DY* is a formal verification framework for the symbolic security analysis of cryptographic protocol code written in the F* programming language. Unlike automated symbolic provers, our framework accounts for advanced protocol features like unbounded loops and mutable recursive data structures, as well as low-level implementation details like protocol state machines and message formats, which are often at the root of real-world attacks.

Our work extends a long line of research on using dependent type systems for this task, but takes a fundamentally new approach by explicitly modeling the global trace-based semantics within the framework, hence bridging the gap between trace-based and type-based protocol analyses. This approach enables us to uniformly, precisely, and soundly model, for the first time using dependent types, long-lived mutable protocol state, equational theories, fine-grained dynamic corruption, and trace-based security properties like forward secrecy and post-compromise security.

DY* is built as a library of F* modules that includes a model of low-level protocol execution, a Dolev-Yao symbolic attacker, and generic security abstractions and lemmas, all verified using F*. The library exposes a high-level API that facilitates succinct security proofs for protocol code.

We have demonstrated the effectiveness of this approach through several in-depth symbolic security analyses. For example, we have carried out the first mechanized proof of Signal that accounts for forward and post-compromise security over an unbounded number of protocol rounds. Please see our GitHub repository for the code.