Jean-Christophe Dubacq

Jean-Christophe Dubacq is maître de conférences at the LIPN.

His topics are mostly:

GPG Key transition statement

I am switching my GPG key from an old 1024 bits DSA key to a new 4096 bits RSA key. The old key will continue to be valid for some time but I prefer all new correspondance to be encrypted with the new key. I will be making all signatures ...

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Hello world!

In programming, that's the way to test a language for the first time.

This site was made with Pelican, with a bunch of plugins, including the i18n_subsite and some of my making. Enjoy!

Distributed Computing by example : Security in Computational Grids

I took part to the writing of one chapter of the book Systèmes répartis en action, edited by Fabrice Kordon, Laurent Pautet and Laure Petrucci. This book, in French, is a survey of current technologies in distributed computing, that is computations using from a few processors up to very large scale computing grids. The goal was to make this survey through the study of several examples, linking real applications to a larger view of the field of distributed computing, including the formal methods and algorithms typical of the domain.

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Performance Analysis of Publish/Subscribe Systems

The Desktop Grid offers solutions to overcome several challenges and to answer increasingly needs of scientific computing. This technology consists mainly in exploiting PC resources, geographically dispersed, to treat time consuming applications and/or important storage capacity requiring applications. However, as resources number increases, the need for scalability, self-organisation, dynamic reconfiguration, decentralization and performance becomes more and more essential. Since such properties are exhibited by P2P systems, the convergence of grid computing and P2P computing seems natural. In this context, this paper evaluates the scalability and performance of P2P tools for registering and discovering services (Publish/Subscribe systems). Three protocols are used in this purpose: Bonjour, Avahi and Pastry. We have studied the behaviour of these protocols related to two criteria: the elapsed time for registrations services and the needed time to discover new services. Our aim is to analyse these results in order to choose the most adequate protocol for creating a decentralized middleware for Desktop Grid.

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Study of the NP-completeness of the Compact Table

The problem of compact tables is to maximise the overlap when building a word that is to include permutations of every given words (all the words being the same length). This problem is shown to be NP-complete in the general case, and some specific restrictions are studied.

To show this on a small example (beyond what is in the article), imagine that in a game (like checkers) if blue takes red, on a result of 1, both are eliminated, on 2 or 3, red remains and blue remains in the other cases. If red takes blue, results 1 to 4 make red win and on 5 to 6, blue wins. The compact table in this case would be to keep the table as is in the blue versus red, add +2 if red versus blue, with results 7 and 8 letting red win.

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