Michaël Rusinowitch (LORIAINRIALorraine)
Program Committee
Important Dates
Contact
For further informations please send
an email to sofronie@mpiinf.mpg.de

List of papers (with abstracts)
09:3010:30 
Michaël Rusinowitch (LORIAINRIALorraine) (invited paper)
Some Decision Problems Related to Cryptographic Protocol Verification
Cryptographic protocols such as IKE, SET, TLS, Kerberos have been developed
to secure electronic transactions. However the design
of such protocols often appears to be problematic even
assuming that the cryptographic primitives are perfect, i.e.
even assuming we cannot decrypt a message without the right key.
An intruder can intercept messages, analyse them, modify
them without needing much computing power and then carry out malevolent actions.
This may lead to a variety of attacks such as wellknown ManintheMiddle attacks.
Many teams in recent years have been working on tools for security protocols automated analysis.
The vast majority of these tools model messages as terms in a suitable term algebra
and makes two assumptions: first that cryptography is
unbreakable (often called the perfect cryptography assumption)
and second that the protocol messages are exchanged over a network that
is under the full control of an active adversary, often called the DolevYao intruder.
Even with these simplifying abstractions, the problem of whether a
protocol actually provides the security properties it has been designed
for is undecidable.
We will present some decidable cases and their complexity
especially for the verification of security properties in more accurate models
that take into account algebraic properties of the cryptographic primitives.
We will also discuss the problem of combining decision procedures for arbitrary intruder
theories with disjoint sets of operators.

11:0011:35 
Stephanie Delaune, Hai Lin and Christopher Lynch (regular paper)
Protocol Verification via Rigid/Fleixble Resolution
In this paper we propose a decision procedure, i.e.,
an inference system for clauses containing rigid and flexible
variables. Rigid variables are only allowed to have one instantiation,
whereas flexible variables are allowed as many instantiations
as desired. We assume a set of clauses containing
only rigid variables together with a set of clauses containing only
flexible variables. When the flexible clauses fall
into a particular class, we
propose an inference system based on ordered
resolution that is sound and complete and for which the
inference procedure will halt.
An interest of this form of problem is for cryptographic protocol
verification for a bounded number of protocol instances.
Our class allows us to obtain a generic decidability result for a large class
of cryptographic protocols that may use for instance CBC encryption
and blind signature.

11:3512:10 
Aharon Abadi, Alexander Rabinovich and Mooly Sagiv
(regular paper)
Decidable Fragments of Many Sorted Logic
We investigate the possibility of developing a decidable logic which
allows expressing a large variety of real world specifications. The
idea is to define a decidable subset of many sorted (typed) first
order logic. The motivation is that types simplify the complexity of
mixed quantifiers when they quantify over different types. We
noticed that many real world verification problems can be formalized
by quantifying over different types in such a way that the relations
between types remain simple.
Our main result is a decidable fragment of many sorted firstorder logic
with limited usage of functions that captures many real world specifications

12:1012:30 
Maria Paola Bonacina and Mnacho Echenim (presentationonly paper)
Decision procedures for variableinactive theories
and two polynomial Tsatisfiability procedures
Verification problems require to reason in theories of data structures
and fragments of arithmetic. Thus, decision procedures for such theories
are needed, to be embedded in, or interfaced with, proof assistants or
software model checkers. Such decision procedures ought to be sound and
complete, to avoid false negatives and false positives, efficient,
to handle large problems, and easy to combine, because problems involve
multiple theories. The rewritebased approach to decision procedures aims
at addressing these sometimes conflicting issues in a uniform way, by
harnessing the power of general firstorder theorem proving. In this
paper, we generalize the rewritebased approach from deciding the
satisfiability of sets of ground literals to deciding that of arbitrary
ground formulae in the theory. Next, we present polynomial rewritebased
satisfiability procedures for the theories of records with extensionality
and integer offsets. Our results use the same key property 
termed variableinactivity  that allows us to combine theories
in a simple way in the rewritebased approach.

14:0014:35 
Linh Anh Nguyen (regular paper)
Approximating Horn Knowledge Bases in Regular
Description Logics to Have PTIME Data Complexity
In description logics, an RBox is a finite set of assertions of the form
$R_{s_1} \circ\ldots\circ R_{s_k} \sqsubseteq R_t$, where
$R_{s_1}$, \ldots, $R_{s_k}$, $R_t$ are role names. A regular
RBox is an RBox whose set of corresponding grammar rules
$t \to s_1 \ldots s_k$ forms a grammar such that, for every symbol
$s$ of the grammar, the set of words derivable from $s$ using the
grammar is a regular language. We assume that a regular RBox is
specified by the corresponding finite automata. By \REG\ we
denote the description logic \ALC\ with regular RBoxes.
A Horn knowledge base in \REG\ is a tuple $(\mR,\mT,\mA)$
consisting of a regular RBox $\mR$, a TBox $\mT$ being a positive
logic program for defining concepts, and an ABox $\mA$ of elementary
facts about individuals and roles. The instance checking problem in such
a Horn knowledge base is to check whether a given individual $a$ is an
instance of a given positive concept $C$ w.r.t. the knowledge base.
The data complexity of this problem (measured when $\mA$ varies)
is coNPhard. We present and study ``good'' approximations of this
problem that have PTIME data complexity. We use a so called deterministic
Horn fragment of \REG\ and give an algorithm for constructing a
``least pseudomodel'' of a Horn knowledge base $(\mR,\mT,\mA)$
in \REG\ for the case $\mT$ is a ``deterministic positive logic program''.

14:3515:10 
Didier Galmiche and Daniel Mery (regular paper)
Connectionbased proof search in intuitionistic logic
from transitive closure of constraints
We present a new constraintbased calculus for intuitionistic
propositional logic (IPL) which gives rise to a new connectionbased
characterization of intuitionistic provability. Compared to other
freevariable tableaux or connectionbased systems, our calculus
replaces socalled prefixes by labels and constraints directly
derived from the relational Kripke semantics for IPL.
In order to characterize intuitionistic provability, the use of
constraints instead of prefixes allows us to drop complex
prefixunification algorithms in favour of a more direct and
simple transitive closure operation on constraints.
We show the soundness and completeness of the system, give
strong arguments for its termination, and explain how it can
be used to build countermodels in case of nonprovability.

15:1015:30 
Carsten Lutz and Frank Wolter (presentationonly paper)
Conservative extensions in modal and description logics
A theory T is a conservative extension of a theory T' if every consequence of
T in the language of T' is a consequence of T' already. Conservative
extensions have been introduced and investigated in mathematical logic
and philosophy of science. More recently, they have been used to
formalise notions of refinement and modularity
in software specification and ontologies. In this talk we discuss the
decidability and computational complexity of the following problem:
is a given finitely axiomatized theory a conservative extension of
another finitely axiomatized theory.
We present results and open problems for modal and description logics.
We also introduce deciding conservative extensions as a challenging new
problem for automated reasoning.

16:0016:20 
Sava Krstic, Amit Goel, Jim Grundy and Cesare Tinelli. (presentationonly paper)
Combined Satisfiability Modulo Parametric Theories
We give a fresh theoretical foundation for designing comprehensive
solvers for satisfiability modulo theories (SMT). In contrast with
the traditional NelsonOppen approach dealing with theories in
single or multisorted firstorder logic, we consider parametric
theoriesa restricted class of theories defined in the context of
a higherorder logic with polymorphic types. Our main result is the
combination theorem for decision procedures for disjoint parametric theories.
Combinations of parametric theories conveniently express the "logic"
of common datatypes, covering virtually all deeply nested structures
(lists of arrays of sets of ...) that arise in verification practice.
The vexatious stable infiniteness condition of the traditional approach
is replaced in our setting with a milder flexibility condition.
Our results do not subsume existing results, nor are subsumed by them,
but they apply more widely because the datatypes relevant in applications
are described by theories that satisfy our parametricity requirements
without necessarily satisfying the stable infiniteness requirements of
other combination methods.

16:2016:40 
Leonardo de Moura, and
Nikolaj Bjorner (presentationonly paper)
Modelbased Theory Combination
Traditional methods for combining theory solvers rely on capabilities of the
solvers to produce all implied equalities or a preprocessing step that
introduces additional literals into the search space.
This paper introduces a combination method that incrementally reconciles
models maintained by each theory. We evaluate the practicality and
efficiency of this approach.

16:4017:00 
Viktor Kuncak, Charles Bouillaguet, Thomas Wies, Karen Zee
and Martin Rinard. (presentationonly paper)
Decision procedures for data structure verification
We describe our experience in using and developing decision
procedures and theorem provers to verify partial correctness
of dynamically allocated data structures such as lists,
queues, trees, and hash tables. We describe a simple and
flexible (even if incomplete) technique for combination of
expressive logics within a software verification system. We
then outline our integration of firstorder theorem provers,
satisfiability modulo theory procedures, monadic
secondorder logic over trees, a decision procedure for
Boolean Algebra with Presburger Arithmetic, and interactive
theorem provers such as Isabelle.
We sketch some results we obtained in this line of research,
including soundness and completeness of omitting disjoint
sorts from firstorder logic with overloaded equality
operator, completeness of verifying preservation of certain
invariants that contain universally quantified "field
constraint" conjuncts, as well as complexity of a logic that
enables reasoning about sizes of unbounded finite sets.
These results suggest that software analysis and
verification can be a great inspiration for research in
decision procedures and automated deduction.

