Cryptol, version 2
This version of Cryptol is (C) 2013-2020 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 Laboratory for Advanced Cybersecurity Research 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
: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
both as tarballs and as
.msi installer packages which place a shortcut
to the Cryptol interpreter in the Start menu.
On Mac OS X, Cryptol is also available via
Homebrew. Simply run
brew update && brew install cryptol
to get the latest stable version.
Cryptol currently uses Microsoft Research's Z3 SMT
solver by default to solve constraints
during type checking, and as the default solver for the
:prove commands. Cryptol generally requires the most recent version
of Z3, but you can see the specific version tested in CI by looking for
Z3_VERSION setting in this
You can download Z3 binaries for a variety of platforms from their releases page. If you install Cryptol using Homebrew, the appropriate version of Z3 will be installed automatically. If you're using Linux, the package manager for your distribution may include Z3, as well, though sometimes the available versions are somewhat old.
After installation, make sure that
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
x64 version of Z3.
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:
- macOS 10.15, 64-bit
- Ubuntu 18.04, 64-bit
- Windows Server 2019, 64-bit
Cryptol is regularly built and tested with the three most recent versions of GHC, which at the time of this writing are 8.6.5, 8.8.4, and 8.10.2. The easiest way to install an approporiate version of GHC is with ghcup.
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:
You'll also need Z3 installed when running Cryptol.
After a fresh checkout of cryptol, be sure to initialize its git submodules:
git submodule update --init
Then, from the Cryptol source directory, run:
This will build Cryptol in place. From there, there are additional targets:
./cry run: run Cryptol in the current directory
./cry test: run the regression test suite
If you run
cabal v2-install --installdir=DIR in your source directory
after running one of the above
./cry command, you will end up with a
Cryptol can use several external files to control its operation. Normally, the build process embeds these files into the executable. However, these embedded files can be overwritten with local copies in two ways:
Copy the contents of the
CRYPTOLPATHenvironment variable to name some other directory that contains the files from the
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.
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 email@example.com.
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, send along pull requests and we'll be happy to incorporate your changes.
/cryptol: Haskell sources for the front-end
cryptolexecutable 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
cryptollibrary (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
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
For a large collection of Cryptol examples, see the cryptol-specs repository.
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. See more information on the SAW website.
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
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) Aaron Tomb, Adam Foltzer, Adam Wick, Alexander Bakst, Andrew Kent, Andrei Stefanescu, Andrey Chudnov, Andy Gill, Benjamin Barenblat, Ben Jones, Ben Selfridge, Brett Boston, Brian Huffman, Brian Ledger, Chris Phifer, Daniel Wagner, David Thrane Christiansen, David Lazar, Dylan McNamee, Eddy Westbrook, Edward Yang, Eric Mertens, Eric Mullen, Fergus Henderson, Iavor Diatchki, Jared Weakly, Jeff Lewis, Jim Teisher, Joe Hendrix, Joe Hurd, Joe Kiniry, Joel Stanley, Joey Dodds, John Launchbury, John Matthews, Jonathan Daugherty, Kenneth Foner, Kevin Quick, Kyle Carter, Ledah Casburn, Lee Pike, Levent Erkök, Lisanna Dettwyler, Magnus Carlsson, Mark Shields, Mark Tullsen, Matt Sottile, Nathan Collins, Philip Weaver, Robert Dockins, Ryan Scott, Sally Browning, Sam Anklesaria, Sigbjørn Finne, Stephen Magill, Thomas Nordin, Trevor Elliott, and Tristan Ravitch.
Much of the work on Cryptol has been funded by, and lots of design input was provided by, the team at the NSA's Laboratory for Advanced Cybersecurity Research, including Brad Martin, Frank Taylor, and Sean Weaver.
Portions of Cryptol are also based upon work supported by the Office of Naval Research under Contract No. N68335-17-C-0452. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Office of Naval Research.