arXiv subjects

Étienne André

Publications and source records attributed to Étienne André.

At least 55 records · Page 3Linked to original sources

arXiv2019

Parametric Timed Model Checking for Guaranteeing Timed Opacity

Information leakage can have dramatic consequences on systems security. Among harmful information leaks, the timing information leakage is the ability for an attacker to deduce internal information depending on the system execution time. We address the following problem: given a timed system, synthesize the execution times for which one cannot deduce whether the system performed some secret behavior. We solve this problem in the setting of timed automata (TAs). We first provide a general solution, and then extend the problem to parametric TAs, by synthesizing internal timings making the TA secure. We study decidability, devise algorithms, and show that our method can also apply to program analysis.

cs.CR↗

arXiv2019

On the expressive power of invariants in parametric timed automata

The verification of systems combining hard timing constraints with concurrency is challenging. This challenge becomes even harder when some timing constants are missing or unknown. Parametric timed formalisms, such as parametric timed automata (PTAs), tackle the synthesis of such timing constants (seen as parameters) for which a property holds. Such formalisms are highly expressive, but also undecidable, and few decidable subclasses were proposed. We propose here a syntactic restriction on PTAs consisting in removing guards (constraints on transitions) to keep only invariants (constraints on locations). While this restriction preserves the expressiveness of PTAs (and therefore their undecidability), an additional restriction on the type of constraints allows to not only prove decidability, but also to perform the exact synthesis of parameter valuations satisfying reachability. This formalism, that seems trivial at first sight as it benefits from the decidability of the reachability problem with a better complexity than Timed Automata (TAs), suffers from the undecidability of the whole TCTL logic that TAs, on the contrary enjoy. We believe our formalism allows for an interesting trade-off between decidability and practical expressiveness and is therefore promising. We show its applicability in a small case study.

cs.FL↗

arXiv2019

Time4sys2imi: A tool to formalize real-time system models under uncertainty

Time4sys is a formalism developed by Thales, realizing a graphical specification for real-time systems. However, this formalism does not allow to perform formal analyses for real-time systems. So a translation of this tool to a formalism equipped with a formal semantics is needed. We present here Time4sys2imi, a tool translating Time4sys models into parametric timed automata in the input language of IMITATOR. This translation allows not only to check the schedulability of real-time systems, but also to infer some timing constraints (e.g., deadlines, offsets) guaranteeing schedulability. We successfully applied Time4sys2imi to various examples.

cs.SE↗

arXiv2019

What's decidable about parametric timed automata?

Parametric timed automata (PTAs) are a powerful formalism to reason, simulate and formally verify critical real-time systems. After 25 years of research on PTAs, it is now well-understood that any non-trivial problem studied is undecidable for general PTAs. We provide here a survey of decision and computation problems for PTAs. On the one hand, bounding time, bounding the number of parameters or the domain of the parameters does not (in general) lead to any decidability. On the other hand, restricting the number of clocks, the use of clocks (compared or not with the parameters), and the use of parameters (e.g. used only as upper or lower bounds) leads to decidability of some problems. We also put emphasis on open problems. We also discuss formalisms close to parametric timed automata (such as parametric hybrid automata or parametric interrupt timed automata), and we study tools dedicated to PTAs and their extensions.

cs.LO↗

arXiv2019

Parametric Verification: An Introduction

This paper constitutes a short introduction to parametric verification of concurrent systems. It originates from two 1-day tutorial sessions held at the Petri nets conferences in Toruń (2016) and Zaragoza (2017). The paper presents not only the basic formal concepts tackled in the video version, but also an extensive literature to provide the reader with further references covering the area. We first introduce motivation behind parametric verification in general, and then focus on different models and approaches, for verifying several kinds of systems. They include Parametric Timed Automata, for modelling real-time systems, where the timing constraints are not necessarily known a priori. Similarly, Parametric Interval Markov Chains allow for modelling systems where probabilities of events occurrences are intervals with parametric bounds. Parametric Petri Nets allow for compact representation of systems, and cope with different types of parameters. Finally, Action Synthesis aims at enabling or disabling actions in a concurrent system to guarantee some of its properties. Some tools implementing these approaches were used during hands-on sessions at the tutorial. The corresponding practicals are freely available on the Web.

cs.LO↗

arXiv2019

Repairing Timed Automata Clock Guards through Abstraction and Testing

Timed automata (TAs) are a widely used formalism to specify systems having temporal requirements. However, exactly specifying the system may be difficult, as the user may not know the exact clock constraints triggering state transitions. In this work, we assume the user already specified a TA, and (s)he wants to validate it against an oracle that can be queried for acceptance. Under the assumption that the user only wrote wrong guard transitions (i.e., the structure of the TA is correct), the search space for the correct TA can be represented by a Parametric Timed Automaton (PTA), i.e., a TA in which some constants are parametrized. The paper presents a process that i) abstracts the initial (faulty) TA tainit in a PTA pta; ii) generates some test data (i.e., timed traces) from pta; iii) assesses the correct evaluation of the traces with the oracle; iv) uses the IMITATOR tool for synthesizing some constraints phi on the parameters of pta; v) instantiate from phi a TA tarep as final repaired model. Experiments show that the approach is successfully able to partially repair the initial design of the user.

cs.LO↗

arXiv2019

Consistency in Parametric Interval Probabilistic Timed Automata

We propose a new abstract formalism for probabilistic timed systems, Parametric Interval Probabilistic Timed Automata, based on an extension of Parametric Timed Automata and Interval Markov Chains. In this context, we consider the consistency problem that amounts to deciding whether a given specification admits at least one implementation. In the context of Interval Probabilistic Timed Automata (with no timing parameters), we show that this problem is decidable and propose a constructive algorithm for its resolution. We show that the existence of timing parameter valuations ensuring consistency is undecidable in the general context, but still exhibit a syntactic condition on parameters to ensure decidability. We also propose procedures that resolve both the consistency and the consistent reachability problems when the parametric probabilistic zone graph is finite.

cs.FL↗

arXiv2019

Formalizing Time4sys using parametric timed automata

Critical real-time systems must be verified to avoid the risk of dramatic consequences in case of failure. Thales developed an open formalism Time4sys to model real-time systems, with expressive features such as periodic or sporadic tasks, task dependencies, distributed systems, etc. However, Time4sys does not natively allow for a formal reasoning. In this work, we present a translation from Time4sys to (parametric) timed automata, so as to allow for a formal verification.

cs.SE↗

arXiv2019

Symbolic Monitoring against Specifications Parametric in Time and Data

Monitoring consists in deciding whether a log meets a given specification. In this work, we propose an automata-based formalism to monitor logs in the form of actions associated with time stamps and arbitrarily data values over infinite domains. Our formalism uses both timing parameters and data parameters, and is able to output answers symbolic in these parameters and in the log segments where the property is satisfied or violated. We implemented our approach in an ad-hoc prototype SyMon, and experiments show that its high expressive power still allows for efficient online monitoring.

cs.FL↗

arXiv2019

Parametric analyses of attack-fault trees

Risk assessment of cyber-physical systems, such as power plants, connected devices and IT-infrastructures has always been challenging: safety (i.e. absence of unintentional failures) and security (i.e. no disruptions due to attackers) are conditions that must be guaranteed. One of the traditional tools used to help considering these problems is attack trees, a tree-based formalism inspired by fault trees, a well-known formalism used in safety engineering. In this paper we define and implement the translation of attack-fault trees (AFTs) to a new extension of timed automata, called parametric weighted timed automata. This allows us to parametrize constants such as time and discrete costs in an AFT and then, using the model-checker IMITATOR, to compute the set of parameter values such that a successful attack is possible. Using the different sets of parameter values computed, different attack and fault scenarios can be deduced depending on the budget, time or computation power of the attacker, providing helpful data to select the most efficient counter-measure.

cs.CR↗

arXiv2019

Parametric Timed Broadcast Protocols

In this paper we consider state reachability in networks composed of many identical processes running a parametric timed broadcast protocol (PTBP). PTBP are a new model extending both broadcast protocols and parametric timed automata. This work is, up to our knowledge, the first to consider the combination of both a parametric network size and timing parameters in clock guard constraints. Since the communication topology is of utmost importance in broadcast protocols, we investigate reachability problems in both clique semantics where every message reaches every processes, and in reconfigurable semantics where the set of receivers is chosen non-deterministically. In addition, we investigate the decidability status depending on whether the timing parameters in guards appear only as upper bounds in guards, as lower bounds or when the set of parameters is partitioned in lower-bound and upper-bound parameters.

cs.LO↗

arXiv2019

Parametric schedulability analysis of a launcher flight control system under reactivity constraints

The next generation of space systems will have to achieve more and more complex missions. In order to master the development cost and duration of such systems, an alternative to a manual design is to automatically synthesize the main parameters of the system. In this paper, we present an approach on the specific case of the scheduling of the flight control of a space launcher. The approach requires two successive steps: (1) the formalization of the problem to be solved in a parametric formal model and (2) the synthesis of the model parameters with a tool. We first describe the problematic of the scheduling of a launcher flight control, then we show how this problematic can be formalized with parametric stopwatch automata; we then present the results computed by IMITATOR. We compare the results to the ones obtained by other tools classically used in scheduling.

cs.SE↗

arXiv2018

Verification of an industrial asynchronous leader election algorithm using abstractions and parametric model checking

The election of a leader in a network is a challenging task, especially when the processes are asynchronous, i.e., execute an algorithm with time-varying periods. Thales developed an industrial election algorithm with an arbitrary number of processes, that can possibly fail. In this work, we prove the correctness of a variant of this industrial algorithm. We use a method combining abstraction, the SafeProver solver, and a parametric timed model-checker. This allows us to prove the correctness of the algorithm for a large number p of processes (p=5000).

cs.LO↗

arXiv2018

The language preservation problem is undecidable for parametric event-recording automata

Parametric timed automata (PTA) extend timed automata with unknown constants ("parameters"), at the price of undecidability of most interesting problems. The (untimed) language preservation problem ("given a parameter valuation, can we find at least one other valuation with the same untimed language?") is undecidable for PTAs. We prove that this problem remains undecidable for parametric event-recording automata (PERAs), a subclass of PTAs that considerably restrains the way the language can be used; we also show it remains undecidable even for slightly different definitions of the language, i.e., finite sequences of actions ending in or passing infinitely often through accepting locations, or just all finite untimed words (without accepting locations).

cs.FL↗

arXiv2018

Offline timed pattern matching under uncertainty

Given a log and a specification, timed pattern matching aims at exhibiting for which start and end dates a specification holds on that log. For example, "a given action is always followed by another action before a given deadline". This problem has strong connections with monitoring real-time systems. We address here timed pattern matching in presence of an uncertain specification, i.e., that may contain timing parameters (e.g., the deadline can be uncertain or unknown). That is, we want to know for which start and end dates, and for what values of the deadline, this property holds. Or what is the minimum or maximum deadline (together with the corresponding start and end dates) for which this property holds. We propose here a framework for timed pattern matching based on parametric timed model checking. In contrast to most parametric timed problems, the solution is effectively computable, and we perform experiments using IMITATOR to show the applicability of our approach.

eess.SY↗

arXiv2018

A benchmark library for parametric timed model checking

Verification of real-time systems involving hard timing constraints and concurrency is of utmost importance. Parametric timed model checking allows for formal verification in the presence of unknown timing constants or uncertainty (e.g. imprecision for periods). With the recent development of several techniques and tools to improve the efficiency of parametric timed model checking, there is a growing need for proper benchmarks to test and compare fairly these tools. We present here a benchmark library for parametric timed model checking made of benchmarks accumulated over the years. Our benchmarks include academic benchmarks, industrial case studies and examples unsolvable using existing techniques.

cs.LO↗

arXiv2014

Translating UML State Machines to Coloured Petri Nets Using Acceleo: A Report

UML state machines are widely used to specify dynamic systems behaviours. However its semantics is described informally, thus preventing the application of model checking techniques that could guarantee the system safety. In a former work, we proposed a formalisation of non-concurrent UML state machines using coloured Petri nets, so as to allow for formal verification. In this paper, we report our experience to implement this translation in an automated manner using the model-to-text transformation tool Acceleo. Whereas Acceleo provides interesting features that facilitated our translation process, it also suffers from limitations uneasy to overcome.

cs.SE↗

arXiv2014

Proceedings 1st International Workshop on Synthesis of Continuous Parameters

This volume contains the proceedings of the 1st International Workshop on Synthesis of Continuous Parameters (SynCoP'14). The workshop was held in Grenoble, France on April 6th, 2014, as a satellite event of the 17th European Joint Conferences on Theory and Practice of Software (ETAPS'14). SynCoP aims at bringing together researchers working on parameter synthesis for systems with continuous variables, where the parameters consist of a (usually dense) set of constant values. Synthesis problems for such parameters arise for real-time, hybrid or probabilistic systems in a large variety application domains. A parameter could be, e.g., a delay in a real-time system, or a reaction rate in a biological cell model. The objective of the synthesis problem is to identify suitable parameters to achieve desired behavior, or to verify the behavior for a given range of parameter values. This volume contains seven contributions: two invited talks and five regular papers.

cs.SC↗