Verification Of Distributed Systems Research Articles

AdoB: Bridging Benign and Byzantine Consensus with Atomic Distributed Objects

Achieving consensus is a challenging and ubiquitous problem in distributed systems that is only made harder by the introduction of malicious byzantine servers. While significant effort has been devoted to the benign and byzantine failure models individually, no prior work has considered the mechanized verification of both in a generic way. We claim this is due to the lack of an appropriate abstraction that is capable of representing both benign and byzantine consensus without either losing too much detail or becoming impractically complex. We build on recent work on the atomic distributed object model to fill this void with a novel abstraction called AdoB. In addition to revealing important insights into the essence of consensus, this abstraction has practical benefits for easing distributed system verification. As a case study, we proved safety and liveness properties for AdoB in Coq, which are the first such mechanized proofs to handle benign and byzantine consensus in a unified manner. We also demonstrate that AdoB faithfully models real consensus protocols by proving it is refined by standard network-level specifications of Fast Paxos and a variant of Jolteon.

Message Chains for Distributed System Verification

Message Chains for Distributed System Verification

Coq에서의 실시간 분산 시스템 검증을 위한 네트워크 및 운영체제 행동의 정형 모델 정의

정형 검증을 적용하여 분산 시스템의 안전성을 높이는 것은 중요한 과제이다. 분산 시스템 중 항공, 의료기기와 같은 안전 우선 시스템은 안전성의 위협이 큰 사고와 직결될 수 있다. 하지만 분산 시스템을 정형 검증하기 위해서는 소프트웨어의 실행 의미뿐만 아니라, 소프트웨어를 실행시키는 운영체제와 메시지를 전달하는 네트워크의 환경 등에 대한 기술이 필요하다. 우리는 Coq 증명 보조 도구 안에서 네트워크와 운영체제의 추상적인 행동에 대한 모델을 정의하였다. 이 모델은 단계적으로 네트워크 각 지역의 실행 규칙을 제시하고, 이로부터 전체 시스템의 행동을 구성한다. 우리는 이 모델이 실제로 분산 시스템 검증에 유용하게 사용될 수 있음을 보이기 위해 간단한 서버-클라이언트 시스템 검증을 수행하였으며, 이후 실용적인 소프트웨어 검증에 적용되기를 기대하고 있다.

Igloo: soundly linking compositional refinement and separation logic for distributed system verification

Lighthouse projects like CompCert, seL4, IronFleet, and DeepSpec have demonstrated that full system verification is feasible by establishing a refinement between an abstract system specification and an executable implementation. Existing approaches however impose severe restrictions on the abstract system specifications due to their limited expressiveness or versatility, or on the executable code due to their use of suboptimal code extraction or inexpressive program logics. We propose a novel methodology that combines the compositional refinement of event-based models of distributed systems with the verification of full-fledged program code using expressive separation logics, which support features of realistic programming languages like heap data structures and concurrency. Our main technical contribution is a formal framework that soundly relates event-based system models to program specifications in separation logics. This enables protocol development tools to soundly interoperate with program verifiers to establish a refinement between the model and the code. We formalized our framework, Igloo, in Isabelle/HOL. We report on three case studies, a leader election protocol, a replication protocol, and a security protocol, for which we refine formal requirements into program specifications that we implement in Java and Python and prove correct using the VeriFast and Nagini tools.

Formal verification of distributed system using an executable C model

Formal verification means to rigorously explore the correctness of system designs expressed as mathematical models, most likely with the assistance of modern computers. Original approaches were to model and express a distributed system using existing theoretical tools such as Petri Nets. Nevertheless the main problems of such approaches are the restrictions imposed by formal tools and the human factor of simplify and model a distributed system. We propose a way to do formal verification of a distributed system by modeling the communication of the system as a concurrent program, instantiating the distributed system using threads and atomic queues and testing/verifying directly to the source code with specialized verifiers for concurrent programs. As an example, we show the verification of a distributed threshold signer using CBMC verifying properties such as memory leaks, index out of bounds, and data races.

Teaching Formal Models of Concurrency Specification and Analysis

There is a widespread and rapidly growing interest to the parallel programming nowadays. This interest is based on availability of supercomputers, computer clusters and powerful graphic processors for computational mathematics and simulation. MPI, OpenMP, CUDA and other technologies provide opportunity to write C and FORTRAN code for parallel speed-up of execution without races for resources. Nevertheless concurrency issues (like races) are still very important for parallel systems in general and distributed systems in particular. Due to this reason, there is a need of research, study and teaching of formal models of concurrency and methods of distributed system verification. The paper presents an individual experience with teaching Formal Models of Concurrency as a graduate elective course for students specializing in high-performance computing. First it sketches course background, objectives, lecture plan and topics. Then the paper presents how to formalize (i.e. specify) a reachability puzzle in semantic, syntactic and logic formal models, namely: in Petri nets, in a dialect of Calculus of Communicating Systems (CCS) and in Computation Tree Logic (CTL). This puzzle is a good educational example to present specifics of different formal notations. The article is published in the author’s wording.

Space station data management system: A common GSE test interface for systems testing and verification

This paper examines the fundamental problems and goals associated with test, verification, and flight-certification of man-rated distributed data systems. First, a summary of the characteristics of modern computer systems that affect the testing process is provided. Then, verification requirements are expressed in terms of an overall test philosophy for distributed computer systems. This test philosophy stems from previous experience that was gained with centralized systems (Apollo and the Space Shuttle), and deals directly with the new problems that verification of distributed systems may present. Finally, a description of potential hardware and software tools to help solve these problems is provided.