A Calculus for Flow-Limited Authorization

TL;DR

This paper introduces FLAC, a formal calculus for modeling and reasoning about dynamic authorization mechanisms that ensure confidentiality and integrity through strong security guarantees like noninterference.

Contribution

FLAC extends the Dependency Core Calculus to incorporate dynamic authorization, providing a formal framework with proven security properties for complex authorization scenarios.

Findings

FLAC guarantees noninterference and robust declassification.

The calculus is expressive enough for various dynamic authorization mechanisms.

Formal proofs validate security properties for all FLAC programs.

Abstract

Real-world applications routinely make authorization decisions based on dynamic computation. Reasoning about dynamically computed authority is challenging. Integrity of the system might be compromised if attackers can improperly influence the authorizing computation. Confidentiality can also be compromised by authorization, since authorization decisions are often based on sensitive data such as membership lists and passwords. Previous formal models for authorization do not fully address the security implications of permitting trust relationships to change, which limits their ability to reason about authority that derives from dynamic computation. Our goal is an approach to constructing dynamic authorization mechanisms that do not violate confidentiality or integrity. The Flow-Limited Authorization Calculus (FLAC) is a simple, expressive model for reasoning about dynamic authorization as well as an information flow control language for securely implementing various authorization mechanisms. FLAC combines the insights of two previous models: it extends the Dependency Core Calculus with features made possible by the Flow-Limited Authorization Model. FLAC provides strong end-to-end information security guarantees even for programs that incorporate and implement rich dynamic authorization mechanisms. These guarantees include noninterference and robust declassification, which prevent attackers from influencing information disclosures in unauthorized ways. We prove these security properties formally for all FLAC programs and explore the expressiveness of FLAC with several examples.