Hax

hax is a tool for high assurance translations that translates a large subset of Rust into formal languages such as F* or Coq. This extends the scope of the hacspec project, which was previously a DSL embedded in Rust, to a usable tool for verifying Rust programs.

So what is hacspec now?

hacspec is the functional subset of Rust that can be used, together with a hacspec standard library, to write succinct, executable, and verifiable specifications in Rust. These specifications can be translated into formal languages with hax.

Usage

Hax is a cargo subcommand. The command cargo hax accepts the following subcommands:

• into (cargo hax into BACKEND): translate a Rust crate to the backend BACKEND (e.g. fstar, coq).
• json (cargo hax json): extract the typed AST of your crate as a JSON file.

Note:

• BACKEND can be fstar, coq or easycrypt. cargo hax into --help gives the full list of supported backends.
• The subcommands cargo hax, cargo hax into and cargo hax into <BACKEND> takes options. For instance, you can cargo hax into fstar --z3rlimit 100. Use --help on those subcommands to list all options.

Installation

Manual installation

1. Make sure to have the following installed on your system:

• opam (opam switch create 4.14.1)
• rustup
• nodejs
• jq

2. Clone this repo: git clone [email protected]:hacspec/hax.git && cd hax
3. Run the setup.sh script: ./setup.sh.
4. Run cargo-hax --help

Nix

This should work on Linux, MacOS and Windows.

Prerequisites: Nix package manager (with flakes enabled)

• Either using the Determinate Nix Installer, with the following bash one-liner:

  curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install

• or following those steps.

• Run hax on a crate directly to get F*/Coq/... (assuming you are in the crate's folder):

  • nix run github:hacspec/hax -- into fstar extracts F*.

• Install hax: nix profile install github:hacspec/hax, then run cargo hax --help anywhere

• Note: in any of the Nix commands above, replace github:hacspec/hax by ./dir to compile a local checkout of hax that lives in ./some-dir

• Setup binary cache: using Cachix, just cachix use hax

Using Docker

1. Clone this repo: git clone [email protected]:hacspec/hax.git && cd hax
2. Build the docker image: docker build -f .docker/Dockerfile . -t hax
3. Get a shell: docker run -it --rm -v /some/dir/with/a/crate:/work hax bash
4. You can now run cargo-hax --help (notice here we use cargo-hax instead of cargo hax)

Supported Subset of the Rust Language

Hax intends to support full Rust, with the two following exceptions, promoting a functional style:

1. no unsafe code (see hacspec#417);
2. mutable references (aka &mut T) on return types or when aliasing (see hacspec#420).

Each unsupported Rust feature is documented as an issue labeled unsupported-rust. When the issue is labeled wontfix-v1, that means we don't plan on supporting that feature soon.

Quicklinks:

• 🔨 Rejected rust we want to support;
• 💭 Rejected rust we don't plan to support in v1.

Examples

There's a set of examples that show what hax can do for you. Please check out the examples directory.

Hacking on Hax

Edit the sources (Nix)

Just clone & cd into the repo, then run nix develop .. You can also just use direnv, with editor integration.

Structure of this repository

• rust-frontend/: Rust library that hooks in the rust compiler and extract its internal typed abstract syntax tree THIR as JSON.
• engine/: the simplification and elaboration engine that translates programs from the Rust language to various backends (see engine/backends/).
• cli/: the hax subcommand for Cargo.

Recompiling

You can use the .utils/rebuild.sh script (which is available automatically as the command rebuild when using the Nix devshell):

• rebuild: rebuild the Rust then the OCaml part;
• rebuild TARGET: rebuild the TARGET part (TARGET is either rust or ocaml).

Publications & Other material

• 📕 Tech report
• 📕 HACSpec: A gateway to high-assurance cryptography
• 📕 Original hacspec paper

Secondary literature, using hacspec:

• 📕 Last yard

Contributing

Before starting any work please join the Zulip chat, start a discussion on Github, or file an issue to discuss your contribution.

Acknowledgements

Zulip graciously provides the hacspec & hax community with a "Zulip Cloud Standard" tier.