No abstract

Part 1: PrivacyInternational audienceThis paper proposes an approach to verify information flow security of concurrent programs. It discusses a hyperproperty called observational determinism which aims to ensure secure information flow in concurrent programs, and proves how this hyperproperty can be verified by stutter equivalence checking. More precisely, it defines observational determinism in terms of stutter equivalence of all traces having the same low initial value and shows how stutter trace equivalence can be verified by computing a divergence stutter bisimulation quotient. The approach is illustrated by verifying a small example

No abstract

Preserving the confidentiality of information is a growing concern in software development. Secure information flow is intended to maintain the confidentiality of sensitive information by preventing them from flowing to attackers. This paper discusses how to ensure confidentiality for multi-threaded programs through a property called observational determinism. Operational semantics of multi-threaded programs are modeled using Kripke structures. Observational determinism is formalized in terms of divergence weak low-bisimulation. Bisimulation is an equivalence relation associating executions that simulate each other. The new property is called bisimulation-based observational determinism. Furthermore, a model checking method is proposed to verify the new property and ensure that secure information flow holds in a multi-threaded program. The model checking method successively refines the Kripke model of the program until the quotient of the model with respect to divergence weak low-bisimulation is reached. Then, bisimulation-based observational determinism is checked on the quotient, which is a minimized model of the concrete Kripke model. The time complexity of the proposed method is polynomial in the size of the Kripke model. The proposed approach has been implemented on top of PRISM, a probabilistic model checking tool. Finally, a case study is discussed to show the applicability of the proposed approach.

Peer-to-peer networks have emerged as a common method for sharing large amounts of data. The main challenge in these networks is efficiently locating information distributed across the hosts/peers of the network by decentralized approach. In this paper, first we refer to the Chord protocol that is a distributed lookup service, and then propose a new method, called CLTChord, to optimize this protocol. In this new method, in addition to using the local finger tables for routing requests, the cache location tables are used, in which each node stores nodes which are at its close geographical range. When a node receives a new request, it first checks its cache location table and if a desired response is not received, the algorithm continues to work like the basic Chord protocol. Our simulation shows that this optimization improves the parameters of the hop count, the lookup latencies and number of the sent packets; In this paper, hop count is the distance between the source node which initiates the lookup and the target node which has the desired value; and latency is the duration of time needed for resolving file lookups from the time when it was initiated until it was responded to (measured in milliseconds)