Cryptol, version 2

This version of Cryptol is (C) 2013-2014 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. 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. 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.

Getting CVC4

Cryptol currently depends on the CVC4 SMT solver to solve constraints during type checking, and as the default solver for the :sat and :prove commands. You can download CVC4 binaries for a variety of platforms from their download page.

Building Cryptol From Source

In addition to the binaries, the Cryptol source is available publicly on GitHub.

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 10.9 64-bit
• CentOS 5 32/64-bit
• CentOS 6 32/64-bit
• Windows XP 32-bit

Prerequisites

Cryptol is developed using GHC 7.6.3 and cabal-install 1.18. While you can install these independently, the easiest way to get the correct versions is to:

1. Install Haskell Platform 2013.2.0.0

   Mac Users: the current version of the Haskell Platform has some incompatibilities with Mac OS X 10.9; it is easier to install GHC, cabal-install, alex, and happy from MacPorts or Homebrew.

2. Run cabal update

3. Run cabal install cabal-install

4. Add cabal-install's binary path to your PATH variable (usually ~/.cabal/bin)

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)
• ncurses

You'll also need CVC4 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 test: run the regression test suite (note: 4 failures is expected)
• make docs: build the Cryptol documentation (requires pandoc and TeX Live)
• 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 3.7, which must be installed separately.

Installing Cryptol

Aside from the docs target, these will leave you with a Cryptol binary at .cabal-sandbox/bin/cryptol in your source directory. You can either use that binary directly, or use the results of tarball or dist to install Cryptol in a location of your choice.

Checking your Installation

Run Cryptol, and at the prompt type:

Cryptol> :prove True

If Cryptol responds

Q.E.D.

then Cryptol is installed correctly. If it prints something like

*** An error occurred.
***  Unable to locate executable for cvc4
***  Executable specified: "cvc4"

then make sure you've installed CVC4, and that the binary is on your PATH.

As noted above, make test currently results in four failures. An issue has been filed on GitHub for each of them.

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.

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, 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. These are tasks which should be straightforward to implement. Make a fork of this GitHub repository and 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
• /notebook: Experimental Cryptol IPython Notebook implementation
• /sbv: Haskell sources for the sbv library, derived from Levent Erkok's sbv library (see /sbv/LICENSE)
• /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, including Brad Martin, Frank Taylor and Sean Weaver.