EasyCrypt: Computer-Aided Cryptographic Proofs

EasyCrypt is a toolset for reasoning about relational properties of probabilistic computations with adversarial code. Its main application is the construction and verification of game-based cryptographic proofs.

Table of Contents

• EasyCrypt: Computer-Aided Cryptographic Proofs
  • Installation requirements
  • Via OPAM
    • Installing requirements using OPAM (POSIX systems)
    • Installing requirements using OPAM (non-POSIX systems)
  • Via NIX
• Configuring Why3
  • Note on prover versions
• Installing/Compiling EasyCrypt
• Proof General Front-End
  • Installing using opam
  • Installing from sources

Installation requirements

EasyCrypt uses the following third-party tools/libraries:

• OCaml (>= 4.08)

  Available at https://ocaml.org/

• OCamlbuild

• Why3 (>= 1.7.x, < 1.8)

  Available at http://why3.lri.fr/

  Why3 must be installed with a set a provers. See http://why3.lri.fr/#provers

  Why3 libraries must be installed (make byte && make install-lib)

• Menhir http://gallium.inria.fr/~fpottier/menhir/

• OCaml Batteries Included http://batteries.forge.ocamlcore.org/

• OCaml PCRE (>= 7) https://github.com/mmottl/pcre-ocaml

• OCaml Zarith https://forge.ocamlcore.org/projects/zarith

• OCaml ini-files http://archive.ubuntu.com/ubuntu/pool/universe/o/ocaml-inifiles/

On POSIX/Win32 systems (GNU/Linux, *BSD, OS-X), we recommend that users install EasyCrypt and all its dependencies via opam.

Via OPAM

Installing requirements using OPAM 2 (POSIX systems)

Opam can be easily installed from source or via your packages manager:

• On Ubuntu and derivatives:

    $> add-apt-repository ppa:avsm/ppa
    $> apt-get update
    $> apt-get install ocaml ocaml-native-compilers camlp4-extra opam

• On Fedora/OpenSUSE:

    $> sudo dnf update
    $> sudo dnf install ocaml ocaml-docs ocaml-camlp4-devel opam

• On MacOSX using brew:

    $> brew install ocaml opam

Once opam and ocaml has been successfully installed run the following:

$> opam init
$> eval $(opam env)

For any issues encountered installing opam see:

• [https://opam.ocaml.org/doc/Install.html] for detailed opam installation instructions.

• [https://opam.ocaml.org/doc/Usage.html] for how to initialize opam.

You can then install all the needed dependencies via the opam OCaml packages manager.

0. Optionally, switch to a dedicated compiler for EasyCrypt:

     $> opam switch create easycrypt $OVERSION

   where $OVERSION is a valid OCaml version (e.g. ocaml-base-compiler.4.07.0)

1. Add the EasyCrypt package from repository:

     $> opam pin -yn add easycrypt https://github.com/EasyCrypt/easycrypt.git

2. Optionally, use opam to install the system dependencies:

     $> opam install opam-depext
     $> opam depext easycrypt

3. Install EasyCrypt's dependencies:

     $> opam install --deps-only easycrypt
     $> opam install alt-ergo

   If you get errors about ocamlbuild failing because it's already installed, the check can be skipped with the following:

     CHECK_IF_PREINSTALLED=false opam install --deps-only easycrypt

4. You can download extra provers at the following URLs:

   • Z3: [https://github.com/Z3Prover/z3]
   • CVC4: [https://cvc4.github.io/]

Installing requirements using OPAM (non-POSIX systems)

You can install all the needed dependencies via the opam OCaml packages manager.

1. Install the opam Ocaml packages manager, following the instructions at:

   https://fdopen.github.io/opam-repository-mingw/installation/

2. Add the EasyCrypt package from repository:

     $> opam pin -yn add easycrypt https://github.com/EasyCrypt/easycrypt.git

3. Use opam to install the system dependencies:

     $> opam install depext depext-cygwinports
     $> opam depext easycrypt

4. Install EasyCrypt's dependencies:

     $> opam install --deps-only easycrypt
     $> opam install alt-ergo

5. You can download extra provers at the following URLs:

   • Z3: [https://github.com/Z3Prover/z3]
   • CVC4: [https://cvc4.github.io/]

Via NIX

First, install the Nix package manager by following these instructions.

Then, at the root of the EasyCrypt source tree, type:

```
$> make nix-build
```

Once completed, you will find the EasyCrypt binary in result/bin.

You can also run

```
$> make nix-build-with-provers
```

to install EasyCrypt along with a set of provers.

For getting a development environment, you can run:

```
$> make nix-develop
```

These will install all the required dependencies, a set of provers and will then drop you into a shell. From there, simply run make to compile EasyCrypt.

Note on Prover Versions

Why3 and SMT solvers are independent pieces of software with their own version-specific interactions. Obtaining a working SMT setup may require installing specific versions of some of the provers.

At the time of writing, we depend on Why3 1.7.x, which supports the following prover versions:

• Alt-Ergo 2.5.2
• CVC4 1.8
• CVC5 1.0.8
• Z3 4.12.x

alt-ergo can be installed using opam, if you do you can use pins to select a specific version (e.g, opam pin alt-ergo 2.5.2).

Installing/Compiling EasyCrypt

If installing from source, running

$> make
$> make install

builds and install EasyCrypt (under the binary named easycrypt), assuming that all dependencies have been successfully installed. If you choose not to install EasyCrypt system wide, you can use the binary ec.native that is located at the root of the source tree.

EasyCrypt comes also with an opam package. Running

$> opam install easycrypt

installs EasyCrypt and its dependencies via opam. In that case, the EasyCrypt binary is named easycrypt.

Configuring Why3

Initially, and after the installation/removal/update of SMT provers, you need to (re)configure Why3 via the following easycrypt command:

$> easycrypt why3config

EasyCrypt stores the Why3 configuration file under

$XDG_CONFIG_HOME/easycrypt/why3.conf

EasyCrypt allows you, via the option -why3, to load a Why3 configuration file from a custom location. For instance:

$> easycrypt why3config -why3 $WHY3CONF.conf
$> easycrypt -why3 $WHY3CONF.conf

where $WHY3CONF must be replaced by some custom location.

Proof General Front-End

EasyCrypt mode has been integrated upstream. Please, go to https://github.com/ProofGeneral/PG and follow the instructions.

Examples

Examples of how to use EasyCrypt are in the examples directory. You will find basic examples at the root of this directory, as well as a more advanced example in the MEE-CBC sub-directory and a tutorial on how to use the complexity system in cost sub-directory.