Set Of Possible Executions Research Articles

Correctness of the Chord protocol

Internet of Things (IoT) can be seen as a cooperation of various devices with limited performances that participate in the same system. IoT devices compose a distributed architecture system. The core of every IoT system is its discovery and control services. To realize such services, some authors used the developed solutions from the different domains. One such solution is the Chord protocol, one of the first, the simplest and the most popular distributed protocols. Unfortunately, the application of the Chord protocol was realized using the correctness of the Chord protocol for granted, or by the very hard assumptions. In this paper we prove the correctness of the Chord protocol using the logic of time and knowledge with the respect to the set of possible executions, called regular runs. We provide the deterministic description of the correctness of the Chord protocol and consider Chord actions that maintain ring topology while the nodes can freely join or leave.

Deducibility constraints and blind signatures

Deducibility constraints represent in a symbolic way the infinite set of possible executions of a finite protocol. Solving a deducibility constraint amounts to finding all possible ways of filling the gaps in a proof. For finite local inference systems, there is an algorithm that reduces any deducibility constraint to a finite set of solved forms. This allows one to decide any trace security property of cryptographic protocols.We investigate here the case of infinite local inference systems, through the case study of blind signatures. We show that, in this case again, any deducibility constraint can be reduced to finitely many solved forms (hence we can decide trace security properties). We sketch also another example to which the same method can be applied.

Extending the enforcement power of truncation monitors using static analysis

Runtime monitors are a widely used approach to enforcing security policies. Truncation monitors are based on the idea of truncating an execution before a violation occurs. Thus, the range of security policies they can enforce is limited to safety properties. The use of an a priori static analysis of the target program is a possible way of extending the range of monitorable properties. This paper presents an approach to producing an in-lined truncation monitor, which draws upon the above intuition. Based on an a priori knowledge of the program behavior, this approach allows, in some cases, to enforce more than safety properties and is more powerful than a classical truncation mechanism. We provide and prove a theorem stating that a truncation enforcement mechanism considering only the set of possible executions of a specific program is strictly more powerful than a mechanism considering all the executions over an alphabet of actions.

Semantic adaptation of multimedia documents

Multimedia documents have to be played on multiple device types. Hence, usage and platform diversity requires document adaptation according to execution contexts, not generally predictable at design time. In an earlier work, a semantic framework for multimedia document adaptation was proposed. In this framework, a multimedia document is interpreted as a set of potential executions corresponding to the author specification. To each target device corresponds a set of possible executions complying with the device constraints. In this context, adapting requires to select an execution that satisfies the target device constraints and which is as close as possible from the initial composition. This theoretical adaptation framework does not specifically consider the main multimedia document dimensions, i.e., temporal, spatial and hypermedia. In this paper, we propose a concrete application of this framework on standard multimedia documents. For that purpose, we first define an abstract structure that captures the spatio-temporal and hypermedia dimensions of multimedia documents, and we develop an adaptation algorithm which transforms in a minimal way such a structure according to device constraints. Then, we show how this can be used for adapting concrete multimedia documents in SMIL through converting the documents in the abstract structure, using the adaptation algorithm, and converting it back in SMIL. This can be used for other document formats without modifying the adaptation algorithm.

Data-race and concurrent-write freedom are undecidable

In a distributed shared memory system, sequential consistency is often assumed as the model for the memory, because it is a natural extension from multitasking in uniprocessor systems. Weaker consistency models allow greater concurrency, but programming is harder, because programs may produce unexpected results. Data-race-free (DRF) and concurrent-write-free (CWF) programs have the same set of possible executions both under a sequentially consistent memory and under some other, weaker model, memories. They can be written for a sequential memory and run unchanged under such a weaker-model memory. Since the sets of possible executions are the same, the run will only produce results that are possible under sequential consistency. This article proves the undecidability of both classes of concurrent programs in a language with if statements, loops, barriers, dynamic process creation, dynamic storage, and recursive data structures, under many models weaker than sequential consistency. Moreover, the article also proves that methods that only add synchronization statements to programs written for sequential consistency must produce some conservatively DRF or CWF programs.