Due to ubiquitous use of software services, protecting the confidentiality of private information stored in compute clouds is becoming an increasingly critical problem. Although access control specification languages and libraries provide mechanisms for protecting confidentiality of information, without verification and validation techniques that can assist developers in writing policies, complex policy specifications are likely to have errors that can lead to unintended and unauthorized access to data, possibly with disastrous consequences. In this paper, we present a quantitative and differential policy analysis framework that not only identifies if one policy is more permissive than another policy, but also quantifies the relative permissiveness of access control policies. We quantify permissiveness of policies using a model counting constraint solver. We present a heuristic that transforms constraints extracted from access control policies and significantly improves the model counting performance. We demonstrate the effectiveness of our approach by applying it to policies written in Amazon's AWS Identity and Access Management (IAM) policy language and Microsoft's Azure policy language.

quacky is a tool for quantifying permissiveness of access control policies in the cloud. Given a policy, quacky translates it into a SMT formula and uses a model counting constraint solver to quantify permissiveness. When given multiple policies, quacky not only determines which policy is more permissive, but also quantifies the relative permissiveness between the policies. With quacky, policy authors can automatically analyze complex policies, helping them ensure that there is no unintended access to private data. quacky supports access control policies written in the Amazon Web Services (AWS) Identity and Access Management (IAM), Microsoft Azure, and Google Cloud Platform (GCP) policy languages. It has command-line and web interfaces. It is open-source and available at https://github.com/vlab-cs-ucsb/quacky.