# LSV Seminar

The LSV seminar takes place on Tuesday at 11:00 AM. The usual location is the conference room at Pavillon des Jardins (venue).
If you wish to be informed by e-mail about upcoming seminars, please contact Stéphane Le Roux and Matthias Fuegger.

The seminar is open to public and does not require any form of registration.

## Past Seminars

### Making Random Choices Invisible to the Scheduler

- Date
- Tuesday, October 30 2007 at 11:00AM
- Place
- Salle de Conférence (Pavillon des Jardins)
- Speaker
- Kostas Chatzikokolakis (LIX, Ecole Polytechnique)

When dealing with process calculi and automata which express both nondeterministic and probabilistic behavior, it is customary to introduce the notion of scheduler to resolve the nondeterminism. It has been observed that for certain applications, notably those in security, the scheduler needs to be restricted so not to reveal the outcome of the protocol's random choices, or otherwise the model of adversary would be too strong even for "obviously correct" protocols. In this talk I present a process-algebraic framework in which the control on the scheduler can be specified in syntactic terms, and I show how to apply it to solve the problem mentioned above. I also consider the definition of (probabilistic) may and must preorders, and show that they are precongruences with respect to the restricted schedulers. Furthermore, I show that all the operators of the language, except replication, distribute over probabilistic summation, which is a useful property for verification. This framework is applied to the dining cryptographers problem, where the scheduler problem comes into play.