Parameterized Verification of Safety Properties in Ad Hoc Network Protocols

We summarize the main results proved in recent work on the parameterized verification of safety properties for ad hoc network protocols. We consider a model in which the communication topology of a network is represented as a graph. Nodes represent states of individual processes. Adjacent nodes represent single-hop neighbors. Processes are finite state automata that communicate via selective broadcast messages. Reception of a broadcast is restricted to single-hop neighbors. For this model we consider a decision problem that can be expressed as the verification of the existence of an initial topology in which the execution of the protocol can lead to a configuration with at least one node in a certain state. The decision problem is parametric both on the size and on the form of the communication topology of the initial configurations. We draw a complete picture of the decidability and complexity boundaries of this problem according to various assumptions on the possible topologies.Comment: In Proceedings PACO 2011, arXiv:1108.145

An Audit Logic for Accountability

We describe and implement a policy language. In our system, agents can distribute data along with usage policies in a decentralized architecture. Our language supports the specification of conditions and obligations, and also the possibility to refine policies. In our framework, the compliance with usage policies is not actively enforced. However, agents are accountable for their actions, and may be audited by an authority requiring justifications.Comment: To appear in Proceedings of IEEE Policy 200

A mechanized proof of loop freedom of the (untimed) AODV routing protocol

The Ad hoc On-demand Distance Vector (AODV) routing protocol allows the nodes in a Mobile Ad hoc Network (MANET) or a Wireless Mesh Network (WMN) to know where to forward data packets. Such a protocol is 'loop free' if it never leads to routing decisions that forward packets in circles. This paper describes the mechanization of an existing pen-and-paper proof of loop freedom of AODV in the interactive theorem prover Isabelle/HOL. The mechanization relies on a novel compositional approach for lifting invariants to networks of nodes. We exploit the mechanization to analyse several improvements of AODV and show that Isabelle/HOL can re-establish most proof obligations automatically and identify exactly the steps that are no longer valid.Comment: The Isabelle/HOL source files, and a full proof document, are available in the Archive of Formal Proofs, at http://afp.sourceforge.net/entries/AODV.shtm

A Type-Safe Model of Adaptive Object Groups

Services are autonomous, self-describing, technology-neutral software units that can be described, published, discovered, and composed into software applications at runtime. Designing software services and composing services in order to form applications or composite services requires abstractions beyond those found in typical object-oriented programming languages. This paper explores service-oriented abstractions such as service adaptation, discovery, and querying in an object-oriented setting. We develop a formal model of adaptive object-oriented groups which offer services to their environment. These groups fit directly into the object-oriented paradigm in the sense that they can be dynamically created, they have an identity, and they can receive method calls. In contrast to objects, groups are not used for structuring code. A group exports its services through interfaces and relies on objects to implement these services. Objects may join or leave different groups. Groups may dynamically export new interfaces, they support service discovery, and they can be queried at runtime for the interfaces they support. We define an operational semantics and a static type system for this model of adaptive object groups, and show that well-typed programs do not cause method-not-understood errors at runtime.Comment: In Proceedings FOCLASA 2012, arXiv:1208.432

TAPAs: A Tool for the Analysis of Process Algebras

Process algebras are formalisms for modelling concurrent systems that permit mathematical reasoning with respect to a set of desired properties. TAPAs is a tool that can be used to support the use of process algebras to specify and analyze concurrent systems. It does not aim at guaranteeing high performances, but has been developed as a support to teaching. Systems are described as process algebras terms that are then mapped to labelled transition systems (LTSs). Properties are verified either by checking equivalence of concrete and abstract systems descriptions, or by model checking temporal formulae over the obtained LTS. A key feature of TAPAs, that makes it particularly suitable for teaching, is that it maintains a consistent double representation of each system both as a term and as a graph. Another useful didactical feature is the exhibition of counterexamples in case equivalences are not verified or the proposed formulae are not satisfied

Compositional verification of integrity for digital stream signature protocols

We investigate the application of concurrency theory notions as simulation relations and compositional proof rules for verifying digital stream signature protocols. In particular, we formally prove the integrity of the Gennaro-Rohatgi protocols in [7]. As a peculiarity, our technique is able to check a protocol with an unbounded number of parallel processes. We argue also that our approach may be applied to a wider class of stream signature protocols

Formal models and analysis of secure multicast in wired and wireless networks

The spreading of multicast technology enables the development of group communication and so dealing with digital streams becomes more and more common over the Internet. Given the flourishing of security threats, the distribution of streamed data must be equipped with sufficient security guarantees. To this aim, some architectures have been proposed, to supply the distribution of the stream with guarantees of, e.g., authenticity, integrity, and confidentiality of the digital contents. This paper shows a formal capability of capturing some features of secure multicast protocols. In particular, both the modeling and the analysis of some case studies are shown, starting from basic schemes for signing digital streams, passing through proto- cols dealing with packet loss and time-synchronization requirements, concluding with a secure distribution of a secret key. A process-algebraic framework will be exploited, equipped with schemata for analysing security properties and compositional principles for evaluating if a property is satisfied over a system with more than two components

Automated Verification of Asynchronous Communicating Systems with TLA+

Verifying the compatibility of communicating peers is a crucial issue in critical distributed systems. Unlike the synchronous world, the asynchronous world covers a wide range of message ordering paradigms (e.g. FIFO or causal) that are instrumental to the compatibility of peer compositions. We propose a framework that takes into account the variety of asynchronous communication models and compatibility properties. The notions of peer, communication model, system and compatibility criteria are formalized in TLA+ to benefit from its verification tools. We present an implemented toolchain that generates TLA+ specifications from the behavioral descriptions of peers and checks compatibility of the composition with respect to given communication models and compatibility criteria