2,567 research outputs found

    Developing theoretical foundations for runtime enforcement

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    The ubiquitous reliance on software systems is increasing the need for ensuring their correctness. Runtime enforcement is a monitoring technique that uses moni- tors that can transform the actions of a system under scrutiny in order to alter its runtime behaviour and keep it in line with a correctness specification; these type of enforcement monitors are often called transducers. In runtime enforcement there is often no clear separation between the specification language describing the cor- rectness criteria that a system must satisfy, and the monitoring mechanism that actually ensures that these criteria are met. We thus aim to adopt a separation of concerns between the correctness specification describing what properties the sys- tem should satisfy, and the monitor describing how to enforce these properties. In this thesis we study the enforceability of the highly expressive branching time logic μHML, in a bid to identify a subset of this logic whose formulas can be adequately enforced by transducers at runtime. We conducted our study in relation to two different enforcement instrumentation settings, namely, a unidirectional setting that is simpler to understand and formalise but limited in the type of system actions it can transform at runtime, and a bidirectional one that, albeit being more complex, it allows transducers to effect and modify a wider set of system actions. During our investigation we define the behaviour of enforcement transducers and how they should be embedded with a system to achieve unidirectional and bidirectional enforcement. We also investigate what it means for a monitor to adequately enforce a logic formula, and define the necessary criteria that a monitor must satisfy in order to be adequate. Since enforcement monitors are highly intrusive, we also define a notion of optimality to use as a guide for identifying the least intrusive monitor that adequately enforces a formula. Using these enforcement definitions, we identify a μHML fragment that can be adequately enforced via enforcement transducers that drop the execution of certain actions. We then show that this fragment is maximally expressive, i.e., it is the largest subset that can be enforced via these type of enforcement monitors. We finally look into static alternatives to runtime enforcement and identify a static analysis technique that can also enforce the identified μHML fragment, but without requiring the system to execute

    Using Event Calculus to Formalise Policy Specification and Analysis

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    As the interest in using policy-based approaches for systems management grows, it is becoming increasingly important to develop methods for performing analysis and refinement of policy specifications. Although this is an area that researchers have devoted some attention to, none of the proposed solutions address the issues of analysing specifications that combine authorisation and management policies; analysing policy specifications that contain constraints on the applicability of the policies; and performing a priori analysis of the specification that will both detect the presence of inconsistencies and explain the situations in which the conflict will occur. We present a method for transforming both policy and system behaviour specifications into a formal notation that is based on event calculus. Additionally it describes how this formalism can be used in conjunction with abductive reasoning techniques to perform a priori analysis of policy specifications for the various conflict types identified in the literature. Finally, it presents some initial thoughts on how this notation and analysis technique could be used to perform policy refinement

    On Runtime Enforcement via Suppressions

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    Runtime enforcement is a dynamic analysis technique that uses monitors to enforce the behaviour specified by some correctness property on an executing system. The enforceability of a logic captures the extent to which the properties expressible via the logic can be enforced at runtime. We study the enforceability of Hennessy-Milner Logic with Recursion (muHML) with respect to suppression enforcement. We develop an operational framework for enforcement which we then use to formalise when a monitor enforces a muHML property. We also show that the safety syntactic fragment of the logic, sHML, is enforceable by providing an automated synthesis function that generates correct suppression monitors from sHML formulas

    CEEME: compensating events based execution monitoring enforcement for Cyber-Physical Systems

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    Fundamentally, inherently observable events in Cyber-Physical Systems with tight coupling between cyber and physical components can result in a confidentiality violation. By observing how the physical elements react to cyber commands, adversaries can identify critical links in the system and force the cyber control algorithm to make erroneous decisions. Thus, there is a propensity for a breach in confidentiality leading to further attacks on availability or integrity. Due to the highly integrated nature of Cyber-Physical Systems, it is also extremely difficult to map the system semantics into a security framework under existing security models. The far-reaching objective of this research is to develop a science of selfobfuscating systems based on the composition of simple building blocks. A model of Nondeducibility composes the building blocks under Information Flow Security Properties. To this end, this work presents fundamental theories on external observability for basic regular networks and the novel concept of event compensation that can enforce Information Flow Security Properties at runtime --Abstract, page iii

    A Logical Method for Policy Enforcement over Evolving Audit Logs

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    We present an iterative algorithm for enforcing policies represented in a first-order logic, which can, in particular, express all transmission-related clauses in the HIPAA Privacy Rule. The logic has three features that raise challenges for enforcement --- uninterpreted predicates (used to model subjective concepts in privacy policies), real-time temporal properties, and quantification over infinite domains (such as the set of messages containing personal information). The algorithm operates over audit logs that are inherently incomplete and evolve over time. In each iteration, the algorithm provably checks as much of the policy as possible over the current log and outputs a residual policy that can only be checked when the log is extended with additional information. We prove correctness and termination properties of the algorithm. While these results are developed in a general form, accounting for many different sources of incompleteness in audit logs, we also prove that for the special case of logs that maintain a complete record of all relevant actions, the algorithm effectively enforces all safety and co-safety properties. The algorithm can significantly help automate enforcement of policies derived from the HIPAA Privacy Rule.Comment: Carnegie Mellon University CyLab Technical Report. 51 page

    Cryptographically Secure Information Flow Control on Key-Value Stores

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    We present Clio, an information flow control (IFC) system that transparently incorporates cryptography to enforce confidentiality and integrity policies on untrusted storage. Clio insulates developers from explicitly manipulating keys and cryptographic primitives by leveraging the policy language of the IFC system to automatically use the appropriate keys and correct cryptographic operations. We prove that Clio is secure with a novel proof technique that is based on a proof style from cryptography together with standard programming languages results. We present a prototype Clio implementation and a case study that demonstrates Clio's practicality.Comment: Full version of conference paper appearing in CCS 201

    On Enabling Integrated Process Compliance with Semantic Constraints in Process Management Systems

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    Key to broad use of process management systems (PrMS) in practice is their ability to foster and ease the implementation, execution, monitoring, and adaptation of business processes while still being able to ensure robust and error-free process enactment. To meet these demands a variety of mechanisms has been developed to prevent errors at the structural level (e.g., deadlocks). In many application domains, however, processes often have to comply with business level rules and policies (i.e., semantic constraints) as well. Hence, to ensure error-free executions at the semantic level, PrMS need certain control mechanisms for validating and ensuring the compliance with semantic constraints. In this paper, we discuss fundamental requirements for a comprehensive support of semantic constraints in PrMS. Moreover, we provide a survey on existing approaches and discuss to what extent they are able to meet the requirements and which challenges still have to be tackled. In order to tackle the particular challenge of providing integrated compliance support over the process lifecycle, we introduce the SeaFlows framework. The framework introduces a behavioural level view on processes which serves a conceptual process representation for constraint specification approaches. Further, it provides general compliance criteria for static compliance validation but also for dealing with process changes. Altogether, the SeaFlows framework can serve as formal basis for realizing integrated support of semantic constraints in PrMS
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