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Comète-Parsifal Seminar (Abstracts 2007) |
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Abstracts
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Nov 20 2007, 14:00
Speaker:
Simon Kramer
Title: Towards Interactive Belief, Knowledge, and Provability:
Possible Application to Zero-Knowledge Proofs
Abstract:
We argue that modal operators of interactive belief,
knowledge, and provability are definable as natural
generalisations of their non-interactive counterparts,
and that zero-knowledge proofs (from cryptography) have
a natural (modal) formulation in terms of interactive
individual knowledge, non-interactive propositional
knowledge and interactive provability.
Our work is motivated by van Benthem's investigation
into rational agency and dialogue and our attempt to
redefine modern cryptography in terms of modal logic.
Nov 15 2007, 14:00
Speaker:
Antonino Salibra
Title: Algebra and topology in lambda calculus
Abstract:
In this seminar we show how algebra and topology can be fruitfully applied to
the operational semantics and to the model theory of the untyped
lambda calculus. It will be also analyzed one of the long-standing
open problem of lambda calculus, regarding the existence of a topological
model of the beta-eta lambda theory, where all Scott-continuous functions
are representable.
Oct 29 2007, 14:00
Speaker:
Michael Mislove
Title: Probabilistic Input/Output Automata From a Domain-theoretic Perspective
Abstract:
Probabilistic Input/Output Automata (PIOAs) are probabilistic systems that were initially devised by Roberto Segala and have been used as model in a variety of computational settings. Most recently, a variant called Task PIOAs have been used to model crypto-protocols in a way that allows for a finer analysis of lower level mechanisms that underlie modern cryptography. In particular, the approach supports allows the power of the adversary to be restricted while also supporting reasoning about probabilistic polynomial time computations and simulations that are negligible with respect to a meaningful metric. In this talk, I'll describe a domain-theoretic approach to PIOAs that allows a simple derivation of some of the key mathematical results about their structure.
This is joint work with Aaron Jaggard (DIMACS) and Catherine Meadows (NRL).
Oct 16 2007, 14:00
Speaker:
Andrea Turrini
Title: Security Protocol Verification with Probabilistic Automata
Abstract:
We study simulation relations for Probabilistic Automata that
require transitions to be matched up to negligible sets provided
that computation lengths are polynomially bounded. These relations
are meant to provide rigorous grounds to parts of correctness
proofs for cryptographic protocols that are usually carried out by
semi-formal arguments. We illustrate our ideas by recasting a
correctness proof of Bellare and Rogaway based on the notion of
matching conversation.
Paper available here
Oct 11 2007, 14:00
Speaker:
Nicolas Guenot
Title: Multi-Focusing in Deep Inference
Abstract:
The calculus of structures has interesting properties of symmetry,
due to its deep inference feature, which allows to work inside a
formula without destroying the toplevel connectives. In this talk,
we will discuss the problem of defining formally what "focusing"
could be, and how this generic idea can be translated into the
calculus of structures. We will then describe a focused system for
MALL in CoS which naturally comes with the multi-focusing extension,
where several formulas could live under a focusing arrow at the same
time (under the same arrow in the sequent calculus, under several
arrows in CoS). This system is quite simple, has two symmetric
reaction rules unlike Andreoli's system and doesn't need a decision
rule. We will finally present the open topics related to this
system, such as the search for a completeness proof inside the
calculus of structures, which would be more elegant than the
translation from the sequent calculus used so far.
Oct 05 2007, 14:00
Speaker:
Simon Kramer
Title: Animation and Knowledge Programming for the Timed Calculus of Cryptographic Communication
Abstract:
We give an overview of the Timed Calculus of Cryptographic Communication,
one of the very few process calculi for security with real-time capabilities,
and argue that the addition of knowledge programming capabilities to our
calculus is easy. We intend to animate the calculus via logic programming.
URLs: (Thesis, Chapter 4.1 and 4.2)
(LNCS-article)
Oct 02 2007, 14:00
Speaker:
Simon Kramer
Title: The Intended and Actual Meaning of a Cryptographic Message and Protocol
Abstract:
We propose a denotational definition for the (actual) meaning of
a cryptographic message and, based on it, an equational definition
for the context-sensitivity of that meaning, both via hypothetical
knowledge and provability. As a result, we obtain a formalisation of
the first of Abadi and Needham's principles for prudent engineering
practice for --- and a tentative denotational semantics of ---
cryptographic protocols.
Building on this (published) work, we present ongoing work
on the distinction between the intended and the actual meaning of
a cryptographic message and protocol."
URLs: (Thesis, Chapter 4.3)
fcs-arspa07.pdf
(FCS-ARSPA'07 respectively LORI'07)
Jun 19 2007, 14:00
Speaker:
Cosimo Laneve
Title: The must preorder revisited -- an algebraic theory for web services contracts.
Abstract:
We define a language for Web services contracts as a parallel-free fragment of CCS and we study a natural notion of compliance between clients and services in terms of their corresponding contracts. The induced contract preorder turns out to be valuable in searching and querying registries of Web services, it shows interesting connections with the must preorder, and it exhibits good precongruence properties when choreographies of Web
services are considered.
Our contract language may be used as a foundation of Web services
technologies, such as WSDL and WSCL.
HTTP: cs.unibo.it/PiDuce
Jun 12 2007, 14:00
Speaker:
Josef Widder
Title: Consensus in the Presence of Value Faults.
Abstract:
The problem of agreeing on a common value (consensus) encapsulates the
inherent problem of building reliable, i.e., fault tolerant
systems. The faults considered in this talk can be subsumed under
value faults; informally, from the viewpoint of the receiver of some
message, the content of the message may be different from what would
have been received in the absence of faults (i.e., if every component
on the path of the message has worked according to its specification).
The first part of the talk will consider a novel failure model (called
mortal Byzantine) which captures all process failures which eventually
lead to the crash of the faulty process. By considering an optimal
consensus algorithm which tolerates this failure model, we motivate a
more general formalism which should allow to investigate the
requirements of consensus regarding the communication structure in a
distributed computation. In the second part of the talk we will
introduce such a formalism (the heard-of model incorporating value
faults) which allows to separate the requirements on the communication
regarding safety and liveness of consensus while capturing dynamic and
transient link and process failures.
Jun 07 2007, 15:00
Speaker:
Daniele Varacca
Title: Event structure semantics of the pi-calculus.
Abstract:
We propose the first compositional event structure semantics for a fully expressive pi-calculus, generalising Winskel's event structures for CCS. The pi-calculus we model is the pi-calculus with recursive definitions and summations. First we model the synchronous calculus, introducing a notion of dynamic renaming to the standard operators on event structures. Then we model the asynchronous calculus, for which a new additional operator, called rooting, is necessary for representing causality due to new name binding. The semantics are shown to be operationally adequate and sound with respect to bisimulation.
Jun 04 2007, 15:00
Speaker:
Vladimiro Sassone
Title: A Bayesian model for event-based trust.
Abstract:
We focus on systems where trust in a computational entity is
interpreted as the expectation of certain future behaviour based
on behavioural patterns of the past, and concern ourselves with
the foundations of such probabilistic systems. In particular, we
aim at establishing formal probabilistic models for computational
trust and their fundamental properties. In the paper we define a
mathematical measure for quantitatively comparing the effectiveness
of probabilistic computational trust systems in various environments.
With this foundation in place, we formalise a general notion of
information about past behaviour, based on event structures. This
yields a flexible trust model where the probability of complex
protocol outcomes can be assessed.
May 31 2007, 14:00
Speakers:
Kaustuv Chaudhuri and
Joelle Despeyroux
Title: A Hybrid Temporal Logical Framework for Systems Biology.
Abstract:
We propose a logical framework for reasoning in and about systems biology. Our framework is based
on Girard's linear logic, extended with modal situated truth and a temporal interpretation of the
modal worlds. The ``current world'' (or instant of time) can be referred to in the logic using the
localisation operator from hybrid logic, which allows us to describe the delays in a process and
hence the rates of reactions. The resulting logic gives a uniform language for both stochastic
descriptions, such as those based on the Pi-calculus, and continuous ODE descriptions.
May 29 2007, 14:00
Speaker:
Alexandre Miquel
Title: The experimental effectiveness of mathematical proofs.
Abstract:
The Curry-Howard correspondence interprets each mathematical proof
as a program realizing some specification (deduced from the proved
formula). But what happens when the proof relies on experimental
assumptions - for instance laws of physics?
In this talk, I propose to study the frontier between mathematical
reasoning and the empirical hypotheses underlying natural sciences.
For that, I will start from a problem posed by the philosopher Karl
R. Popper on the use of abstract mathematical tools in an empirical
framework. I will then show how modern realizability techniques
can be used to solve this problem, suggesting new ways of combining
mathematical reasoning with experimental protocols effectively.
May 03 2007, 14:30
Speaker:
Robin Milner
Title: An Introduction to Bigraphs.
Abstract:
Bigraphs are a generic model for mobile interactive systems. They have
three aims:
(1) To give a uniform treatment of behavioural equivalences and preorders
in process calculi;
(2) To provide a way to models real-world mobile systems, whether natural
or constructed;
(3) To provide a programming or descriptive tool that will allow real
systems or specifications to be executed, or simulated.
This is the first of three talks on bigraphs in May, and I shall describe
bigraph structure and dynamics slowly, with as much intuition as possible.
I hope I'll get far enough to explain how to exactly recover bisimilarity
for finite CCS in this general framework. This serves (1) above.
The second talk, by Arne Glenstrup on May 10, will serve (2) by explaining
how bigraphs are implemented at ITU Copenhagen.
The third talk, by Jean Krivine on May 22, will serve (3) by modelling
some biology.
May 10 2007, 14:30
Speaker:
Arne Glenstrup
Title: Implementing Matching of Binding Bigraphs.
Abstract:
The Bigraphical Programming Languages (BPL) Project at the IT
University of Copenhagen aims to do research into how programming
languages for mobile and context-aware applications can be based
on the theory of bigraphs.
As a first attempt to operationalise bigraphs, we have implemented
a tool for representing and manipulating binding bigraphs. The
implementation stands out as being closely based on bigraph theory
formally proven correct. It includes representations of normal and
regular forms, as well as algorithms for normalisation and
regularisation.
The keystone that enables simulation of bigraphical reactive systems
is a matching algorithm which is based on an inference system that
has been formally proven sound and complete [1].
This talk will report on major aspects of the ongoing implementation
work.
This is joint work with Lars Birkedal, Troels Christoffer Damgaard
and Espen Hojsgaard.
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[1] Birkedal, L., Damgaard, T. C., Glenstrup, A. J., and Milner, R. (2006b). Matching of bigraphs. In Proceedings of Graph Transformation for Verification and Concurrency Workshop 2006, Electronic Notes in Theoretical Computer Science. Elsevier.
May 22 2007, 14:30
Speaker:
Jean Krivine
Title: A platform for the Simulation and analysis of bio molecular systems in the kappa-calculus.
Abstract:
Joint work with Vincent Danos (Laboratoire Preuves Programmes et Systemes,CNRS, France), Jerome Feret (Ecole Normale Superieure, Paris), Walter Fontana (Systems Biology Department, Harvard Medical School, US).
In this talk we present a tool currently in development at
Plectix Biosystems (Boston, US) allowing to analyse and simulate large
bio molecular systems. The tool relies on an agent based formalism
called kappa [1]. We first present the language in
which states, called solutions or systems, are graphs where
connections are made on sites and transitions are generated by a
restricted class of graph-rewriting rules. We will see that this
language can be neatly represented and extended using bigraph
formalism. We will then proceed with the description of the stochastic
simulation algorithm.
[1] Formal Molecular Biology (TCS 325, 2004) Vincent Danos, Cosimo Laneve
Mar 13 2007, 14:00
Speaker:
Ichiro Hasuo (Joint-work with Yoshinobu Kawabe at NTT Corporation, Japan)
Title: Probabilistic Anonymity via Coalgebraic Simulations.
Abstract:
There is a growing concern on anonymity and privacy
on the Internet, resulting in lots of work on formalization and
verification of anonymity. Especially, importance of probabilistic
aspect of anonymity is claimed recently by many authors. Among them
are Bhargava and Palamidessi who present the definition of
probabilistic anonymity for which, however, proof methods are not yet
elaborated. In this paper we introduce a simulation-based proof method
for probabilistic anonymity. It is a probabilistic adaptation of the
method by Kawabe et al. for nondeterministic anonymity: anonymity of a
protocol is proved by finding out a forward/backward simulation
between certain automata. For the jump from non-determinism to
probability we fully exploit a generic, coalgebraic theory of traces
and simulations developed by Hasuo, Jacobs and Sokolova. In particular, an
appropriate notion of probabilistic simulations is obtained by
instantiating a generic definition with suitable parameters.
REFERENCE:
Ichiro Hasuo and Yoshinobu Kawabe.
Probabilistic Anonymity via Coalgebraic Simulations.
To appear in Proc. ESOP 2007.
Feb 14 2007, 15:00
Speaker:
Daniele Gorla
Title: On the Relative Expressive Power of Calculi for Mobility.
Abstract:
In this talk, we shall comparatively analyse some mainstream
calculi for mobility: the pi-calculus, the distributed pi-calculus,
a distributed version of Linda and Mobile/Boxed/Safe ambients.
In particular, we shall focus on their relative expressive power,
i.e. we shall try to encode one in the other while respecting
some reasonable properties. By means of 'good' encodings, or
impossibility of such results, we set up a hierarchy of these
languages. Finally, we discuss and compare several variants
of ambient-like languages, including objective moves, passwords
and different semantics for the mobility primitives and for parent-child
communications.
Page maintainer:
Carlos Olarte
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