105,044 research outputs found
Towards Efficient Verification of Population Protocols
Population protocols are a well established model of computation by
anonymous, identical finite state agents. A protocol is well-specified if from
every initial configuration, all fair executions reach a common consensus. The
central verification question for population protocols is the
well-specification problem: deciding if a given protocol is well-specified.
Esparza et al. have recently shown that this problem is decidable, but with
very high complexity: it is at least as hard as the Petri net reachability
problem, which is EXPSPACE-hard, and for which only algorithms of non-primitive
recursive complexity are currently known.
In this paper we introduce the class WS3 of well-specified strongly-silent
protocols and we prove that it is suitable for automatic verification. More
precisely, we show that WS3 has the same computational power as general
well-specified protocols, and captures standard protocols from the literature.
Moreover, we show that the membership problem for WS3 reduces to solving
boolean combinations of linear constraints over N. This allowed us to develop
the first software able to automatically prove well-specification for all of
the infinitely many possible inputs.Comment: 29 pages, 1 figur
Guidelines for Verification of Population Protocols
We address the problem of verification by model-checking of the basic population protocol (\pp) model of Angluin et al. This problem has received special attention the last two years and new tools have been proposed to deal with it. We show that the problem can be solved using the existing model-checking tools, e.g., Spin and Prism. For this, we apply the counting abstraction to obtain an abstract model of a \pp\ which can be efficiently verified by the existing model-checking tools. Moreover, this abstraction preserves the correct stabilization property of \pp. To deal with the fairness assumed in the \pp\ model, we provide two recipes. The first one gives sufficient conditions under which the \pp\ fairness can be replaced by the weak fairness implemented in Spin. We show that this recipe can be applied to several \pp\ models. In the second recipe, we show how to use the probabilistic model-checking and the tool Prism to deal completely with the fairness of the \pp\ model. The correctness of this recipe is based on existing theorems on finite discrete Markov chains
Verification of Immediate Observation Population Protocols
Population protocols (Angluin et al., PODC, 2004) are a formal model of sensor networks consisting of identical mobile devices. Two devices can interact and thereby change their states. Computations are infinite sequences of interactions satisfying a strong fairness constraint.
A population protocol is well-specified if for every initial configuration C of devices, and every computation starting at C, all devices eventually agree on a consensus value depending only on C. If a protocol is well-specified, then it is said to compute the predicate that assigns to each initial configuration its consensus value.
In a previous paper we have shown that the problem whether a given protocol is well-specified and the problem whether it computes a given predicate are decidable. However, in the same paper we prove that both problems are at least as hard as the reachability problem for Petri nets. Since all known algorithms for Petri net reachability have non-primitive recursive complexity, in this paper we restrict attention to immediate observation (IO) population protocols, a class introduced and studied in (Angluin et al., PODC, 2006). We show that both problems are solvable in exponential space for IO protocols. This is the first syntactically defined, interesting class of protocols for which an algorithm not requiring Petri net reachability is found
Expressive Power of Broadcast Consensus Protocols
Population protocols are a formal model of computation by identical, anonymous mobile agents interacting in pairs. Their computational power is rather limited: Angluin et al. have shown that they can only compute the predicates over N^k expressible in Presburger arithmetic. For this reason, several extensions of the model have been proposed, including the addition of devices called cover-time services, absence detectors, and clocks. All these extensions increase the expressive power to the class of predicates over N^k lying in the complexity class NL when the input is given in unary. However, these devices are difficult to implement, since they require that an agent atomically receives messages from all other agents in a population of unknown size; moreover, the agent must know that they have all been received. Inspired by the work of the verification community on Emerson and Namjoshi\u27s broadcast protocols, we show that NL-power is also achieved by extending population protocols with reliable broadcasts, a simpler, standard communication primitive
An Approach to Model Checking of Multi-agent Data Analysis
The paper presents an approach to verification of a multi-agent data analysis
algorithm. We base correct simulation of the multi-agent system by a finite
integer model. For verification we use model checking tool SPIN. Protocols of
agents are written in Promela language and properties of the multi-agent data
analysis system are expressed in logic LTL. We run several experiments with
SPIN and the model.Comment: In Proceedings MOD* 2014, arXiv:1411.345
How to Work with Honest but Curious Judges? (Preliminary Report)
The three-judges protocol, recently advocated by Mclver and Morgan as an
example of stepwise refinement of security protocols, studies how to securely
compute the majority function to reach a final verdict without revealing each
individual judge's decision. We extend their protocol in two different ways for
an arbitrary number of 2n+1 judges. The first generalisation is inherently
centralised, in the sense that it requires a judge as a leader who collects
information from others, computes the majority function, and announces the
final result. A different approach can be obtained by slightly modifying the
well-known dining cryptographers protocol, however it reveals the number of
votes rather than the final verdict. We define a notion of conditional
anonymity in order to analyse these two solutions. Both of them have been
checked in the model checker MCMAS
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