Rewrite based Verification of XML Updates

We consider problems of access control for update of XML documents. In the context of XML programming, types can be viewed as hedge automata, and static type checking amounts to verify that a program always converts valid source documents into also valid output documents. Given a set of update operations we are particularly interested by checking safety properties such as preservation of document types along any sequence of updates. We are also interested by the related policy consistency problem, that is detecting whether a sequence of authorized operations can simulate a forbidden one. We reduce these questions to type checking problems, solved by computing variants of hedge automata characterizing the set of ancestors and descendants of the initial document type for the closure of parameterized rewrite rules

Compiling symbolic attacks to protocol implementation tests

Recently efficient model-checking tools have been developed to find flaws in security protocols specifications. These flaws can be interpreted as potential attacks scenarios but the feasability of these scenarios need to be confirmed at the implementation level. However, bridging the gap between an abstract attack scenario derived from a specification and a penetration test on real implementations of a protocol is still an open issue. This work investigates an architecture for automatically generating abstract attacks and converting them to concrete tests on protocol implementations. In particular we aim to improve previously proposed blackbox testing methods in order to discover automatically new attacks and vulnerabilities. As a proof of concept we have experimented our proposed architecture to detect a renegotiation vulnerability on some implementations of SSL/TLS, a protocol widely used for securing electronic transactions.Comment: In Proceedings SCSS 2012, arXiv:1307.802

Detecting Communities under Differential Privacy

Complex networks usually expose community structure with groups of nodes sharing many links with the other nodes in the same group and relatively few with the nodes of the rest. This feature captures valuable information about the organization and even the evolution of the network. Over the last decade, a great number of algorithms for community detection have been proposed to deal with the increasingly complex networks. However, the problem of doing this in a private manner is rarely considered. In this paper, we solve this problem under differential privacy, a prominent privacy concept for releasing private data. We analyze the major challenges behind the problem and propose several schemes to tackle them from two perspectives: input perturbation and algorithm perturbation. We choose Louvain method as the back-end community detection for input perturbation schemes and propose the method LouvainDP which runs Louvain algorithm on a noisy super-graph. For algorithm perturbation, we design ModDivisive using exponential mechanism with the modularity as the score. We have thoroughly evaluated our techniques on real graphs of different sizes and verified their outperformance over the state-of-the-art

Combinable Extensions of Abelian Groups

The design of decision procedures for combinations of theories sharing some arithmetic fragment is a challenging problem in verification. One possible solution is to apply a combination method à la Nelson-Oppen, like the one developed by Ghilardi for unions of non-disjoint theories. We show how to apply this non-disjoint combination method with the theory of abelian groups as shared theory. We consider the completeness and the effectiveness of this non-disjoint combination method. For the completeness, we show that the theory of abelian groups can be embedded into a theory admitting quantifier elimination. For achieving effectiveness, we rely on a superposition calculus modulo abelian groups that is shown complete for theories of practical interest in verification

Towards a Constrained-based Verification of Parameterized Cryptographic Protocols

International audienceAlthough many works have been dedicated to standard protocols like Needham-Schroeder very few address the more challenging class of group protocol s. We present a synchronous model for group protocols, that generalizes standard protocol models by permitting unbounded lists inside messages. In this extended model we propose a correct and complete set of inference rules for checking security properties in presence of an active intruder for the class of well-tagged protocols. Our inference system generalizes the ones that are implemented in several tools for a bounded number of sessions and fixed size lists in message. In particular when applied to protocols whose specification does not contain unbounded lists our inference system provides a decision procedure for secrecy in the case of a fixed number of sessions

Toward an Automatic Analysis of Web Service Security

Web services send and receive messages in XML syntax with some parts hashed, encrypted or signed, according to the WS-Security standard. In this paper we introduce a model to formally describe the protocols that underly these services, their security properties and the rewriting attacks they might be subject to. Unlike with usual security protocols, we have to address here the facts that: (1) The Web service receive/send actions are nondeterministic to accommodate the XML format and the lack of normalization in parsing XML messages. Our model is designed to permit non-deterministic operations. (2) The Web service message format is better modelled with multiset constructors than with fixed arity symbols. Hence we had to introduce an attacker model that handles associativecommutative operators. In particular we present a decision procedure for insecurity of Web services with messages built using encryption, signature, and other cryptographic primitives

A Maximum Variance Approach for Graph Anonymization

Best Paper AwardInternational audienceUncertain graphs, a form of uncertain data, have recently attracted a lot of attention as they can represent inherent uncertainty in collected data. The uncertain graphs pose challenges to conventional data processing techniques and open new research directions. Going in the reserve direction, this paper focuses on the problem of anonymizing a deterministic graph by converting it into an uncertain form. The paper first analyzes drawbacks in a recent uncertainty-based anonymization scheme and then proposes Maximum Variance, a novel approach that provides better tradeoff between privacy and utility. Towards a fair com-parison between the anonymization schemes on graphs, the second con-tribution of this paper is to describe a quantifying framework for graph anonymization by assessing privacy and utility scores of typical schemes in a unified space. The extensive experiments show the effectiveness and efficiency of Maximum Variance on three large real graphs

The Practice of Cryptographic Protocol Verification

AbstractWe present CASRUL, a compiler for cryptographic protocols specifications. Its purpose is to verify the executability of protocols and to translate them into rewrite rules that can be used by several kinds of automatic or semi-automatic tools for finding design flaws. We also present a related complexity results concerning the protocol insecurity problem for a finite number of sessions. We show the problem is in NP without assuming bounds on messages and with non-atomic encryption keys. We also explain that in order to build an attack with a fixed number of sessions the intruder needs only to forge messages of linear size, provided that they are represented as dags.For more information: http://www.loria.fr/equipes/protheo/SOFTWARES/CASRUL/

Enforcing Privacy in Decentralized Mobile Social Networks

International audienceThis position paper first summarizes work done by the first author on location privacy and differential privacy. These techniques will help to solve privacy problems in decentralized mobile social networks, which is the main theme of his PhD research. The paper then briefly reviews the state-of-the-art in privacy-preservation of social graphs and clarifies the lack of attention to graph sharing in decentralized setting. Finally, some initial ideas on how to realize such soft decentralized access controls are described

Orchestration under Security Constraints

International audienceAutomatic composition of web services is a challenging task. Many works have considered simplified automata models that abstract away from the structure of messages exchanged by the services. For the domain of secured services (using e.g. digital signing or timestamping) we propose a novel approach to automated composition of services based on their security policies. Given a community of services and a goal service, we reduce the problem of composing the goal from services in the community to a security problem where an intruder should intercept and redirect messages from the service community and a client service till reaching a satisfying state. We have implemented the algorithm in AVANTSSAR Platform and applied the tool to several case studies