Cyberspace and Time: A Light through the Fog?

International audienceOne usually describes cyberspace as a virtual realm. In truth, it is grounded in real infrastruc-tures, which therefore inherit local regulations and broader geopolitical influences from the location where they are set up. The consequences of this attachment to a place can be measured to some extent from the communications happening in cyberspace, i.e., through communication networks. But there is also a temporal anchorage resulting from phenomena such as synchronisation in communications which, when analysed, reveals deep and surprising proximities, shedding new light on the relationships between actors in cyberspace. We discuss in particular how an analysis of synchronicity in cyberspace helped to identify collusions and a diffusion network active in spreading radical messages, as well as providing insight in these groups' internal structure.Le cyberespace constitue un domaine généralement décrit comme virtuel. Mais il est bâti en réalité sur des infrastructures tout à fait existantes, qui sont dès lors sujettes aux législations territoriales, et aux influences géopolitiques héritées des lieux où elles sont installées. Cet ancrage terrestre laisse des traces, mesurables, dans les échanges qui se tiennent dans le cyberespace, via les réseaux de télécommunication. Mais il y a également un ancrage dans le temps, réalisé par exemple par la synchronicité des échanges, et qui révèle des proximi-tés d'une autre nature, éclairant les relations entre acteurs du cyberespace selon un angle nouveau. En particulier, nous illustrons comment une étude du temps dans le cyberespace a permis d'identifier des collusions à large échelle dans la diffusion de messages à contenu radical, et la structure des groupes de diffusion

Cyberspace and Time: A Light through the Fog?

International audienceOne usually describes cyberspace as a virtual realm. In truth, it is grounded in real infrastruc-tures, which therefore inherit local regulations and broader geopolitical influences from the location where they are set up. The consequences of this attachment to a place can be measured to some extent from the communications happening in cyberspace, i.e., through communication networks. But there is also a temporal anchorage resulting from phenomena such as synchronisation in communications which, when analysed, reveals deep and surprising proximities, shedding new light on the relationships between actors in cyberspace. We discuss in particular how an analysis of synchronicity in cyberspace helped to identify collusions and a diffusion network active in spreading radical messages, as well as providing insight in these groups' internal structure.Le cyberespace constitue un domaine généralement décrit comme virtuel. Mais il est bâti en réalité sur des infrastructures tout à fait existantes, qui sont dès lors sujettes aux législations territoriales, et aux influences géopolitiques héritées des lieux où elles sont installées. Cet ancrage terrestre laisse des traces, mesurables, dans les échanges qui se tiennent dans le cyberespace, via les réseaux de télécommunication. Mais il y a également un ancrage dans le temps, réalisé par exemple par la synchronicité des échanges, et qui révèle des proximi-tés d'une autre nature, éclairant les relations entre acteurs du cyberespace selon un angle nouveau. En particulier, nous illustrons comment une étude du temps dans le cyberespace a permis d'identifier des collusions à large échelle dans la diffusion de messages à contenu radical, et la structure des groupes de diffusion

Quotient Hash Tables - Efficiently Detecting Duplicates in Streaming Data

This article presents the Quotient Hash Table (QHT) a new data structure for duplicate detection in unbounded streams. QHTs stem from a corrected analysis of streaming quotient filters (SQFs), resulting in a 33\% reduction in memory usage for equal performance. We provide a new and thorough analysis of both algorithms, with results of interest to other existing constructions. We also introduce an optimised version of our new data structure dubbed Queued QHT with Duplicates (QQHTD). Finally we discuss the effect of adversarial inputs for hash-based duplicate filters similar to QHT.Comment: Shorter version was accepted at SIGAPP SAC '1

Mixed-radix Naccache-Stern encryption

In this work we explore a combinatorial optimization problem stemming from the Naccache-Stern cryptosystem. We show that solving this problem results in bandwidth improvements, and suggest a polynomial-time approximation algorithm to find an optimal solution. Our work suggests that using optimal radix encoding results in an asymptotic 50% increase in bandwidth

A French cipher from the late 19th century

The Franco-Prussian war (1870--1871) was the first major European conflict during which extensive telegraph use enabled fast communication across large distances. Field officers would therefore have to learn how to use secret codes. But training officers also raises the probability that defectors would reveal these codes to the enemy. Practically all known secret codes at the time could be broken if the enemy knew how they worked. Under Kerckhoffs\u27 impulsion, the French military thus developed new codes, meant to resist even if the adversary knew the encoding and decoding algorithms, but simple enough to be explained and taught to military personnel. Many of these codes were lost to history. One of the designs however, due to Major H. D. Josse, has been recovered and this article describes the features, history, and role of this particular construction. Josse\u27s code was considered for field deployment and underwent some experimental tests in the late 1800s, the result of which were condensed in a short handwritten report. During World War II, German forces got hold of documents describing Josse\u27s work, and brought them to Berlin to be analyzed. A few years later these documents moved to Russia, where they have resided since

Flexible lensless endoscope with a conformationally invariant multi-core fiber

The lensless endoscope represents the ultimate limit in miniaturization of imaging tools: an image can be transmitted through a (multi-mode or multi-core) fiber by numerical or physical inversion of the fiber's pre-measured transmission matrix. However, the transmission matrix changes completely with only minute conformational changes of the fiber, which has so far limited lensless endoscopes to fibers that must be kept static. In this letter we report for the first time a lensless endoscope which is exempt from the requirement of static fiber by designing and employing a custom-designed conformationally invariant fiber. We give experimental and theoretical validations and determine the parameter space over which the invariance is maintained