Skip to content


Repository files navigation


This is the compiler for the Flexible and Constant Time cryptographic programming language. FaCT is a domain-specific language that aids you in writing constant-time code for cryptographic routines that need to be free from timing side channels.

Useful links:


To build the compiler, you can either build from source or download a pre-built release. We recommend building from source if possible.

Virtual machine image

You can download a VM image pre-configured for building the FaCT compiler and case studies. The file fact.ova should have a SHA256 sum of 089398c85c5074d911c2f2b67ca22df453235e8733f1eb283c71717cf70f714c.

Using Docker

If you have docker installed, you can load our docker image with the build environment already installed:

cd docker/

Once inside the docker shell, run the following to finish setting up the environment:

cd FaCT/
eval $(opam config env)

Setting up the build environment

FaCT is developed using OCaml 4.06.0 and LLVM 6.0.

Using a local environment

Building FaCT has been tested on Ubuntu 16.04, 18.04, and macOS.

1. Install System Dependencies

Ubuntu (16.04 & 18.04)

sudo apt install llvm-6.0 clang-6.0 cmake libgmp-dev m4 pkg-config


These instructions require Homebrew

brew install cmake gmp m4 pkg-config
brew install llvm@6 --with-toolchain

Note: This does not put the proper version of clang on your PATH. You will need to run:

export PATH="$(brew --prefix llvm@6)/bin:$PATH"

2. Install OCaml + packages

We recommend installing the opam package manager to manage OCaml and package dependencies:

sh <(curl -sL

Then, install OCaml and the libraries:

opam init
eval $(opam config env)
opam switch create 4.06.0
eval $(opam config env)
opam switch import ocamlswitch.txt

Finally, make sure the Z3 lib is available to the OCaml compiler:

export LD_LIBRARY_PATH="$HOME/.opam/4.06.0/lib/z3:$LD_LIBRARY_PATH"

3. Configure Paths

The FaCT compiler depends on the LLVM 6.0 toolchain at runtime, and expects binaries with -6.0 suffixes. Ensure that clang-6.0 is in your PATH:

clang-6.0 --version

Compiling FaCT

You can now build the compiler:

oasis setup

This will produce the factc executable.


Basic Usage

Run ./factc <source files> to compile a FaCT program.

Link to a C library

FaCT is designed to be called from C code. Compiling FaCT source files will output an object file, which can then be linked to a C file. As an example:

cd example/
../factc -generate-header example.fact
clang-6.0 -c main.c
clang-6.0 -o final main.o example.o

You can then run the executable:



Many debugging options and intermediate data structures are available. Run ./factc -help for all options.


We thank the anonymous PLDI and PLDI AEC reviewers for their suggestions and insightful comments.


Flexible and Constant Time Programming Language







No releases published


No packages published