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—CAPTCHAs, which are automated tests intended to distinguish humans from programs, are used on many web sites to prevent bot-based account creation and spam. To avoid imposing undue user friction, CAPTCHAs must be easy for humans and difficult for machines. However, the scientific basis for successful CAPTCHA design is still emerging. This paper examines(More)
We address the question of what kind of asynchronous communication is exactly modeled by the asynchronous π-calculus (πa). To this purpose we define a calculus π B where channels are represented explicitly as special buffer processes. The base language for π B is the (synchronous) π-calculus, except that ordinary processes communicate only via buffers. Then(More)
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt età la diffusion(More)
In this survey paper we consider the class of protocols for information-hiding which use randomization to obfuscate the link between the observables and the information to be protected. We focus on the problem of formalizing the notion of information hiding, and verifying that a given protocol achieves the intended degree of protection. Without the pretense(More)
Generating multimedia streams, such as in a netradio, is a task which is complex and difficult to adapt to every users' needs. We introduce a novel approach in order to achieve it, based on a dedicated high-level functional programming language, called Liquidsoap, for generating, manipulating and broadcasting multimedia streams. Unlike traditional(More)
iii La Nature est un temple o` u de vivants piliers Laissent parfois sortir de confuses paroles ; L'homme y passè a travers des forêts de symboles Qui l'observent avec des regards familiers. Comme de longséchos qui de loin se confondent Dans une ténébreuse et profonde unité, Vaste comme la nuit et comme la clarté, Les parfums, les couleurs et les sons se(More)
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