Random Generation and Enumeration of Accessible Determinisitic Real-time Pushdown Automata

This papers presents a general framework for the uniform random generation of deterministic real-time accessible pushdown automata. A polynomial time algorithm to randomly generate a pushdown automaton having a fixed stack operations total size is proposed. The influence of the accepting condition (empty stack, final state) on the reachability of the generated automata is investigated.Comment: Frank Drewes. CIAA 2015, Aug 2015, Umea, Sweden. Springer, 9223, pp.12, 2015, Implementation and Application of Automata - 20th International Conferenc

A Note on Partially Ordered Tree Automata

International audienceA recent paper by Bouajjani, Muscholl and Touili shows that the class of languages accepted by partially ordered word automata (or equivalently accepted by Sigma2-formulae) is closed under semi-commutation and it suggested the following open question: can we extend this result to tree languages? This problem can be addressed by proving 1) that the class of tree regular languages accepted by Sigma2 formulae is strictly included in the class of languages accepted by partially ordered automata, and 2) that Bouajjani and the others results can't be extended to tree

Transitive Closures of Semi-commutation Relations on Regular omega-Languages

A semi-commutation $R$ is a relation on a finite alphabet $A$. Given an infinite word $u$ on $A$, we denote by $R(u)=\{xbay\mid x\in A^*,y\in A^\omega \ (a,b)\in R \text{ and } xaby=u\}$ and by $R^*(u)$ the language $\{u\}\cup \cup_{k\geq 1} R^k(u)$. In this paper we prove that if an $\omega$-language $L$ is a finite union of languages of the form $A_0^*a_1A_1^*\ldots a_k A_k^*a_{k+1}A_{k+1}^*$, where the $A_i$'s are subsets of the alphabet and the $a_i$'s are letters, then $R^*(L)$ is a computable regular $\omega$-language accepting a similar decomposition. In addition we prove the same result holds for $\omega$-languages which are finite unions of languages of the form $L_0a_1L_1\ldots a_k L_ka_{k+1}L_{k+1}$, where the $L_i$'s are accepted by diamond automata and the $a_i$'s are letters. These results improve recent works by Bouajjani, Muscholl and Touili on one hand, and by Cécé, Héam and Mainier on the other hand, by extending them to infinite words

Efficiency of Automata in Semi-Commutation Verification Techniques

Computing the image of a regular language by the transitive closure of a relation is a central question in Regular Model Checking. In a recent paper Bouajjani, Muscholl and Touili proved that the class of APC regular languages is closed under all semi-commutation relations R. Moreover a recursive algorithm on the regular expression is given to compute the image of an APC language by the transitive closure of R. This paper provides a new approach, based on automata, of the same question. Our approach produces a simpler and more efficient algorithm which furthermore works for a larger class of regular languages closed under union, intersection, semi-commutation relations and conjugacy. The existence of this new class, PolC, answered the open question proposed in Bouajjani and al.'s paper

On the Uniform Random Generation of Determinisitic Partially Ordered Automata using Monte Carlo Techniques

Partially ordered automata are finite automata admitting no simple loops of length greater than or equal to 2. In this paper we show how to randomly and uniformly generate deterministic accessible partially ordered automata using Monte-Carlo techniques

Tree Automata for Detecting Attacks on Protocols with Algebraic Cryptographic Primitives

International audienceThis paper extends a rewriting approximations-based theoretical framework in which the security problem -- secrecy preservation against an active intruder -- may be semi-decided through a reachability analysis. In a recent paper, we have shown how to semi-decide whether a security protocol using algebraic properties of cryptographic primitives is safe. In this paper, we investigate the dual - insecurity - problem: we explain how to semi-decide whether a protocol using cryptographic primitive algebraic properties is unsafe. This improvement offers us to draw automatically a complete diagnostic of a security protocol with an unbounded number of sessions. Furthermore, our approach is supported by the tool TA4SP successfully applied for analysing the NSPK-xor protocol and the Diffie-Hellman protocol

From Linear Temporal Logic Properties to Rewrite Propositions

International audienceIn the regular model-checking framework, reachability analysis can be guided by temporal logic properties, for instance to achieve the counter example guided abstraction refinement (CEGAR) objectives. A way to perform this analysis is to translate a temporal logic formula expressed on maximal rewriting words into a "rewrite proposition" - a propositional formula whose atoms are language comparisons, and then to generate semi-decision procedures based on (approximations of) the rewrite proposition. This approach has recently been studied using a non-automatic translation method. The extent to which such a translation can be systematised needs to be investigated, as well as the applicability of approximated methods wherever no exact translation can be effected. This paper presents contributions to that effect: (1) we investigate suitable semantics for LTL on maximal rewriting words and their influence on the feasibility of a translation, and (2) we propose a general scheme providing exact results on a fragment of LTL corresponding mainly to safety formulæ, and approximations on a larger fragment

Automatic Abstraction Generation : How to Make an Expert Verification Technique for Security Protocols available to Non-expert Users

The security problem for protocols with an unbounded number of sessios is in general undecidable. However, a solution may consist of performing reachability analysis on safety-preserving abstractions of security protocols. In order to make this technique available for high level specification languages like HLPSL and PROUVE, we define safe and sound abstractions of protocol transition systems into rewriting systems. These abstractions allow the automated generation of approximation functions to ensure soundness of the reachability analysis. As our main purpose is to automate in so far as possible the analysis of protocols for an unbounded number of sessions, our abstraction/approximation based approach provides an efficient verification tool, TA4SP. This way, the requirement of an expert user can be removed from the verification chain

Computing Semicommutation Closures: a Machine Learning Approach

Semicommutation relations are simple rewriting relation on finite words using rules of the form ab → ba. In this paper we present how to use Angluin style machine learning algorithms to compute the image of regular language by the transitive closure of a semicommutation relation

Handling Algebraic Properties in Automatic Analysis of Security Protocols

This paper extends the approximation-based theoretical framework in which the security problem secrecy preservation against an intruder may be semi-decided through a reachability verification. We explain how to cope with algebraic properties for an automatic approximation-based analysis of security protocols. We prove that if the initial knowledge of the intruder is a regular tree language, then the security problem may by semi-decided for protocols using cryptographic primitives with algebraic properties. More precisely, an automatically generated approximation function enables us 1) an automatic normalization of transitions, and 2) an automatic completion procedure. The main advantage of our approach is that the approximation function makes it possible to verify security protocols with an arbitrary number of sessions. The concepts are illustrated on an example of the view-only protocol using a cryptographic primitive with the exclusive or algebraic property