Our growing dependence on increasingly complex computer and software systems necessitates the development of formalisms, techniques, and tools for assessing functional properties of these systems. One such technique that has emerged in the last twenty years is model checking, which systematically (and automatically) checks whether a model of a given system satisfies a desired property such as deadlock freedom, invariants, and request-response properties. This automated technique for verification and debugging has developed into a mature and widely used approach with many applications. Principles of Model Checking offers a comprehensive introduction to model checking that is not only a text suitable for classroom use but also a valuable reference for researchers and practitioners in the field. The book begins with the basic principles for modeling concurrent and communicating systems, introduces different classes of properties (including safety and liveness), presents the notion of fairness, and provides automata-based algorithms for these properties. It introduces the temporal logics LTL and CTL, compares them, and covers algorithms for verifying these logics, discussing real-time systems as well as systems subject to random phenomena. Separate chapters treat such efficiency-improving techniques as abstraction and symbolic manipulation. The book includes an extensive set of examples (most of which run through several chapters) and a complete set of basic results accompanied by detailed proofs. Each chapter concludes with a summary, bibliographic notes, and an extensive list of exercises of both practical and theoretical nature.

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Principles of Model Checking

In Distributed Algorithms, Nancy Lynch provides a blueprint for designing, implementing, and analyzing distributed algorithms. She directs her book at a wide audience, including students, programmers, system designers, and researchers.



Distributed Algorithms contains the most significant algorithms and impossibility results in the area, all in a simple automata-theoretic setting. The algorithms are proved correct, and their complexity is analyzed according to precisely defined complexity measures. The problems covered include resource allocation, communication, consensus among distributed processes, data consistency, deadlock detection, leader election, global snapshots, and many others.



The material is organized according to the system model-first by the timing model and then by the interprocess communication mechanism. The material on system models is isolated in separate chapters for easy reference.



The presentation is completely rigorous, yet is intuitive enough for immediate comprehension. This book familiarizes readers with important problems, algorithms, and impossibility results in the area: readers can then recognize the problems when they arise in practice, apply the algorithms to solve them, and use the impossibility results to determine whether problems are unsolvable. The book also provides readers with the basic mathematical tools for designing new algorithms and proving new impossibility results. In addition, it teaches readers how to reason carefully about distributed algorithms-to model them formally, devise precise specifications for their required behavior, prove their correctness, and evaluate their performance with realistic measures.


Table of Contents

1 Introduction 
2 Modelling I; Synchronous Network Model 
3 Leader Election in a Synchronous Ring 
4 Algorithms in General Synchronous Networks 
5 Distributed Consensus with Link Failures 
6 Distributed Consensus with Process Failures 
7 More Consensus Problems 
8 Modelling II: Asynchronous System Model 
9 Modelling III: Asynchronous Shared Memory Model 
10 Mutual Exclusion 
11 Resource Allocation 
12 Consensus 
13 Atomic Objects 
14 Modelling IV: Asynchronous Network Model 
15 Basic Asynchronous Network Algorithms 
16 Synchronizers 
17 Shared Memory versus Networks 
18 Logical Time 
19 Global Snapshots and Stable Properties 
20 Network Resource Allocation 
21 Asynchronous Networks with Process Failures 
22 Data Link Protocols 
23 Partially Synchronous System Models 
24 Mutual Exclusion with Partial Synchrony 
25 Consensus with Partial Synchrony

Distributed algorithms

We propose a novel paradigm for defining security of cryptographic protocols, called universally composable security. The salient property of universally composable definitions of security is that they guarantee security even when a secure protocol is composed of an arbitrary set of protocols, or more generally when the protocol is used as a component of an arbitrary system. This is an essential property for maintaining security of cryptographic protocols in complex and unpredictable environments such as the Internet. In particular, universally composable definitions guarantee security even when an unbounded number of protocol instances are executed concurrently in an adversarially controlled manner, they guarantee non-malleability with respect to arbitrary protocols, and more. We show how to formulate universally composable definitions of security for practically any cryptographic task. Furthermore, we demonstrate that practically any such definition can be realized using known techniques, as long as only a minority of the participants are corrupted. We then proceed to formulate universally composable definitions of a wide array of cryptographic tasks, including authenticated and secure communication, key-exchange, public-key encryption, signature, commitment, oblivious transfer, zero knowledge and more. We also make initial steps towards studying the realizability of the proposed definitions in various settings.

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Universally composable security: a new paradigm for cryptographic protocols

This paper describes a major new release of the PRISMprobabilistic model checker, adding, in particular, quantitative verification of (priced) probabilistic timed automata. These model systems exhibiting probabilistic, nondeterministic and real-time characteristics. In many application domains, all three aspects are essential; this includes, for example, embedded controllers in automotive or avionic systems, wireless communication protocols such as Bluetooth or Zigbee, and randomised security protocols. PRISM, which is open-source, also contains several new components that are of independent use. These include: an extensible toolkit for building, verifying and refining abstractions of probabilistic models; an explicit-state probabilistic model checking library; a discrete-event simulation engine for statistical model checking; support for generation of optimal adversaries/strategies; and a benchmark suite.

http://www.prismmodelchecker.org/papers/cav11.pdf

PRISM 4.0: verification of probabilistic real-time systems

Usually, a proof of a theorem contains more knowledge than the mere fact that the theorem is true. For instance, to prove that a graph is Hamiltonian it suffices to exhibit a Hamiltonian tour in it; however, this seems to contain more knowledge than the single bit Hamiltonian/non-Hamiltonian.In this paper a computational complexity theory of the “knowledge” contained in a proof is developed. Zero-knowledge proofs are defined as those proofs that convey no additional knowledge other than the correctness of the proposition in question. Examples of zero-knowledge proof systems are given for the languages of quadratic residuosity and 'quadratic nonresiduosity. These are the first examples of zero-knowledge proofs for languages not known to be efficiently recognizable.

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The knowledge complexity of interactive proof-systems

Several probabilistic simulation relations for probabili stic systems are defined and evaluated according to two criteria: compositionality and preservation of "interesting" properties. Here, the interesting properties of a system are identified with those that are expressible in an untimed version of the Timed Probabilistic concurrent Computation Tree Logic (TPCTL) of Hansson. The definitions are made, and the evaluations carried out, in terms of a general labeled transition system model for concurrent probabilistic computation. The results cover weak simulations, which abstract from internal computation, as well as strong simulations, which do not

Probabilistic simulations for probabilistic processes

Randomization is an excellent tool for the design of distributed algorithms, sometimes yielding efficient solutions to problems that are inherently complex, or even unsolvable, in the setting of deterministic algorithms. However, this tool has a price: even simple randomized algorithms can be extremely hard to verify and analyze. This thesis addresses the problem of verification of randomized distributed algorithms. We consider the problem both from the theoretical and the practical perspective. Our theoretical work builds a new mathematical model of randomized distributed computation; our practical work develops techniques to be used for the actual verification of randomized systems. Our analysis involves both untimed and timed systems, so that real-time properties can be investigated. Our model for randomized distributed computation is an extension of labeled transition systems. A Probalistic automation is a state machine with transitions, where, unlike for labeled transitions systems, a transition from a state leads to a discrete probability distribution over pairs consisting of a label and a state, rather than to a single label and a single state. A probalistic automation contains pure nondeterministic behavior since from each state there can be several transisitions, and probalistic behavior since once a transaction is chosen the label that occurs and the state that is reached are determined by a probability distribution. The resolution of pure nondeterminism leads to probalistic executions, which are Markov chain like structures. Once the pure nondeterminism is resolved, the probalistic behavior of a probalistic automation can be studied. The properties of a randomized algorithm are stated in terms of satisfying some other property with a minimal or maximal probability no matter how the nondeterminism is resolved. In stating the properties of an algorithm we also account for the possibility of imposing restrictions on the ways in which the the nondeterminism is resolved (e.g., fair scheduling, oblivious scheduling,...). We develop techniques to prove the correctness of some property by reducing the problem to the verification of properties of non-randomized systems. One technique is based on coin lemmas, which state the lower bounds on the probability that some chosen random draws give some chosen outcomes no matter how the nondeterminism is resolved. We identify a collection of progress statements which can be used to prove upper bounds to the expected running time of an algorithm. The methods are applied to prove that the randomized dining philosophers algorithm of Lehmann and Rabin guarantees progress in expected constant time and that the randomized algorithm for agreement of Ben-Or guarantees agreement in expected exponential time. To ensure that our new model has strong mathematical foundations, we extend some of the common semantics for labeled transitions systems to the probalistic framework. We define a compositional trace semantic

Modeling and verification of randomized distributed real-time systems

Hybrid systems are systems that exhibit a combination of discrete and continuous behavior. Typical hybrid systems include computer components, which operate in discrete program steps, and real-world components, whose behavior over time intervals evolves according to physical constraints. Important examples of hybrid systems include automated transportation systems, robotics systems, process control systems, systems of embedded devices, and mobile computing systems. Such systems can be very complex, and very difficult to describe and analyze. This paper presents the Hybrid Input/Output Automaton (HIOA) modeling framework, a basic mathematical framework to support description and analysis of hybrid systems. An important feature of this model is its support for decomposing hybrid system descriptions. In particular, the framework includes a notion of external behavior for a hybrid I/O automaton, which captures its discrete and continuous interactions with its environment. The framework also defines what it means for one HIOA to implement another, based on an inclusion relationship between their external behavior sets, and defines a notion of simulation, which provides a sufficient condition for demonstrating implementation relationships. The framework also includes a composition operation for HIOAs, which respects the implementation relation and a notion of receptiveness, which implies that an HIOA does not block the passage of time. The framework is intended to support analysis methods from both computer science and control theory. This work is a simplification of our earlier HIOA model. The main simplification in the new model is a clearer separation between the mechanisms used to model discrete and continuous interaction between components. In particular, the new model removes the dual use of external variables for discrete and continuous interactions.

Hybrid I/O automata

http://qav.comlab.ox.ac.uk/papers/tcs02.pdf

Automatic verification of real-time systems with discrete probability distributions

We propose a new hybrid I/O automaton model that is capable of describing both continuous and discrete behavior. The model, which extends the timed I/O automaton model of [12, 7] and the phase transition system models of [15, 2], allows communication among components using both shared variables and shared actions. The main contributions of this paper are: (1) the definition of hybrid I/O automata and of an implementation relation based on hybrid traces, (2) the definition of a simulation between hybrid I/O automata and a proof that existence of a simulation implies the implementation relation, (3) a definition of composition of hybrid I/O automata and a proof that it respects the implementation relation, and (4) a definition of receptiveness for hybrid I/O automata and a proof that, assuming certain compatibility conditions, receptiveness is preserved by composition.

Roberto Segala

Papers

Probabilistic simulations for probabilistic processes

Modeling and verification of randomized distributed real-time systems

Hybrid I/O automata

Automatic verification of real-time systems with discrete probability distributions

Hybrid I/O automata