Possibilistic Information Flow Control for Workflow Management Systems

In workflows and business processes, there are often security requirements on both the data, i.e. confidentiality and integrity, and the process, e.g. separation of duty. Graphical notations exist for specifying both workflows and associated security requirements. We present an approach for formally verifying that a workflow satisfies such security requirements. For this purpose, we define the semantics of a workflow as a state-event system and formalise security properties in a trace-based way, i.e. on an abstract level without depending on details of enforcement mechanisms such as Role-Based Access Control (RBAC). This formal model then allows us to build upon well-known verification techniques for information flow control. We describe how a compositional verification methodology for possibilistic information flow can be adapted to verify that a specification of a distributed workflow management system satisfies security requirements on both data and processes.Comment: In Proceedings GraMSec 2014, arXiv:1404.163

Composition and Declassification in Possibilistic Information Flow Security

Formal methods for security can rule out whole classes of security vulnerabilities, but applying them in practice remains challenging. This thesis develops formal verification techniques for information flow security that combine the expressivity and scalability strengths of existing frameworks. It builds upon Bounded Deducibility (BD) Security, which allows specifying and verifying fine-grained policies about what information may flow when to whom. Our main technical result is a compositionality theorem for BD Security, providing scalability by allowing us to verify security properties of a large system by verifying smaller components. Its practical utility is illustrated by a case study of verifying confidentiality properties of a distributed social media platform. Moreover, we discuss its use for the modular development of secure workflow systems, and for the security-preserving enforcement of safety and security properties other than information flow control

Aspects Of Knowledge And Belief-Based Programming

It has long been recognized that many distributed problems can be analyzed in terms of how agents act based on what they know about the system they are in. To make this intuition formal, Fagin, Halpern, Moses, and Vardi [25, 26] proposed a theory of programs for multi-agent systems in which preconditions of actions are formulas in a logic of knowledge. Knowledge-based programs have been successfully applied to a number of fundamental problems. This dissertation aims at further investigating the role of knowledge-based programs in the study of distributed systems. We focus ?rst on a general problem in distributed settings: given a function f whose value depends on the whole network N , the goal is for every agent to eventually compute the value f (N ). We call this problem global function computation. We give a necessary and suf?cient condition for the problem to be solvable and provide a knowledge-based program that solves the global function computation problem whenever possible. The program guarantees a certain level of optimality by having agents send messages only when they believe it is necessary to do so, and allows for systems in which agents are anonymous. Second, we consider the synthesis of knowledge-based programs. In general, to produce a program guaranteed to satisfy a given speci?cation, one can try to synthesize it from a formal proof that a computation satisfying that speci?cation exists. We build on a technique proposed by Bickford and Constable [11, 12] for extracting message automata from speci?cations of multi-agent systems to show how knowledge-based message automata can be synthesized using a proof development system such as Nuprl [19]. Third, we consider the problem of ensuring secrecy in a multi-agent system by disallowing unwanted ?ows of information. We discuss knowledge-based formulations of information-?ow properties, with a focus on the basic security predicates in the Modular Assembly Kit proposed by Mantel [62]

CoSMeDis : a distributed social media platform with formally verified confidentiality guarantees

We present the design, implementation and information flow verification of CoSMeDis, a distributed social media platform. The system consists of an arbitrary number of communicating nodes, deployable at different locations over the Internet. Its registered users can post content and establish intra-node and inter-node friendships, used to regulate access control over the posts. The system's kernel has been verified in the proof assistant Isabelle/HOL and automatically extracted as Scala code. We formalized a framework for composing a class of information flow security guarantees in a distributed system, applicable to input/output automata. We instantiated this framework to confidentiality properties for CoSMeDis's sources of information: posts, friendship requests, and friendship status

CoSMeDis: a distributed social media platform with formally verified confidentiality guarantees

We present the design, implementation and information flow verification of CoSMeDis, a distributed social media platform. The system consists of an arbitrary number of communicating nodes, deployable at different locations over the Internet. Its registered users can post content and establish intra-node and inter-node friendships, used to regulate access control over the posts. The system’s kernel has been verified in the proof assistant Isabelle/HOL and automatically extracted as Scala code. We formalized a framework for composing a class of information flow security guarantees in a distributed system, applicable to input/output automata. We instantiated this framework to confidentiality properties for CoSMeDis’s sources of information: posts, friendship requests, and friendship status

Belief change operations under confidentiality requirements in multiagent systems

Multiagent systems are populated with autonomous computing entities called agents which pro-actively pursue their goals. The design of such systems is an active field within artificial intelligence research with one objective being flexible and adaptive agents in dynamic and inaccessible environments. An agent's decision-making and finally its success in achieving its goals crucially depends on the agent's information about its environment and the sharing of information with other agents in the multiagent system. For this and other reasons, an agent's information is a valuable asset and thus the agent is often interested in the confidentiality of parts of this information. From research in computer security it is well-known that confidentiality is not only achieved by the agent's control of access to its data, but by its control of the flow of information when processing the data during the interaction with other agents. This thesis investigates how to specify and enforce the confidentiality interests of an agent D while it reacts to iterated query, revision and update requests from another agent A for the purpose of information sharing. First, we will enable the agent D to specify in a dedicated confidentiality policy that parts of its previous or current belief about its environment should be hidden from the other requesting agent A. To formalize the requirement of hiding belief, we will in particular postulate agent A's capabilities for reasoning about D's belief and about D's processing of information to form its belief. Then, we will relate the requirements imposed by a confidentiality policy to others in the research of information flow control and inference control in computer security. Second, we will enable the agent D to enforce its confidentiality aims as expressed by its policy by refusing requests from A at a potential violation of its policy. A crucial part of the enforcement is D's simulation of A's postulated reasoning about D's belief and the change of this belief. In this thesis, we consider two particular operators of belief change: an update operator for a simple logic-oriented database model and a revision operator for D's assertions about its environment that yield the agent's belief after its nonmonotonic reasoning. To prove the effectiveness of D's means of enforcement, we study necessary properties of D's simulation of A and then based on these properties show that D's enforcement is effective according to the formal requirements of its policy

A temporal logic approach to information-flow control

Information leaks and other violations of information security pose a severe threat to individuals, companies, and even countries. The mechanisms by which attackers threaten information security are diverse and to show their absence thus proved to be a challenging problem. Information-flow control is a principled approach to prevent security incidents in programs and other technical systems. In information-flow control we define information-flow properties, which are sufficient conditions for when the system is secure in a particular attack scenario. By defining the information-flow property only based on what parts of the executions of the system a potential attacker can observe or control, we obtain security guarantees that are independent of implementation details and thus easy to understand. There are several methods available to enforce (or verify) information-flow properties once defined. We focus on static enforcement methods, which automatically determine whether a given system satisfies a given information-flow property for all possible inputs to the system. Most enforcement approaches that are available today have one problem in common: they each only work for one particular programming language or information-flow property. In this thesis, we propose a temporal logic approach to information-flow control to provide a simple formal basis for the specification and enforcement of information-flow properties. We show that the approach can be used to enforce a wide range of information-flow properties with a single algorithm. The main challenge is that the standard temporal logics are unable to express information-flow properties. They lack the ability to relate multiple executions of a system, which is essential for information-flow properties. We thus extend the temporal logics LTL and CTL* by the ability to quantify over multiple executions and to relate them using boolean and temporal operators. The resulting temporal logics HyperLTL and HyperCTL* can express many information-flow properties of interest. The extension of temporal logics com- pels us to revisit the algorithmic problem to check whether a given system (model) satisfies a given specification in HyperLTL or HyperCTL*; also called the model checking problem. On the technical side, the main contribution is a model checking algorithm for HyperLTL and HyperCTL* and the detailed complexity analysis of the model checking problem: We give nonelementary lower and upper bounds for its computational complexity, both in the size of the system and the size of the specification. The complexity analysis also reveals a class of specification, which includes many of the commonly consid- ered information-flow properties and for which the algorithm is efficient (in NLOGSPACE in the size of the system). For this class of efficiently checkable properties, we provide an approach to reuse existing technology in hardware model checking for information-flow control. We demonstrate along a case study that the temporal logic approach to information-flow control is flexible and effective. We further provide two case studies that demonstrate the use of HyperLTL and HyperCTL* for proving properties of error resistant codes and distributed protocols that have so far only been considered in manual proofs.Informationssicherheit stellt eine immer größere Bedrohung für einzelne Personen, Firmen und selbst ganze Länder dar. Ein grundlegender Ansatz zur Vorbeugung von Sicherheitsproblemen in technischen Systemen, wie zum Beispiel Programmen, ist Informationsflusskontrolle. In der Informationsflusskontrolle definieren wir zunächst sogenannte Informationsflusseigenschaften, welche hinreichende Bedingungen für die Sicherheit des gegebenen Systems in einem Sicherheitsszenario darstellen. Indem wir Informationsflusseigenschaften nur auf Basis der möglichen Beobachtungen eines Angreifers über das System definieren, erhalten wir einfach zu verstehende Sicherheitsgarantien, die unabhängig von Implementierungsdetails sind. Nach der Definition von Eigenschaften muss sichergestellt werden, dass ein gegebenes System seine Informationsflusseigenschaft erfüllt, wofür es bereits verschiedene Methoden gibt. Wir fokussieren uns in dieser Arbeit auf statische Methoden, welche für ein gegebenes System und eine gegebene Informationsflusseigenschaft automatisch entscheiden, ob das System die Eigenschaft für alle möglichen Eingaben erfüllt, was wir auch das Modellprüfungsproblem nennen. Die meisten verfügbaren Methoden zum Sicherstellen der Einhaltung von Informationsflusseigenschaften teilen jedoch eine Schwäche: sie funktionieren nur für eine einzelne Programmiersprache oder eine einzelne Informationsflusseigenschaft. In dieser Arbeit verfolgen wir einen Ansatz basierend auf Temporallogiken, um eine einfache theoretische Basis für die Spezifikation von Informationsflusseigenschaften und deren Umsetzung zu erhalten. Wir analysieren den Zusammenhang von der Ausdrucksmächtigkeit von Spezifikationssprachen und dem algorithmischen Problem Spezifikationen für ein System zu überprüfen. Anhand einer Fallstudie im Bereich der Hardwaresicherheit zeigen wir, dass der Ansatz dazu geeignet ist eine breite Palette von bekannten und neuen Informationsflusseigenschaften mittels eines einzelnen Modellprüfungsalgorithmus zu beweisen. Das Kernproblem hierbei ist, dass wir in den üblichen Temporallogiken Informationsflusseigenschaften nicht ausdrücken können, es fehlt die Fähigkeit mehrere Ausführungen eines Systems miteinander zu vergleichen, was der gemeinsame Nenner von Informationsflusseigenschaften ist. Wir erweitern Temporallogiken daher um die Fähigkeit über mehrere Ausführungen zu quantifizieren und diese miteinander zu vergleichen. Der Hauptbeitrag auf der technischen Ebene ist ein Modellprüfungsalgorithmus und eine detaillierte Analyse der Komplexität des Modellprüfungsproblems. Wir geben einen Modellprüfungsalgorithmus an und beweisen, dass der Algorithmus asymptotisch optimal ist. Die Komplexitätsanalyse zeigt auch eine Klasse von Eigenschaften auf, welche viele der üblichen Informationsflusseigenschaften beinhaltet, und für welche der gegebene Algorithmus effizient ist (in NLOGSPACE in der Größe des Systems). Für diese Klasse von effizient überprüfbaren Eigenschaften diskutieren wir einen Ansatz bestehende Technologie zur Modellprüfung von Hardware für Informationsflusskontrolle wiederzuverwenden. Anhand einer Fallstudie zeigen wir, dass der Ansatz flexibel und effektiv eingesetzt werden kann. Desweiteren diskutieren wir zwei weitere Fallstudien, welche demonstrieren, dass die vorgeschlagene Erweiterung von Temporallogiken auch eingesetzt werden kann, um Eigenschaften für fehlerresistente Kodierungen und verteilte Protokolle zu beweisen, welche bisher nur Abstrakt betrachtet werden konnten

A temporal logic approach to information-flow control

Information leaks and other violations of information security pose a severe threat to individuals, companies, and even countries. The mechanisms by which attackers threaten information security are diverse and to show their absence thus proved to be a challenging problem. Information-flow control is a principled approach to prevent security incidents in programs and other technical systems. In information-flow control we define information-flow properties, which are sufficient conditions for when the system is secure in a particular attack scenario. By defining the information-flow property only based on what parts of the executions of the system a potential attacker can observe or control, we obtain security guarantees that are independent of implementation details and thus easy to understand. There are several methods available to enforce (or verify) information-flow properties once defined. We focus on static enforcement methods, which automatically determine whether a given system satisfies a given information-flow property for all possible inputs to the system. Most enforcement approaches that are available today have one problem in common: they each only work for one particular programming language or information-flow property. In this thesis, we propose a temporal logic approach to information-flow control to provide a simple formal basis for the specification and enforcement of information-flow properties. We show that the approach can be used to enforce a wide range of information-flow properties with a single algorithm. The main challenge is that the standard temporal logics are unable to express information-flow properties. They lack the ability to relate multiple executions of a system, which is essential for information-flow properties. We thus extend the temporal logics LTL and CTL* by the ability to quantify over multiple executions and to relate them using boolean and temporal operators. The resulting temporal logics HyperLTL and HyperCTL* can express many information-flow properties of interest. The extension of temporal logics com- pels us to revisit the algorithmic problem to check whether a given system (model) satisfies a given specification in HyperLTL or HyperCTL*; also called the model checking problem. On the technical side, the main contribution is a model checking algorithm for HyperLTL and HyperCTL* and the detailed complexity analysis of the model checking problem: We give nonelementary lower and upper bounds for its computational complexity, both in the size of the system and the size of the specification. The complexity analysis also reveals a class of specification, which includes many of the commonly consid- ered information-flow properties and for which the algorithm is efficient (in NLOGSPACE in the size of the system). For this class of efficiently checkable properties, we provide an approach to reuse existing technology in hardware model checking for information-flow control. We demonstrate along a case study that the temporal logic approach to information-flow control is flexible and effective. We further provide two case studies that demonstrate the use of HyperLTL and HyperCTL* for proving properties of error resistant codes and distributed protocols that have so far only been considered in manual proofs.Informationssicherheit stellt eine immer größere Bedrohung für einzelne Personen, Firmen und selbst ganze Länder dar. Ein grundlegender Ansatz zur Vorbeugung von Sicherheitsproblemen in technischen Systemen, wie zum Beispiel Programmen, ist Informationsflusskontrolle. In der Informationsflusskontrolle definieren wir zunächst sogenannte Informationsflusseigenschaften, welche hinreichende Bedingungen für die Sicherheit des gegebenen Systems in einem Sicherheitsszenario darstellen. Indem wir Informationsflusseigenschaften nur auf Basis der möglichen Beobachtungen eines Angreifers über das System definieren, erhalten wir einfach zu verstehende Sicherheitsgarantien, die unabhängig von Implementierungsdetails sind. Nach der Definition von Eigenschaften muss sichergestellt werden, dass ein gegebenes System seine Informationsflusseigenschaft erfüllt, wofür es bereits verschiedene Methoden gibt. Wir fokussieren uns in dieser Arbeit auf statische Methoden, welche für ein gegebenes System und eine gegebene Informationsflusseigenschaft automatisch entscheiden, ob das System die Eigenschaft für alle möglichen Eingaben erfüllt, was wir auch das Modellprüfungsproblem nennen. Die meisten verfügbaren Methoden zum Sicherstellen der Einhaltung von Informationsflusseigenschaften teilen jedoch eine Schwäche: sie funktionieren nur für eine einzelne Programmiersprache oder eine einzelne Informationsflusseigenschaft. In dieser Arbeit verfolgen wir einen Ansatz basierend auf Temporallogiken, um eine einfache theoretische Basis für die Spezifikation von Informationsflusseigenschaften und deren Umsetzung zu erhalten. Wir analysieren den Zusammenhang von der Ausdrucksmächtigkeit von Spezifikationssprachen und dem algorithmischen Problem Spezifikationen für ein System zu überprüfen. Anhand einer Fallstudie im Bereich der Hardwaresicherheit zeigen wir, dass der Ansatz dazu geeignet ist eine breite Palette von bekannten und neuen Informationsflusseigenschaften mittels eines einzelnen Modellprüfungsalgorithmus zu beweisen. Das Kernproblem hierbei ist, dass wir in den üblichen Temporallogiken Informationsflusseigenschaften nicht ausdrücken können, es fehlt die Fähigkeit mehrere Ausführungen eines Systems miteinander zu vergleichen, was der gemeinsame Nenner von Informationsflusseigenschaften ist. Wir erweitern Temporallogiken daher um die Fähigkeit über mehrere Ausführungen zu quantifizieren und diese miteinander zu vergleichen. Der Hauptbeitrag auf der technischen Ebene ist ein Modellprüfungsalgorithmus und eine detaillierte Analyse der Komplexität des Modellprüfungsproblems. Wir geben einen Modellprüfungsalgorithmus an und beweisen, dass der Algorithmus asymptotisch optimal ist. Die Komplexitätsanalyse zeigt auch eine Klasse von Eigenschaften auf, welche viele der üblichen Informationsflusseigenschaften beinhaltet, und für welche der gegebene Algorithmus effizient ist (in NLOGSPACE in der Größe des Systems). Für diese Klasse von effizient überprüfbaren Eigenschaften diskutieren wir einen Ansatz bestehende Technologie zur Modellprüfung von Hardware für Informationsflusskontrolle wiederzuverwenden. Anhand einer Fallstudie zeigen wir, dass der Ansatz flexibel und effektiv eingesetzt werden kann. Desweiteren diskutieren wir zwei weitere Fallstudien, welche demonstrieren, dass die vorgeschlagene Erweiterung von Temporallogiken auch eingesetzt werden kann, um Eigenschaften für fehlerresistente Kodierungen und verteilte Protokolle zu beweisen, welche bisher nur Abstrakt betrachtet werden konnten

Untangling hotel industry’s inefficiency: An SFA approach applied to a renowned Portuguese hotel chain

The present paper explores the technical efficiency of four hotels from Teixeira Duarte Group - a renowned Portuguese hotel chain. An efficiency ranking is established from these four hotel units located in Portugal using Stochastic Frontier Analysis. This methodology allows to discriminate between measurement error and systematic inefficiencies in the estimation process enabling to investigate the main inefficiency causes. Several suggestions concerning efficiency improvement are undertaken for each hotel studied.info:eu-repo/semantics/publishedVersio

Possibilistic information flow control in MAKS and action refinement

Abstract. Formal methods emphasizes the need for a top-down approach when developing large reliable software systems. Refinements are used to map step by step abstract algebraic specifications to executable specifications. Action refinements are used to add detailed design information to abstract actions. Information flow control is used to specify and verify the admissible flow of confidential information in a complex system. However, it is well-known that in general action refinement will not preserve information flow properties which have been proved on an abstract level. In this paper we develop criteria ensuring that these properties are inherited during action refinement. We adopt Mantel’s MAKS framework on possibilistic information flow control to formulate security predicates but advance to configuration structures instead of trace event systems to cope with necessary modeling of concurrency.