There is an increasing trend for businesses to migrate their systems towards the cloud. Security concerns that arise when outsourcing data and computation to the cloud include data confidentiality and privacy. Given that a tremendous amount of data is being generated everyday from plethora of devices equipped with sensing capabilities, we focus on the problem of access controls over live streams of data based on triggers or sliding windows, which is a distinct and more challenging problem than access control over archival data. Specifically, we investigate secure mechanisms for outsourcing access control enforcement for stream data to the cloud. We devise a system that allows data owners to specify fine-grained policies associated with their data streams, then to encrypt the streams and relay them to the cloud for live processing and storage for future use. The access control policies are enforced by the cloud, without the latter learning about the data, while ensuring that unauthorized access is not feasible. To realize these ends, we employ a novel cryptographic primitive, namely proxy-based attribute-based encryption, which not only provides security but also allows the cloud to perform expensive computations on behalf of the users. Our approach is holistic, in that these controls are integrated with an XML based framework (XACML) for high-level management of policies. Experiments with our prototype demonstrate the feasibility of such mechanisms, and early evaluations suggest graceful scalability with increasing numbers of policies, data streams and users.
Existing works on access control for stream data assume trusted domains and focus on the specification and enforcement of access policies @cite_31 @cite_5 @cite_2 . They are different to our work which considers outsourcing access control to an untrusted environment. Similarly, previous works that use XACML for fine-grained access control have also focused on trusted domains @cite_23 . We use XACML only for policy management, and rely on encryption schemes for policy enforcement.
@cite_5 @cite_31 @cite_23 @cite_2
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A widely adopted security mechanism is the specification of access control policies by means of the XACML language. In this paper, we propose a framework, called X-CREATE, for the systematic generation of test inputs (XACML requests). Differently from existing tools, XCREATE exploits the XACML Context Schema. In particular, the tool applies a XML-based methodology (XPT) to systematically produce a set of intermediate instances, covering the XACML Context Schema. Moreover, for request generation, X-CREATE applies a procedure for parsing the policy under test and assigning values to the generated intermediate instances. The aim of the proposed framework is twofold: testing of policy evaluation engines and testing of access control policies. The experimental results show that the fault detection effectiveness of X-CREATE is similar or higher than that of existing approaches. Attribute-based access control (ABAC) has attracted considerable interest in recent years, resulting in an extensive literature on the subject, including the standardized XML-based language XACML. ABAC policies written in languages like XACML have a tree-like structure in which leaf nodes are associated with authorization decisions and non-leaf nodes are associated with decision-combining algorithms. In this paper, we consider the expressive power of the rule- and policy-combining algorithms defined by the XACML standard. In particular, we identify unexpected dependencies between the combining algorithms and demonstrate that there exist useful combining algorithms that cannot be expressed by any combination of XACML combining algorithms. We briefly discuss the decision operators defined in the PTaCL language, an abstract language for defining ABAC policies, and the advantages of replacing the XACML combining algorithms with the PTaCL operators. Following this, we review results in the literature on multi-valued logic and introduce the notion of canonically complete policy languages. We discuss important practical advantages of canonically complete policy languages, primarily in simplifying policy specification and providing efficiently enforceable policies. Finally, we propose a new policy authorization language PTaCL which is canonically complete and show it is capable of expressing any arbitrary policy in a normal form and discuss the advantages of using PTaCL over existing policy languages such as XACML and PTaCL. Testing access control policies relies on their execution on a security engine and the evaluation of the correct responses. Coverage measures can be adopted to know which parts of the policy are most exercised. This paper proposes an access control infrastructure for enabling the coverage criterion selection, the monitoring of the policy execution and the analysis of the policy coverage assessment. The framework is independent from the policy specification language and does not require the instrumentation of the evaluation engine. We show an instantiation of the proposed infrastructure for assessing the XACML policy testing. Access control policies in distributed systems, particularly implemented in the XACML standard language, are increasingly complex. Faults may exist in complex policies for various reasons such as misunderstanding of the access control requirements, omissions, and coding errors. These faults, if not removed before deployment, may lead to unauthorized accesses or denial of service. Manual localization of these faults, however, can be a challenging task. Inspired by spectrum-based fault localization for software debugging, this paper presents an approach for automatically localizing the fault(s) in a given XACML policy by exploring test coverage information of the policy elements. We investigate two test coverage criteria (i.e., reachability and firing) of policy elements and 14 scoring methods for ranking policy elements to determine the fault location(s). To evaluate the fault localization methods, we have used real-world policy files with different levels of complexity and a large number of policy mutants with one or two seeded faults. The experiment results show that the firing-based Naish2 and CBI-Inc methods are effective in fault localization of XACML policies.