59,776 research outputs found
Endogenous Versus Exogenous Shocks in Complex Networks: an Empirical Test Using Book Sale Ranking
Are large biological extinctions such as the Cretaceous/Tertiary KT boundary
due to a meteorite, extreme volcanic activity or self-organized critical
extinction cascades? Are commercial successes due to a progressive reputation
cascade or the result of a well orchestrated advertisement? Determining the
chain of causality for extreme events in complex systems requires disentangling
interwoven exogenous and endogenous contributions with either no clear or too
many signatures. Here, we study the precursory and recovery signatures
accompanying shocks, that we test on a unique database of the Amazon sales
ranking of books. We find clear distinguishing signatures classifying two types
of sales peaks. Exogenous peaks occur abruptly and are followed by a power law
relaxation, while endogenous sale peaks occur after a progressively
accelerating power law growth followed by an approximately symmetrical power
law relaxation which is slower than for exogenous peaks. These results are
rationalized quantitatively by a simple model of epidemic propagation of
interactions with long memory within a network of acquaintances. The slow
relaxation of sales implies that the sales dynamics is dominated by cascades
rather than by the direct effects of news or advertisements, indicating that
the social network is close to critical.Comment: 5 pages including 3 figures final version published in Physical
Review Letter
A Generic Construction of an Anonymous Reputation System and Instantiations from Lattices
With an anonymous reputation system one can realize the process of rating sellers anonymously in an online shop. While raters can stay anonymous, sellers still have the guarantee that they can be only be reviewed by raters who bought their product.We present the first generic construction of a reputation system from basic building blocks, namely digital signatures, encryption schemes, non-interactive zero-knowledge proofs, and linking indistinguishable tags. We then show the security of the reputation system in a strong security model. Among others, we instantiate the generic construction with building blocks based on lattice problems, leading to the first module lattice-based reputation system
Anonymous reputation based reservations in e-commerce (AMNESIC)
Online reservation systems have grown over the last recent
years to facilitate the purchase of goods and services. Generally,
reservation systems require that customers provide
some personal data to make a reservation effective. With
this data, service providers can check the consumer history
and decide if the user is trustable enough to get the reserve.
Although the reputation of a user is a good metric to implement
the access control of the system, providing personal
and sensitive data to the system presents high privacy risks,
since the interests of a user are totally known and tracked
by an external entity. In this paper we design an anonymous
reservation protocol that uses reputations to profile
the users and control their access to the offered services, but
at the same time it preserves their privacy not only from the
seller but the service provider
A Secure Cooperative Sensing Protocol for Cognitive Radio Networks
Cognitive radio networks sense spectrum occupancy
and manage themselves to operate in unused bands without disturbing licensed users. Spectrum sensing is more accurate if jointly performed by several reliable nodes. Even though cooperative sensing is an active area of research, the secure
authentication of local sensing reports remains unsolved, thus empowering false results. This paper presents a distributed protocol based on digital signatures and hash functions, and an
analysis of its security features. The system allows determining a final sensing decision from multiple sources in a quick and secure way.Las redes de radio cognitiva detectora de espectro se las arreglan para operar en las nuevas bandas sin molestar a los usuarios con licencia. La detección de espectro es más precisa
si el conjunto está realizado por varios nodos fiables. Aunque la detección cooperativa es un área activa de investigación, la autenticación segura de informes locales de detección no ha sido resuelta, por lo tanto se pueden dar resultados falsos. Este trabajo presenta un protocolo distribuido basado en firmas digitales y en funciones hash, y un análisis de sus características de seguridad. El sistema permite determinar una decisión final de detección de múltiples fuentes de una manera rápida y segura.Les xarxes de ràdio cognitiva detectora d'espectre se les arreglen per operar en les noves bandes sense destorbar els usuaris amb llicència. La detecció d'espectre és més precisa
si el conjunt està realitzat per diversos nodes fiables. Encara que la detecció cooperativa és una àrea activa d'investigació, l'autenticació segura d'informes locals de detecció no ha estat resolta, per tant es poden donar resultats falsos. Aquest treball presenta un protocol distribuït basat en signatures digitals i en funcions hash, i una anàlisi de les seves característiques de seguretat. El sistema permet determinar una decisió final de detecció de múltiples fonts d'una manera ràpida i segura
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