International audience

Ensuring the compliance of developed software with general and application-specific security requirements is a challenging task due to the lack of automatic and formal means to lead this verification. In this paper, we present our approach that aims at integrating the formal specification and verification of security guidelines in early stages of the development lifecycle by combining the model checking together with information flow analysis. We present our framework that is based on an extension of LTS (Labeled Transition Systems) by data dependence information to cover the end-to-end specification and verification of security guidelines.

Secure software can be obtained out of two distinct processes: security by design, and security by certification. The former approach has been quite extensively formalized as it builds upon models, which are verified to ensure security properties are attained and from which software is then derived manually or automatically. In contrast, the latter approach has always been quite informal in both specifying security best practices and verifying that the code produced conforms to them. In this paper, we focus on the latter approach and describe how security guidelines might be captured by security experts and verified formally by developers. Our technique relies on abstracting actions in a program based on modularity, and on combining model checking together with information flow analysis. Our goal is to formalize the existing body of knowledge in security best practices using formulas in the MCL language and to conduct formal verifications of the conformance of programs with such security guidelines. We also discuss our first results in creating a methodology for the formalization of security guidelines.

Security flaws are open doors to attack embedded systems and must be carefully assessed in order to determine threats to safety and security. Subsequently securing a system, that is, integrating security mechanisms into the system's architecture can itself impact the system's safety, for instance deadlines could be missed due to an increase in computations and communications latencies. SysML-Sec addresses these issues with a model-driven approach that promotes the collaboration between system designers and security experts at all design and development stages, e.g., requirements, attacks, partitioning, design, and validation. A central point of SysML-Sec is its partitioning stage during which safety-related and security-related functions are explored jointly and iteratively with regards to requirements and attacks. Once partitioned, the system is designed in terms of system's functions and security mechanisms, and formally verified from both the safety and the security perspectives. Our paper illustrates the whole methodology with the evaluation of a security mechanism added to an existing automotive system.

User connectivity patterns in network applications are known to be heterogeneous and to follow periodic (daily and weekly) patterns. In many cases, the regularity and the correlation of those patterns is problematic: For network applications, many connected users create peaks of demand; in contrast, in peer-to-peer scenarios, having few users online results in a scarcity of available resources. On the other hand, since connectivity patterns exhibit a periodic behavior, they are to some extent predictable. This paper shows how this can be exploited to anticipate future user connectivity and to have applications proactively responding to it. We evaluate the probability that any given user will be online at any given time, and assess the prediction on 6-month availability traces from three different Internet applications. Building upon this, we show how our probabilistic approach makes it easy to evaluate and optimize the performance in a number of diverse network application models and to use them to optimize systems. In particular, we show how this approach can be used in distributed hash tables, friend-to-friend storage, and cache preloading for social networks, resulting in substantial gains in data availability and system efficiency at negligible costs.

Solutions based on service-oriented architecture are gaining popularity. However a wider adoption, especially for business critical functions, is hampered by the trust deficit that exists between consumers and providers, as consumers are shielded from the service architectures and the operation of the service itself. Security certification can be used as a means to bridge this trust deficit. Common Criteria for Information Technology Evaluation (CC) is a widely recognized and used security certification scheme. However, the CC scheme was tailored to provide assurance for traditional software provisioning models and hence cannot be applied to SOA solutions as is. In this paper, we present the limitations of the CC scheme when applied in SOA, the challenges that must be overcome for its adoption and possible directions through which some of those challenges can be met. In particular, we point out that CC scheme should be extended to allow for dynamic evaluation of deployed systems (which includes the operational environment) and for handling assurance of composite services.

The security and dependability of cloud applications require strong confidence in the communication protocol used to access web resources. The mainstream service providers nowadays are shifting to REST-based services in the detriment of SOAP-based ones. REST proposes a lightweight approach to consume resources with no specific encapsulation, thus lacking of meta-data descriptions for security requirements. Currently, the security of RESTful services relies on ad-hoc security mechanisms (whose implementation is error-prone) or on the transport layer security (offering poor flexibility). We introduce the REST security protocol to provide secure service communication, together with its performance analysis when compared to equivalent WS-Security configuration.

The expected high complexity in future automotive applications will require to frequently update electronic devices supporting those applications. Even if in-car devices are trusted, potential attacks on over the air exchanges impose stringent requirements on both safety and security. To address the formal verification of safety properties, we have previously introduced the AVATAR UML profile whose methodology covers requirement, analysis, design, and formal verification stages [1]. We now propose to extend AVATAR to support both safety and security during all methodological stages, and in the same models. The paper applies the extended AVATAR to an over the-air protocol for trusted firmware updates of in-car control units, with a special focus on design and formal verification stages.

The effectiveness of Car2X communication strongly relies on trust in received data. Securing in-vehicle communication is an essential yet so far overlooked step to achieve this objective. We present an approach based on the use of symmetric key material protected with inexpensive hardware. We modeled the involved cryptographic and network protocols, showed their applicability to automotive bus systems and conclude about their soundness with analytical and simulation methods. A prototype realization in real vehicles is envisaged as part of an ongoing project.

It is a well known fact that user-chosen passwords are somewhat predictable: by using tools such as dictionaries or probabilistic models, attackers and password recovery tools can drastically reduce the number of attempts needed to guess a password. Quite surprisingly, however, existing literature does not provide a satisfying answer to the following question: given a number of guesses, what is the probability that a state-of-the-art attacker will be able to break a password? To answer the former question, we compare and evaluate the effectiveness of currently known attacks using various datasets of known passwords. We find that a "diminishing returns" principle applies: in the absence of an enforced password strength policy, weak passwords are common; on the other hand, as the attack goes on, the probability that a guess will succeed decreases by orders of magnitude. Even extremely powerful attackers won't be able to guess a substantial percentage of the passwords. The result of this work will help in evaluating the security of authentication means based on user- chosen passwords, and our methodology for estimating password strength can be used as a basis for creating more effective proactive password checkers for users and security auditing tools for administrators.

Collaborating on complex XML data structures is a nontrivial task in domains such as the public sector,healthcare or engineering. Specifically, providing scalable XML content dissemination services in a selective and secure fashion is a challenging task. This paper describes a publish/subscribe middleware infrastructure to achieve a content-based dissemination of XML documents. Our approach relies on the dissemination of XML documents based on their semantics, as described by concepts that form an interoperable description of documents. This infrastructure leverages our earlier scheme for protecting the integrity and confidentiality of XML content during dissemination.

Comparing different versions of large tree structured data is a CPU and memory intensive task. State of the art techniques require the complete XML trees and their internal representations to be loaded into memory before any comparison may start. Furthermore, comparing sanitized XML trees is not addressed by these techniques. We propose a comparison technique for sanitized XML documents which ultimately results into a minimum cost edit script transforming the initial tree into the target tree. This method uses encrypted integer labels to encode the original XML structure and content, making the encrypted XML readable only by a legitimate party. Encoded tree nodes can be compared by a third party with a limited intermediate representation.

This paper introduces a distributed and fine grained access control mechanism based on encryption for XML document centric collaborative applications. This mechanism also makes it possible to simultaneously protect the confidentiality of a document and to verify its authenticity and integrity, as well to trace its updates. The enforcement of access control is distributed to participants and does not rely on a central authority. Novel aspects of the proposed framework include the adoption of a decentralized key management scheme to support the client-based enforcement of the access control policy. This scheme is driven by the expression of access patterns of interest of the participants over document parts to determine the keys required. A lazy rekeying protocol is also defined to accommodate the delegation of access control decisions that in particular reduces rekeying latency when faced with the addition and removal of participants.

Reputation systems have demonstrated their interest in stimulating cooperation in peer-to-peer (P2P) systems. Their key operation relies on collecting, processing, and disseminating the feedback about some peers' past behavior in order to boost their cooperation, albeit this is susceptible to collusion and bashing. Additionally, estimating reputation generally relies on a partial assessment of the behavior of peers only, which might delay the detection of selfish peers. This situation is rendered even worse in self-organized storage applications, since storage is not an instantaneous operation and data are vulnerable throughout their entire storage lifetime. This paper compares reputation to an audit-based approach where peer observations are carried out through the periodic verification of a proof of data possession, and shows how the latter approach better addresses the aforementioned issues of inciting cooperation in P2P storage.

This paper discusses how to model a protocol for the verification of data possession intended to secure a peer-to-peer storage application. The verification protocol is a primitive for storage assessment, and indirectly motivates nodes to behave cooperatively within the application. The capability of the protocol to enforce cooperation between a data holder and a data owner is proved theoretically by modeling the verification protocol as a Bayesian game, and demonstrating that the solution of the game is an equilibrium where both parties are cooperative.