Vincent C. Hu

Attribute-Based Access Control

Attribute-based access control (ABAC) is a flexible approach that can implement AC policies limited only by the computational language and the richness of the available attributes, making it ideal for many distributed or rapidly changing environments.

Conformance Checking of Access Control Policies Specified in XACML

Access control is one of the most fundamental and widely used security mechanisms. Access control mechanisms control which principals such as users or processes have access to which resources in a system. To facilitate managing and maintaining access control, access control policies are increasingly written in specification languages such as XACML. The specification of access control policies itself is often a challenging problem. Furthermore, XACML is intentionally designed to be generic: it provides the freedom in describing access control policies, which are well-known or invented ones. But the flexibility and expressiveness provided by XACML come at the cost of complexity, verbosity, and lack of desirable-property enforcement. Often common properties for specific access control policies may not be satisfied when these policies are specified in XACML, causing the discrepancy between what the policy authors intend to specify and what the actually specified XACML policies reflect. In this position paper, we propose an approach for conducting conformance checking of access control policies specified in XACML based on existing verification and testing tools for XACML policies.

MODEL CHECKING FOR VERIFICATION OF MANDATORY ACCESS CONTROL MODELS AND PROPERTIES

Mandatory access control (MAC) mechanisms control which users or processes have access to which resources in a system. MAC policies are increasingly specified to facilitate managing and maintaining access control. However, the correct specification of the policies is a very challenging problem. To formally and precisely capture the security properties that MAC should adhere to, MAC models are usually written to bridge the rather wide gap in abstraction between policies and mechanisms. In this paper, we propose a general approach for property verification for MAC models. The approach defines a standardized structure for MAC models, providing for both property verification and automated generation of test cases. The approach expresses MAC models in the specification language of a model checker and expresses generic access control properties in the property language. Then the approach uses the model checker to verify the integrity, coverage, and confinement of these properties for the MAC models and finally generates test cases via combinatorial covering array for the system implementations of the models.

Composing and combining policies under the policy machine

As a major component of any host, or network operating system, access control mechanisms come in a wide variety of forms, each with their individual attributes, functions, methods for configuring policy, and a tight coupling to a class of policies. To afford generalized protection, NIST has initiated a project in pursuit of a standardized access control mechanism, referred to as the Policy Machine (PM) that requires changes only in its configuration in the enforcement of arbitrary and organization specific attribute-based access control policies. Included among the PMs enforceable policies are combinations of policy instances (e.g., Role-Based Access Control and Multi-Level Security). In our effort to devise a generic access control mechanism, we construct the PM in terms of what we believe to be abstractions, properties and functions that are fundamental to policy configuration and enforcement. In its protection of objects under one or more policy instances, the PM categorizes users and objects and their attributes into policy classes, and transparently enforces these policies through a series of fixed PM functions, that are invoked in response to user or subject (process) access requests.

Property Verification for Generic Access Control Models

To formally and precisely capture the security properties that access control should adhere to, access control models are usually written to bridge the rather wide gap in abstraction between policies and mechanisms. In this paper, we propose a new general approach for property verification for access control models. The approach defines a standardized structure for access control models, providing for both property verification and automated generation of test cases. The approach expresses access control models in the specification language of a model checker and expresses generic access control properties in the property language. Then the approach uses the model checker to verify these properties for the access control models and generates test cases via combinatorial covering array for the system implementations of the models.

ACPT: A Tool for Modeling and Verifying Access Control Policies

Access control mechanisms are a widely adopted technology for information security. Since access decisions (i.e., permit or deny) on requests are dependent on access control policies, ensuring the correct modeling and implementation of access control policies is crucial for adopting access control mechanisms. To address this issue, we develop a tool, called ACPT (Access Control Policy Testing), that helps to model and implement policies correctly during policy modeling, implementation, and verification.

The Policy Machine for Security Policy Management

Many different access control policies and models have been developed to suit a variety of goals; these include Role-Based Access Control, One-directional Information Flow, Chinese Wall, Clark-Wilson, N-person Control, and DAC, in addition to more informal ad hoc policies. While each of these policies has a particular area of strength, the notational differences between these policies are substantial. As a result it is difficult to combine them, both in making formal statements about systems which are based on differing models and in using more than one access control policy model within a given system. Thus, there is a need for a unifying formalism which is general enough to encompass a range of these policies and models. In this paper, we propose an open security architecture called the Policy Machine (PM) that would meet this need. We also provide examples showing how the PM specifies and enforces access control polices.

Assessing Quality of Policy Properties in Verification of Access Control Policies

Access control policies are often specified in declarative languages. In this paper, we propose a novel approach, called mutation verification, to assess the quality of properties specified for a policy and, in doing so, the quality of the verification itself. In our approach, given a policy and a set of properties, we first mutate the policy to generate various mutant policies, each with a single seeded fault. We then verify whether the properties hold for each mutant policy. If the properties still hold for a given mutant policy, then the quality of these properties is determined to be insufficient in guarding against the seeded fault, indicating that more properties are needed to augment the existing set of properties to provide higher confidence of the policy correctness. We have implemented Mutaver, a mutation verification tool for XACML, and applied it to policies and properties from a real-world software system.

Security policy verification for multi-domains in cloud systems

The cloud is a modern computing paradigm with the ability to support a business model by providing multi-tenancy, scalability, elasticity, pay as you go and self-provisioning of resources by using broad network access. Yet, cloud systems are mostly bounded to single domains, and collaboration among different cloud systems is an active area of research. Over time, such collaboration schemas are becoming of vital importance since they allow companies to diversify their services on multiple cloud systems to increase both uptime and usage of services. The existence of an efficient management process for the enforcement of security policies among the participating cloud systems would facilitate the adoption of multi-domain cloud systems. An important issue in collaborative environments is secure inter-operation. Stemmed from the absence of relevant work in the area of cloud computing, we define a model checking technique that can be used as a management service/tool for the verification of multi-domain cloud policies. Our proposal is based on NIST’s (National Institute of Standards and Technology) generic model checking technique and has been enriched with RBAC reasoning. Current approaches, in Grid systems, are capable of verifying and detect only conflicts and redundancies between two policies. However, the latter cannot overcome the risk of privileged user access in multi-domain cloud systems. In this paper, we provide the formal definition of the proposed technique and security properties that have to be verified in multi-domain cloud systems. Furthermore, an evaluation of the technique through a series of performance tests is provided.

Extensible Access Control Markup Language (XACML) and Next Generation Access Control (NGAC)

Extensible Access Control Markup Language (XACML) and Next Generation Access Control (NGAC) are very different attribute based access control standards with similar goals and objectives. An objective of both is to provide a standardized way for expressing and enforcing vastly diverse access control policies in support of various types of data services. The two standards differ with respect to the manner in which access control policies and attributes are specified and managed, and decisions are computed and enforced. This paper is presented as a consolidation and refinement of public draft NIST SP 800-178 [21], describing, and comparing these two standards.