cryptol/README.md

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# Cryptol, version 2

    This version of Cryptol is (C) 2013-2017 Galois, Inc., and
    distributed under a standard, three-clause BSD license. Please see
    the file LICENSE, distributed with this software, for specific
    terms and conditions.

# What is Cryptol?

The Cryptol specification language was designed by Galois for the
NSA's Trusted Systems Research Group as a public standard for
specifying cryptographic algorithms. A Cryptol reference specification
can serve as the formal documentation for a cryptographic module.
Unlike current specification mechanisms, Cryptol is fully executable,
allowing designers to experiment with their programs incrementally as
their designs evolve.

This release is an interpreter for version 2 of the Cryptol
language. The interpreter includes a `:check` command, which tests
predicates written in Cryptol against randomly-generated test vectors
(in the style of
[QuickCheck](http://hackage.haskell.org/package/QuickCheck)). There is
also a `:prove` command, which calls out to SMT solvers, such as
Yices, Z3, or CVC4, to prove predicates for all possible inputs.

# Getting Cryptol Binaries

Cryptol binaries for Mac OS X, Linux, and Windows are available from
the GitHub
[releases page](https://github.com/GaloisInc/cryptol/releases). Mac OS
X and Linux binaries are distributed as a tarball which you can
extract to a location of your choice. Windows binaries are distributed
as an `.msi` installer package which places a shortcut to the Cryptol
interpreter in the Start menu.

On Mac OS X, Cryptol is also available via
[Homebrew](http://brew.sh/). Simply run `brew update && brew install
cryptol` to get the latest stable version.

## Getting Z3

Cryptol currently uses Microsoft Research's [Z3 SMT
solver](https://github.com/Z3Prover/z3) by default to solve constraints
during type checking, and as the default solver for the `:sat` and
`:prove` commands. You can download Z3 binaries for a variety of
platforms from their [releases page](https://github.com/Z3Prover/z3/releases).

Cryptol generally requires the most recent version of Z3, which at the
time of writing this file is 4.5.0. Note that if you install Cryptol
using Homebrew, the appropriate version of Z3 will be installed
automatically.

After installation, make sure that `z3` (or `z3.exe` on Windows)
is on your PATH.

### Note for 64-bit Linux Users

On some 64-bit Linux configurations, 32-bit binaries do not work. This
can lead to unhelpful error messages like `z3: no such file or
directory`, even when `z3` is clearly present. To fix this, either
install 32-bit compatibility packages for your distribution, or
download the `x64` version of Z3.

# Building Cryptol From Source

In addition to the binaries, the Cryptol source is available publicly
on [GitHub](https://github.com/GaloisInc/cryptol).

Cryptol builds and runs on various flavors of Linux, Mac OS X, and
Windows. We regularly build and test it in the following environments:

- Mac OS X 10.10 64-bit
- CentOS 6 32/64-bit
- Windows 7 32-bit

## Prerequisites

Cryptol is developed using GHC 7.10.2 and cabal-install 1.22, though
it is still tested with the previous major version of GHC. The easiest
way to get the correct versions is to follow the instructions on the
[haskell.org downloads page](https://www.haskell.org/downloads).

Some supporting non-Haskell libraries are required to build
Cryptol. Most should already be present for your operating system, but
you may need to install the following:

- [The GNU Multiple Precision Arithmetic Library (GMP)](https://gmplib.org/)
- [ncurses](https://www.gnu.org/software/ncurses/)

You'll also need [Z3](#getting-z3) installed when running Cryptol.

## Building Cryptol

From the Cryptol source directory, run:

    make

This will build Cryptol in place. From there, there are additional targets:

- `make run`: run Cryptol in the current directory
- `make test`: run the regression test suite (note: 4 failures is expected)
- `make docs`: build the Cryptol documentation (requires
  [pandoc](http://johnmacfarlane.net/pandoc/) and
  [TeX Live](https://www.tug.org/texlive/))
- `make tarball`: build a tarball with a relocatable Cryptol binary and documentation
- `make dist`: build a platform-specific distribution. On all
  platforms except Windows, this is currently equivalent to `make
  tarball`. On Windows, this will build an `.msi` package using
  [WiX Toolset 3.8](http://wixtoolset.org/), which must be installed
  separately.

## Installing Cryptol

If you run `cabal install` in your source directory after running one
of these `make` targets, you will end up with a binary in
`.cabal-sandbox/bin/cryptol`. You can either use that binary directly,
or use the results of `tarball` or `dist` to install Cryptol in a
location of your choice.

## Configuring Cryptol

Cryptol depends on several external files for complete operation. These
files are contained in the `lib` directory of the Cryptol repository. If
you install with `cabal install`, these files will be automaticall
copied into a directory that the `cryptol` executable can find. If you
install in other ways, you will have to do more manual configuration.
There are two options:

* Copy the contents of the `lib` directory into `$HOME/.cryptol`.

* Set the `CRYPTOLPATH` environment variable to name some other
  directory that contains those files.

# Contributing

We believe that anyone who uses Cryptol is making an important
contribution toward making Cryptol a better tool. There are many ways
to get involved.

## Users

If you write Cryptol programs that you think would benefit the
community, fork the GitHub repository, and add them to the
`examples/contrib` directory and submit a pull request.

We host a Cryptol mailing list, which
you can [join here](http://community.galois.com/mailman/listinfo/cryptol-users).

If you run into a bug in Cryptol, if something doesn't make sense in
the documentation, if you think something could be better, or if you
just have a cool use of Cryptol that you'd like to share with us, use
the issues page on [GitHub](https://github.com/GaloisInc/cryptol), or
send email to <cryptol@galois.com>.

## Developers

If you'd like to get involved with Cryptol development, see the list of
[low-hanging fruit](https://github.com/GaloisInc/cryptol/labels/low-hanging%20fruit). These
are tasks which should be straightforward to implement. Make a
fork of this GitHub repository, send along pull requests and we'll
be happy to incorporate your changes.

### Repository Structure

- `/cryptol`: Haskell sources for the front-end `cryptol` executable
  and read-eval-print loop
- `/docs`: LaTeX and Markdown sources for the Cryptol documentation
- `/examples`: Cryptol sources implementing several interesting
  algorithms
- `/lib`: Cryptol standard library sources
- `/src`: Haskell sources for the `cryptol` library (the bulk of the
  implementation)
- `/tests`: Haskell sources for the Cryptol regression test suite, as
  well as the Cryptol sources and expected outputs that comprise that
  suite

# Where to Look Next

The `docs` directory of the installation package contains an
introductory book, the `examples` directory contains a number of
algorithms specified in Cryptol.

If you are familiar with version 1 of Cryptol, you should read the
`Version2Changes` document in the `docs` directory.

Cryptol is still under active development at Galois. We are also
building tools that consume both Cryptol specifications and
implementations in (for example) C or Java, and can (with some amount
of work) allow you to verify that an implementation meets its
specification. Email us at <cryptol@galois.com> if you're interested
in these capabilities.

# Thanks!

We hope that Cryptol is useful as a tool for educators and students,
commercial and open source authors of cryptographic implementations,
and by cryptographers to

 * specify cryptographic algorithms
 * check or prove properties of algorithms
 * generate test vectors for testing implementations
 * experiment with new algorithms

## Acknowledgements

Cryptol has been under development for over a decade with many people
contributing to its design and implementation. Those people include
(but are not limited to) Iavor Diatchki, Aaron Tomb, Adam Wick, Brian
Huffman, Dylan McNamee, Joe Kiniry, John Launchbury, Matt Sottile,
Adam Foltzer, Joe Hendrix, Trevor Elliott, Lee Pike, Mark Tullsen,
Levent Erkök, David Lazar, Joel Stanley, Jeff Lewis, Andy Gill, Edward
Yang, Ledah Casburn, Jim Teisher, Sigbjørn Finne, Mark Shields, Philip
Weaver, Magnus Carlsson, Fergus Henderson, Joe Hurd, Thomas Nordin,
John Matthews and Sally Browning. In addition, much of the work on
Cryptol has been funded by, and lots of design input was provided by
the team at the
[NSA's Trusted Systems Research Group](http://www.nsa.gov/research/ia_research/),
including Brad Martin, Frank Taylor and Sean Weaver.