How to Share and Own a Secret

Custodian service is a service safeguarding a firm\u27s or individual\u27s financial assets or secret information. Such services often present a user with security versus ownership dilemma. The user does not wish to pass full control over their asset to the custodian to facilitate safeguarding. A control sharing mechanism allowing the custodian to hold enough information and keeping the user as the owner of the asset is required. For the assets being secret information, cryptographic protocols addressing this dilemma are known as prepositioned secret sharing~(PSS) protocols. PSS schemes distinguish redundant ``common\u27\u27 shares and specific ``activating\u27\u27 shares controlling the very possibility of the secret information reconstruction. Usually, PSS schemes: 1) lack robustness with respect to the amount of ``common\u27\u27 shares, i.e., a high redundancy degree in ``common\u27\u27 enables them to reconstruct the secret without ``activation\u27\u27, and 2) are inflexible in configuring the robustness of the ``activating\u27\u27 shares, i.e., how many ``activating\u27\u27 shares can be lost or stolen before the secret can be reconstructed. In this paper, we present a PSS addressing these shortcomings

Moving Objects Tracking in Distributed Maritime Observation Systems

This paper considers the processes of target tracking complicated by big data gaps in complex media such as Distributed Maritime Observation System (DMOS). The main purpose of DMOS is to support the favorable navigation conditions, monitoring, life-saving on the sea for different ships in harbors, maritime roads and open sea. DMOS can be considered as a heterogeneous distributed computer system, it includes different layers of services at different levels of abstraction: ship, harbor; regional and global levels. Such a framework is based on several satellite and maritime information systems that nowadays favor the integration of maritime data (e.g., AIS, ECDIS, OPTIMARE, GMDSS). Despite of the input data big volume the situations exist when gaps (e.g., time delays from minutes to hours) between target observations’ points are different. Well known algorithms of target tracking do not work properly in such situations. The proposed approach describes synthesis of analytical and simulation methods at tactical hypothesis development for the cases when suitable direct analytics is not applicable. Also, a joined artificial techniques’ scenario approach to tactical situation hypothesis development is proposed

La marche céleste: une marche oublieuse dans les subdivisions convexes à terminaison garantie

We present a new oblivious walking strategy for convex subdivisions. Our walk isfaster than the straight walk and more generally applicable than the visiblity walk. To provetermination of our walk we use a novel monotonically decreasing distance measure.Nous présentons une nouvelle stratégie de marche pour les subdivisions convexes.Cette stratégie est oublieuse, c’est à dire que la prochaine cellule visitée ne dépends pas des cellulesvisitées précédemment. Notre marche est plus rapide que la marche rectiligne et s’applique à dessubdivisions plus générales que la marche par visibilité. La démonstration de terminaison reposesur la décroissance monotone d’une nouvelle distance mesurant le progrès de la march

Celestial Walk: A Terminating, Memoryless Walk for Convex Subdivisions

International audienceA common solution for routing messages or performing point location in planar subdivisions consists in walking from one face to another using neighboring relationships. If the next face does not depend on the previously visited faces, the walk is called memoryless. We present a new memoryless strategy for convex subdivisions. The known alternatives are straight walk, which is a bit slower and not memoryless, and visibility walk, which is guaranteed to work properly only for Delaunay triangulations. We prove termination of our walk using a novel distance measure that, for our proposed walking strategy, is strictly monotonically decreasing

Low-temperature dynamics of the Curie-Weiss Model: Periodic orbits, multiple histories, and loss of Gibbsianness

We consider the Curie-Weiss model at a given initial temperature in vanishing external field evolving under a Glauber spin-flip dynamics corresponding to a possibly different temperature. We study the limiting conditional probabilities and their continuity properties and discuss their set of points of discontinuity (bad points). We provide a complete analysis of the transition between Gibbsian and non-Gibbsian behavior as a function of time, extending earlier work for the case of independent spin-flip dynamics. For initial temperature bigger than one we prove that the time-evolved measure stays Gibbs forever, for any (possibly low) temperature of the dynamics. In the regime of heating to low-temperatures from even lower temperatures, when the initial temperature is smaller than the temperature of the dynamics, and smaller than 1, we prove that the time-evolved measure is Gibbs initially and becomes non-Gibbs after a sharp transition time. We find this regime is further divided into a region where only symmetric bad configurations exist, and a region where this symmetry is broken. In the regime of further cooling from low-temperatures there is always symmetry-breaking in the set of bad configurations. These bad configurations are created by a new mechanism which is related to the occurrence of periodic orbits for the vector field which describes the dynamics of Euler-Lagrange equations for the path large deviation functional for the order parameter. To our knowledge this is the first example of the rigorous study of non-Gibbsian phenomena related to cooling, albeit in a mean-field setup.Comment: 31 pages, 24 figure