Correctness Witness Validation by Abstract Interpretation

Witnesses record automated program analysis results and make them exchangeable. To validate correctness witnesses through abstract interpretation, we introduce a novel abstract operation unassume. This operator incorporates witness invariants into the abstract program state. Given suitable invariants, the unassume operation can accelerate fixpoint convergence and yield more precise results. We demonstrate the feasibility of this approach by augmenting an abstract interpreter with unassume operators and evaluating the impact of incorporating witnesses on performance and precision. Using manually crafted witnesses, we can confirm verification results for multi-threaded programs with a reduction in effort ranging from 7% to 47% in CPU time. More intriguingly, we discover that using witnesses from model checkers can guide our analyzer to verify program properties that it could not verify on its own.Comment: 29 pages, 4 figures, 2 tables, extended version of the paper which is to appear at VMCAI 202

The JKind Model Checker

JKind is an open-source industrial model checker developed by Rockwell Collins and the University of Minnesota. JKind uses multiple parallel engines to prove or falsify safety properties of infinite state models. It is portable, easy to install, performance competitive with other state-of-the-art model checkers, and has features designed to improve the results presented to users: inductive validity cores for proofs and counterexample smoothing for test-case generation. It serves as the back-end for various industrial applications.Comment: CAV 201

Verification Witnesses

Over the last years, witness-based validation of verification results has become an established practice in software verification: An independent validator re-establishes verification results of a software verifier using verification witnesses, which are stored in a standardized exchange format. In addition to validation, such exchangable information about proofs and alarms found by a verifier can be shared across verification tools, and users can apply independent third-party tools to visualize and explore witnesses to help them comprehend the causes of bugs or the reasons why a given program is correct. To achieve the goal of making verification results more accessible to engineers, it is necessary to consider witnesses as first-class exchangeable objects, stored independently from the source code and checked independently from the verifier that produced them, respecting the important principle of separation of concerns. We present the conceptual principles of verification witnesses, give a description of how to use them, provide a technical specification of the exchange format for witnesses, and perform an extensive experimental study on the application of witness-based result validation, using the validators CPAchecker, UAutomizer, CPA-witness2test, and FShell-witness2test

Witness-based validation of verification results with applications to software-model checking

In the scientific world, formal verification is an established engineering technique to ensure the correctness of hardware and software systems. Because formal verification is an arduous and error-prone endeavor, automated solutions are desirable, and researchers continue to develop new algorithms and optimize existing ones to push the boundaries of what can be verified automatically. These efforts do not go unnoticed by the industry. Hardware-circuit designs, flight-control systems, and operating-system drivers are just a few examples of systems where formal verification is already part of the quality-assurance repertoire. Nevertheless, the primary fields of application for formal verification are mainly those where errors carry a high risk of significant damage, either financial or physical, because the costs of formal verification are considered to be too high for most other projects, despite the fact that the research community has made vast advancements regarding the effectiveness and efficiency of formal verification techniques in the last decades. We present and address two potential reasons for this discrepancy that we identified in the field of automated formal software verification. (1) Even for experts in the field, it is often difficult to decide which of the multitude of available techniques is the most suitable solution they should recommend to solve a given verification problem. Moreover, even if a suitable solution is found for a given system, there is no guarantee that the solution is sustainable as the system evolves. Consequently, the cost of finding and maintaining a suitable approach for applying formal software verification to real-world systems is high. (2) Even assuming that a suitable and maintainable solution for applying formal software verification to a given system is found and verification results could be obtained, developers of the system still require further guidance towards making practical use of these results, which often differ significantly from the results they obtain from classical quality-assurance techniques they are familiar with, such as testing. To mitigate the first issue, using the open-source software-verification framework CPAchecker, we investigate several popular formal software-verification techniques such as predicate abstraction, Impact, bounded model checking, k -induction, and PDR, and perform an extensive and rigorous experimental study to identify their strengths and weaknesses regarding their comparative effectiveness and efficiency when applied to a large and established benchmark set, to provide a basis for choosing the best technique for a given problem. To mitigate the second issue, we propose a concrete standard format for the representation and communication of verification results that raises the bar from plain "yes" or "no" answers to verification witnesses, which are valuable artifacts of the verification process that contain detailed information discovered during the analysis. We then use these verification witnesses for several applications: To increase the trust in verification results, we irst develop several independent validators based on violation witnesses, i.e. verification witnesses that represent bugs detected by a verifier. We then extend our validators to also erify the verification results obtained from a successful verification, which are represented y correctness witnesses. Lastly, we also develop an interactive web service to store and retrieve these verification witnesses, to provide online validation to quickly de-prioritize likely wrong results, and to graphically visualize the witnesses, as an example of how verification can be integrated into a development process. Since the introduction of our proposed standard format for verification witnesses, it has been adopted by over thirty different software verifiers, and our witness-based result-validation tools have become a core component in the scoring process of the International Competition on Software Verification.In der Welt der Wissenschaft gilt die Formale Verifikation als etablierte Methode, die Korrektheit von Hard- und Software zu gewährleisten. Da die Anwendung formaler Verifikation jedoch selbst ein beschwerliches und fehlerträchtiges Unterfangen darstellt, ist es erstrebenswert, automatisierte Lösungen dafür zu finden. Forscher entwickeln daher immer wieder neue Algorithmen Formaler Verifikation oder verbessern bereits existierende Algorithmen, um die Grenzen der Automatisierbarkeit Formaler Verifikation weiter und weiter zu dehnen. Auch die Industrie ist bereits auf diese Anstrengungen aufmerksam geworden. Flugsteuerungssysteme, Betriebssystemtreiber und Entwürfe von Hardware-Schaltungen sind nur einzelne Beispiele von Systemen, bei denen Formale Verifikation bereits heute einen festen Stammplatz im Arsenal der Qualitätssicherungsmaßnahmen eingenommen hat. Trotz alledem bleiben die primären Einsatzgebiete Formaler Verifikation jene, in denen Fehler ein hohes Risiko finanzieller oder physischer Schäden bergen, da in anderen Projekten die Kosten des Einsatzes Formaler Verifikation in der Regel als zu hoch empfunden werden, unbeachtet der Tatsache, dass es der Forschungsgemeinschaft in den letzten Jahrzehnten gelungen ist, enorme Fortschritte bei der Verbesserung der Effektivität und Effizienz Formaler Verifikationstechniken zu machen. Wir präsentieren und diskutieren zwei potenzielle Ursachen für diese Diskrepanz zwischen Forschung und Industrie, die wir auf dem Gebiet der Automatisierten Formalen Softwareverifikation identifiziert haben. (1) Sogar Fachleuten fällt es oft schwer, zu entscheiden, welche der zahlreichen verfügbaren Methoden sie als vielversprechendste Lösung eines gegebenen Verifikationsproblems empfehlen sollten. Darüber hinaus gibt es selbst dann, wenn eine passende Lösung für ein gegebenes System gefunden wird, keine Garantie, dass sich diese Lösung im Laufe der Evolution des Systems als Nachhaltig erweisen wird. Daher sind sowohl die Wahl als auch der Unterhalt eines passenden Ansatzes zur Anwendung Formaler Softwareverifikation auf reale Systeme kostspielige Unterfangen. (2) Selbst unter der Annahme, dass eine passende und wartbare Lösung zur Anwendung Formaler Softwareverifikation auf ein gegebenes System gefunden und Verifikationsergebnisse erzielt werden, benötigen die Entwickler des Systems immer noch weitere Unterstützung, um einen praktischen Nutzen aus den Ergebnissen ziehen zu können, die sich oft maßgeblich unterscheiden von den Ergebnissen jener klassischen Qualitätssicherungssysteme, mit denen sie vertraut sind, wie beispielsweise dem Testen. Um das erste Problem zu entschärfen, untersuchen wir unter Verwendung des Open-Source-Softwareverifikationsystems CPAchecker mehrere beliebte Formale Softwareverifikationsmethoden, wie beispielsweise Prädikatenabstraktion, Impact, Bounded-Model-Checking, k-Induktion und PDR, und führen umfangreiche und gründliche experimentelle Studien auf einem großen und etablierten Konvolut an Beispielprogrammen durch, um die Stärken und Schwächen dieser Methoden hinsichtlich ihrer relativen Effektivität und Effizienz zu ermitteln und daraus eine Entscheidungsgrundlage für die Wahl der besten Lösung für ein gegebenes Problem abzuleiten. Um das zweite Problem zu entschärfen, schlagen wir ein konkretes Standardformat zur Modellierung und zum Austausch von Verifikationsergebnissen vor, welches die Ansprüche an Verifikationsergebnisse anhebt, weg von einfachen "ja/nein"-Antworten und hin zu Verifikationszeugen (Verification Witnesses), bei denen es sich um wertvolle Produkte des Verifikationsprozesses handelt und die detaillierte, während der Analyse entdeckte Informationen enthalten. Wir stellen mehrere Anwendungsbeispiele für diese Verifikationszeugen vor: Um das Vertrauen in Verifikationsergebnisse zu erhöhen, entwickeln wir zunächst mehrere, voneinander unabhängige Validatoren, die Verletzungszeugen (Violation Witnesses) verwenden, also Verifikationszeugen, welche von einem Verifikationswerkzeug gefundene Spezifikationsverletzungen darstellen, Diese Validatoren erweitern wir anschließend so, dass sie auch in der Lage sind, die Verifikationsergebnisse erfolgreicher Verifikationen, also Korrektheitsbehauptungen, die durch Korrektheitszeugen (Correctness Witnesses) dokumentiert werden, nachzuvollziehen. Schlussendlich entwickeln wir als Beispiel für die Integrierbarkeit Formaler Verifikation in den Entwicklungsprozess einen interaktiven Webservice für die Speicherung und den Abruf von Verifikationzeugen, um einen Online-Validierungsdienst zur schnellen Depriorisierung mutmaßlich falscher Verifikationsergebnisse anzubieten und Verifikationszeugen graphisch darzustellen. Unser Vorschlag für ein Standardformat für Verifikationszeugen wurde inzwischen von mehr als dreißig verschiedenen Softwareverifikationswerkzeugen übernommen und unsere zeugen-basierten Validierungswerkzeuge sind zu einer Kernkomponente des Bewertungsschemas des Internationalen Softwareverifikationswettbewerbs geworden

B-FERL: Blockchain based Framework for Securing Smart Vehicles

The ubiquity of connecting technologies in smart vehicles and the incremental automation of its functionalities promise significant benefits, including a significant decline in congestion and road fatalities. However, increasing automation and connectedness broadens the attack surface and heightens the likelihood of a malicious entity successfully executing an attack. In this paper, we propose a Blockchain based Framework for sEcuring smaRt vehicLes (B-FERL). B-FERL uses permissioned blockchain technology to tailor information access to restricted entities in the connected vehicle ecosystem. It also uses a challenge-response data exchange between the vehicles and roadside units to monitor the internal state of the vehicle to identify cases of in-vehicle network compromise. In order to enable authentic and valid communication in the vehicular network, only vehicles with a verifiable record in the blockchain can exchange messages. Through qualitative arguments, we show that B-FERL is resilient to identified attacks. Also, quantitative evaluations in an emulated scenario show that B-FERL ensures a suitable response time and required storage size compatible with realistic scenarios. Finally, we demonstrate how B-FERL achieves various important functions relevant to the automotive ecosystem such as trust management, vehicular forensics and secure vehicular networks.Comment: 11 Pages, 8 Figure

Incorporating Data Dependencies and Properties in Difference Verification with Conditions (Technical Report)

Software changes frequently. To efficiently deal with such frequent changes, software verification tools must be incremental. Most of today's approaches for incremental verification consider one specific verification approach. One exception is difference verification with conditions recently proposed by Beyer et al. Its underlying idea is to determine an overapproximation of those modified execution paths that may cause a new property violation, which does not exist in the unchanged program, encode the determined paths into a condition, and use the condition to restrict the verification to the analysis of those determined paths. To determine the overapproximation, Beyer et al. propose a syntax-based difference detector that adds any syntactical path of the modified program that does not exist in the original program into the overapproximation. This paper provides a second difference detector diffDP, which computes a more precise overapproximation by taking data dependencies and program properties into account when determining the overapproximation of those modified execution paths that may cause a new property violation. Our evaluation indeed shows that our more precise difference detector improves the effectiveness and efficiency of difference verification with condition on several tasks

Privacy-preserving and accountable on-the-road prosecution of invalid vehicular mandatory authorizations

Nowadays, improving road safety is one of the major challenges in developed countries and, to this regard, attaining more effectiveness in the enforcement of road safety policies has become a key target. In particular, enforcing the requirements related to the technical and administrative mandatory documentation of on-the-road motor vehicles is one of the critical issues. The use of modern technologies in the context of Intelligent Transportation Systems (ITS) could enable the design of a more convenient, frequent and effective enforcement system compared to the traditional human patrol controls. In this article we propose a novel system for the on-the-fly verification of mandatory technical and administrative documentation of motor vehicles. Vehicles not complying with the required regulations will be identified and sanctioned whereas those vehicles, observant of the mandatory regulations, will maintain anonymity and non-traceability of their whereabouts. The proposed system is based on the use of anonymous credentials which will be loaded onto the vehicle to automatically and on-the-fly prove holdership of required credentials without requiring the vehicle to stop beside the road. We also implement a prototype of the credential system and analyze the feasibility of our solution in terms of computational cost and time to perform such telematic controls.This work has been funded by grant CCG10-UC3M/TIC-5174 (project PRECIOUS) and partially by grant TIN2009-13461 (project E-SAVE).En prens