Model-driven Information Flow Security for Component-Based Systems

International audienceThis paper proposes a formal framework for studying information flow security in component-based systems. The security policy is defined and verified from the early steps of the system design. Two kinds of non-interference properties are formally introduced and for both of them, sufficient conditions that ensures and simplifies the automated verification are proposed. The verification is compositional, first locally, by checking the behavior of every atomic component and then globally, by checking the inter-components communication and coordination. The potential benefits are illustrated on a concrete case study about constructing secure heterogeneous distributed systems

Composition and Declassification in Possibilistic Information Flow Security

Formal methods for security can rule out whole classes of security vulnerabilities, but applying them in practice remains challenging. This thesis develops formal verification techniques for information flow security that combine the expressivity and scalability strengths of existing frameworks. It builds upon Bounded Deducibility (BD) Security, which allows specifying and verifying fine-grained policies about what information may flow when to whom. Our main technical result is a compositionality theorem for BD Security, providing scalability by allowing us to verify security properties of a large system by verifying smaller components. Its practical utility is illustrated by a case study of verifying confidentiality properties of a distributed social media platform. Moreover, we discuss its use for the modular development of secure workflow systems, and for the security-preserving enforcement of safety and security properties other than information flow control

Action Systems, Determinism and the Development of Secure Systems

This thesis addresses issues arising in the specification and development of secure systems, focusing in particular on aspects of confidentiality. Various confidentiality properties based on limiting the allowed flows of information in a system have previously been proposed. These definitions axe reviewed here and some of the problems inherent in their use axe outlined. Recent work by Roscoe [106] has. provided information flow definitions based on restricting the allowed nondeterminism within the system. These properties axe described in detail, with a range of examples provided to illustrate their use.This thesis is concerned with providing a new, pragmatic approach to the development of secure systems. Action systems axe chosen as a notation which incorporates both direct representation of system state useful for effective system modelling and the succession of events in a system essential for representation of information flow properties. A definition of nondeterminism and formulations of the deterministic security properties axe developed for action systems. These axe shown to correspond to the original CSP event based definitions.The emphasis of this work is on the practical application of theoretical results. This is reflected in the case studies in which the preceding work is applied to realistic development situations. This allows the strengths and weaknesses of both the deterministic security conditions and the use of action systems to be assessed. The first study investigates security constraints applied to a distributed message-passing system. Ways of specifying security conditions and the effects of including them at different levels axe explored. The second case study follows through the specification and refinement of a distributed security kernel. A technique for the simplification of security proofs is introduced

Secure Information Flow via Stripping and Fast Simulation

Type systems for secure information flow aim to prevent a program from leaking information from H (high) to L (low) variables. Traditionally, bisimulation has been the prevalent technique for proving the soundness of such systems. This work intro- duces a new proof technique based on stripping and fast simulation, and shows that it can be applied in a number of cases where bisimulation fails. We present a progressive development of this technique over a representative sample of languages includ- ing a simple imperative language (core theory), a multiprocessing nondeterministic language, a probabilistic language, and a language with cryptographic primitives. In the core theory we illustrate the key concepts of this technique in a basic setting. A fast low simulation in the context of transition systems is a binary relation where simulating states can match the moves of simulated states while maintaining the equivalence of low variables; stripping is a function that removes high commands from programs. We show that we can prove secure information flow by arguing that the stripping relation is a fast low simulation. We then extend the core theory to an abstract distributed language under a nondeterministic scheduler. Next, we extend to a probabilistic language with a random assignment command; we generalize fast simulation to the setting of discrete time Markov Chains, and prove approximate probabilistic noninterference. Finally, we introduce cryptographic primitives into the probabilistic language and prove computational noninterference, provided that the underling encryption scheme is secure

On Secure Workflow Decentralisation on the Internet

Decentralised workflow management systems are a new research area, where most work to-date has focused on the system's overall architecture. As little attention has been given to the security aspects in such systems, we follow a security driven approach, and consider, from the perspective of available security building blocks, how security can be implemented and what new opportunities are presented when empowering the decentralised environment with modern distributed security protocols. Our research is motivated by a more general question of how to combine the positive enablers that email exchange enjoys, with the general benefits of workflow systems, and more specifically with the benefits that can be introduced in a decentralised environment. This aims to equip email users with a set of tools to manage the semantics of a message exchange, contents, participants and their roles in the exchange in an environment that provides inherent assurances of security and privacy. This work is based on a survey of contemporary distributed security protocols, and considers how these protocols could be used in implementing a distributed workflow management system with decentralised control . We review a set of these protocols, focusing on the required message sequences in reviewing the protocols, and discuss how these security protocols provide the foundations for implementing core control-flow, data, and resource patterns in a distributed workflow environment

Combining behavioural types with security analysis

Today's software systems are highly distributed and interconnected, and they increasingly rely on communication to achieve their goals; due to their societal importance, security and trustworthiness are crucial aspects for the correctness of these systems. Behavioural types, which extend data types by describing also the structured behaviour of programs, are a widely studied approach to the enforcement of correctness properties in communicating systems. This paper offers a unified overview of proposals based on behavioural types which are aimed at the analysis of security properties