Abstract Focusing is a known technique for reducing the number of proofs while preserving derivability. Skolemisation is another technique designed to improve proof search, which reduces the number of back-tracking steps by representing dependencies on the term level and instantiate witness terms during unification at the axioms or fail with an occurs-check otherwise. Skolemisation for classical logic is well understood, but a practical skolemisation procedure for focused intuitionistic linear logic has been elusive so far. In this paper we present a focused variant of first-order intuitionistic linear logic together with a sound and complete skolemisation procedure.

Recent technical advances in utility computing have allowed mall and medium sized businesses to move their applications to the cloud, to benefit from features such as auto-scaling and pay-as-you-go facilities. Before clouds are widely adopted, there is a need to address privacy concerns of customer data outsourced to these platforms. In this paper, we present a practical approach for protecting the confidentiality and integrity of client data and computation from insider attacks such as cloud clients as well as from the Infrastructure-as-a-Service (IaaS) based cloud system administrator himself. We demonstrate a scenario of how the origin integrity and authenticity of health-care multimedia content processed on the cloud can be verified using digital watermarking in an isolated environment without revealing the watermark details to the cloud administrator. Finally to verify that our protocol does not compromise confidentiality and integrity of the client data and computation or degrade performance, we have tested a prototype system using two different approaches. Formal verification using ProVerif tool shows that cryptographic operations and protocol communication cannot be compromised using a realistic attacker model. Performance analysis of our implementation demonstrates that it adds negligible overhead.

We present StatVerif, which is an extension of the ProVerif process calculus with constructs for explicit state, in order to be able to reason about protocols that manipulate global state. Global state is required by protocols used in hardware devices (such as smart cards and the trusted platform m odule), as well as by protocols involving databases that store persistent information. We provide the operational semantics of StatVerif. We extend the ProVerif compiler to a compiler for StatVerif, which takes processes written in the extended process language and produces Horn clauses. Our compilation is carefully engineered to avoid many false attacks. We prove the correctness of the StatVerif compiler. We illustrate our method on two examples: a small hardware security device and a contract signing protocol. We are able to prove their desired properties automatically.

The matrix method, due to Bibel and Andrews, is a proof procedure designed for automated theorem-proving. We show that underlying this method is a fully structured combinatorial model of conventional classical proof theory.

Mobile telephony equipment is daily carried by billions of subscribers everywhere they go. Avoiding linkability of subscribers by third parties, and protecting the privacy of those subscribers is one of the goals of mobile telecommunication protocols. We use formal methods to model and analyse the security properties of 3G protocols. We expose two novel threats to the user privacy in 3G telephony systems, which make it possible to trace and identify mobile telephony subscribers, and we demonstrate the feasibility of a low cost implementation of these attacks. We propose fixes to these privacy issues, which also take into account and solve other privacy attacks known from the literature. We successfully prove that our privacy-friendly fixes satisfy the desired unlinkability and anonymity properties using the automatic verification tool ProVerif.

We present StatVerif, which is an extension the ProVerif process calculus with constructs for explicit state, in order to be able to reason about protocols that manipulate global state. Global state is required by protocols used in hardware devices (such as smart cards and the TPM), as well as by protocols involving databases that store persistent information. We provide the operational semantics of StatVerif. We extend the ProVerif compiler to a compiler for StatVerif: it takes processes written in the extended process language, and produces Horn clauses. Our compilation is carefully engineered to avoid many false attacks. We prove the correctness of the StatVerif compiler. We illustrate our method on two examples: a small hardware security device, and a contract signing protocol. We are able to prove their desired properties automatically.

An attacker that can identify messages as coming from the same source, can use this information to build up a picture of targets' behaviour, and so, threaten their privacy. In response to this danger, unlinkable protocols aim to make it impossible for a third party to identify two runs of a protocol as coming from the same device. We present a framework for analysing unlinkability and anonymity in the applied pi calculus. We show that unlinkability and anonymity are complementary properties; one does not imply the other. Using our framework we show that the French RFID e-passport preserves anonymity but it is linkable therefore anyone carrying a French e-passport can be physically traced.

We extend Parigot's λμ-calculus to form a system of realizers for classical logic which reflects the structure of Gentzen's cut-free, multiple-conclusioned, sequent calculus LK when used as a system for proof-search. Specifically, we add (i) a second binding operator, υ, which realizes classical, multiple-conclusioned disjunction, and (ii) explicit substitutions, ∈, which provide sufficient term-structure to interpret the left rules of LK. A necessary and sufficient condition is formulated on realizers to characterize when a given (classical) realizer for a sequent witnesses the intuitionistic provability of that sequent. A translation between the classical sequent calculus and classical resolution due to Mints is used to lift the conditions to classical resolution, thereby giving a characterization of the intuitionistic force of classical resolution. One application of these results is to allow standard resolution methods of uniform proof-search to be used directly for intuitionistic logic but, more significantly, they support a type-theoretic analysis of search spaces in both classical and intuitionistic logic.