Automated Synthesis of Privacy-Preserving Distributed Applications

We introduce a framework for the automated synthesis of security-sensitive distributed applications. The central idea is to provide the programmer with a high-level declarative language for specifying the system and the intended security properties, abstracting away from any cryptographic details. A compiler takes as input such high-level specifications and automatically produces the corresponding cryptographic implementations (i.e., cryptographic library, cryptographic protocols, and F source code). In this work, we focus on two important, and seemingly contradictory, security properties, namely, authorization and privacy. On the one hand, the access to sensitive resources should be granted only to authorized users; on the other hand, these users would like to share as little personal information as possible with third parties. These opposing goals make it challenging to enforce privacy-aware authorization policies in a distributed setting. The high-level declarative language builds on Evidential DKAL, a logic for authorization polices of decentralized systems, which we extend to reason about privacy policies. Specifically, the traditional says modality from authorization logics is accompanied by existential quantification in order to express the secrecy of sensitive information. The cryptographic realization of privacy-aware authorization policies is obtained by a powerful combination of digital signatures and zero-knowledge proofs. This approach is general and can be seen as a privacy-enabling plugin for existing authorization languages and proof-carrying authorization architectures. We proved that the implementations output by the compiler enforce the intended authorization policies and we conducted an experimental evaluation to demonstrate the feasibility of our approach.