a function that incurs a higher communication cost than the input length in the secure computation model of Feige, Kilian and Naor (1994), who had shown that such functions exist. We also show that our communication bounds imply tight lower bounds on the amount of randomness required by MPC protocols for many interesting functions.Comment: 37 page

Efficient, XOR-Based, Ideal (t,n)− threshold Schemes

We propose a new, lightweight (t; n) threshold secret shar- ing scheme that can be implemented using only XOR operations. Our scheme is based on an idea extracted from a patent application by Hewlett Packard that utilises error correction codes. Our scheme im- proves on the patent by requiring fewer randomly generated bits and by reducing the size of shares given to each player, thereby making the scheme ideal. We provide a security proof and e ciency analysis. We compare our scheme to existing schemes in the literature and show that our scheme is more e cient than other schemes, especially when t is large

Información agro-climática local, confiable y oportuna, una necesidad de los agricultores colombianos

Conocer información climática relevante hacia el futuro a través de las predicciones climáticas, no es suficiente para apoyar la toma de decisiones de los agricultores. Es necesario buscar alternativas de manejo agrícola para adaptarse a las condiciones climáticas e implementar mecanismos eficaces y sostenibles, bajo un marco de comunicación efectiva con el agricultor (Jones, 2003; Pulwarty et al., 2003). En América Latina son pocas las iniciativas relacionadas con predicción agroclimática. Por lo anterior, el proyecto “Servicios agroclimáticos e información de seguridad alimentaria para una mejor toma de decisiones – AgroClimas” busca apoyar a los actores del sector privado y público de Colombia, Guatemala y Honduras para implementar y usar herramientas de gestión del riesgo agro-climático, validadas y ajustadas a las necesidades de los usuarios finales. Esta nota presenta los resultados del mapeo de actores y necesidades de información agroclimática en cultivos de seguridad alimentaria (maíz y frijol arbustivo), en sitios piloto del proyecto en Colombia. El trabajo se basa en el supuesto que, mapeando los actores que transmiten información de clima, de precios, financiera y agronómica a los agricultores, conociendo la confianza en la información proporcionada, identificando las necesidades de información y los formatos preferidos para recibir información que apoye la toma de decisiones productivas, se pueden proponer soluciones útiles, relevantes, confiables, sostenibles y aplicables

Combinatorial Bounds and Characterizations of Splitting Authentication Codes

We present several generalizations of results for splitting authentication codes by studying the aspect of multi-fold security. As the two primary results, we prove a combinatorial lower bound on the number of encoding rules and a combinatorial characterization of optimal splitting authentication codes that are multi-fold secure against spoofing attacks. The characterization is based on a new type of combinatorial designs, which we introduce and for which basic necessary conditions are given regarding their existence.Comment: 13 pages; to appear in "Cryptography and Communications