FACPL at a glance¶
FACPL: Specifying, Analysing and Enforcing Access Control Policies
The FACPL language is a formal, easy-to-use language that permits specifying access control policies. FACPL is the basis of a feasible and effective approach for defining access control systems. Various applications have been proposed, varying from e-Health to autonomic computing domains.
FACPL is equipped with a powerful Integrated Development Environment (IDE) and a Java library, supporting access control system developers in the tasks of specifying, analysing and enforcing FACPL policies. Figure 1 shows the toolchain enabling the use of the language.
Developers can use the IDE, in the form of an Eclipse plugin, for specifying the desired policies in FACPL syntax, by taking advantage of the supporting features provided by the environment. The IDE automatically produces a set of Java classes enforcing the FACPL policies and of SMT-LIB files enabling the automatic analysis of policies. The Java FACPL library provides the compile- and run-time support for validating and enforcing the generated Java policies in real systems. The use of the SMT-LIB code and of the Z3 constraint solver offers effective analysis means. Furthermore, the toolchain offers a (partial) interoperability with the XACML standard, commonly used to deploy real-world access control systems. See Section 9.1 of this FACPL paper for further details on XACML vs. FACPL interoperability.
FACPL Evaluation Process¶
Policies control system resources by means of a particular evaluation process, which relies on two main components: the Policy Decision Point (PDP) and the Policy Enforcement Point (PEP). The former calculates the authorization decision for an access request, and the latter enforces such decision in the system. Figure 2 shows the FACPL evaluation process.
Each controlled resource is paired with one or more FACPL policies, which define the access control rules expressing the credentials necessary to gain access to the resource. These policies are stored within the Policy Repository (PR) that makes them available to the PDP (step 1), which has the task of deciding whether to grant access to resources or not. The evaluation of a request is organized in the following steps.
- A request to access a resource is received by the PEP (step 2) and it is encoded as a FACPL request containing the credentials expressed as attribute elements (step 3). An attribute is a pair (name, value) representing a security-relevant information.
- The context handler sends the request to the PDP (step 4) and can add environmental attributes to the request, as e.g. the request receiving time, which may be needed for the evaluation process.
- The PDP computes the PDP response for the request by checking the attributes, that may belong either to the request or to the context (steps 5-8), against the controls contained in the policies. The PDP response contains an authorization decision and, possibly, some obligations.
- The PDP response is sent to the PEP, that, by appropriate obligation services, must discharge all possibly present obligations (steps 9-11).
- On the basis of the result of obligations discharge, the PEP computes the final decision (steps 12-13). This decision, that could differ from the PDP one, is the overall outcome of the evaluation process.
Notably, obligations are additional actions connected to the access control system and might correspond to, e.g., updating a log file, sending a message, generating an event or executing an action.