Monocypher

Monocypher is an easy to use, easy to deploy, auditable crypto library written in portable C. It approaches the size of TweetNaCl and the speed of Libsodium.

Official site.
Official releases.

Manual

The manual can be found at https://monocypher.org/manual/, and in the doc/ folder.

The doc/man/ folder contains the man pages. You can install them in your system by running make install-doc. Official releases also have a doc/html/ folder with an html version.

Installation

Option 1: grab the sources

The easiest way to use Monocypher is to include src/monocypher.h and src/monocypher.c directly into your project. They compile as C (since C99) and C++ (since C++98).

Option 2: grab the library

Run make, then grab the src/monocypher.h header and either the lib/libmonocypher.a or lib/libmonocypher.so library. The default compiler is gcc -std=gnu99, and the default flags are -pedantic -Wall -Wextra -O3 -march=native. If they don't work on your platform, you can change them like this:

$ make CC="clang -std=c99" CFLAGS="-O2"

Option 3: install it on your system

The following should work on most UNIX systems:

$ make install

This will install Monocypher in /usr/local/ by default. Libraries will go to /usr/local/lib/, the header in /usr/local/include/, and the man pages in /usr/local/share/man/man3. You can change those defaults with the PREFIX and DESTDIR variables thus:

$ make install PREFIX="/opt"

Once installed, you can use pkg-config to compile and link your program. For instance, if you have a one file C project that uses Monocypher, you can compile it thus:

$ gcc -o myProgram myProgram.c        \
    $(pkg-config monocypher --cflags) \
    $(pkg-config monocypher --libs)

The cflags line gives the include path for monocypher.h, and the libs line provides the link path and option required to find libmonocypher.a (or libmonocypher.so).

Test suite

$ make test

It should display a nice printout of all the tests, all starting with "OK". If you see "FAILURE" anywhere, something has gone very wrong somewhere.

Do not use Monocypher without running those tests at least once.

The same test suite can be run under Clang sanitisers and Valgrind, and be checked for code coverage:

$ tests/test.sh
$ tests/coverage.sh

Serious auditing

The code may be analysed more formally with Frama-c and the TIS interpreter. To analyse the code with Frama-c, run:

$ tests/formal-analysis.sh
$ tests/frama-c.sh

This will have Frama-c parse, and analyse the code, then launch a GUI. You must have Frama-c installed. See frama-c.sh for the recommended settings. To run the code under the TIS interpreter, run

$ tests/formal-analysis.sh
$ tis-interpreter.sh --cc -Dvolatile= tests/formal-analysis/*.c

Notes:

• tis-interpreter.sh is part of TIS. If it is not in your path, adjust the command accordingly.

• The TIS interpreter sometimes fails to evaluate correct programs when they use the volatile keyword (which is only used as an attempt to prevent dead store elimination for memory wipes). The -cc -Dvolatile= option works around that bug by ignoring volatile altogether.

Speed benchmark

$ make speed

This will give you an idea how fast Monocypher is on your machine. Make sure you run it on the target platform if performance is a concern. If Monocypher is too slow, try Libsodium or NaCl. If you're not sure, you can always switch later.

Note: the speed benchmark currently requires the POSIX clock_gettime() function.

There are similar benchmarks for Libsodium and TweetNaCl:

$ make speed-sodium
$ make speed-tweetnacl

You can also adjust the optimisation options for Monocypher and TweetNaCl (the default is -O3 march=native):

$ make speed           CFLAGS="-O2"
$ make speed-tweetnacl CFLAGS="-O2"

Customisation

Monocypher has two preprocessor flags: ED25519_SHA512 and BLAKE2_NO_UNROLLING, which are activated by compiling monocypher.c with the options -DED25519_SHA512 and -DBLAKE2_NO_UNROLLING respectively.

The -DED25519_SHA512 option is a compatibility feature for public key signatures. The default is EdDSA with Curve25519 and Blake2b. Activating the option replaces it by Ed25519 (EdDSA with Curve25519 and SHA-512). When this option is activated, you will need to link the final program with a suitable SHA-512 implementation. You can use the sha512.c and sha512.h files provided in src/optional. The makefile does this linking automatically whenever the $CFLAGS variable contains the -DED25519_SHA512 option. For instance:

$ make CFLAGS="-O2 -DED25519_SHA512"

The -DBLAKE2_NO_UNROLLING option is a performance tweak. By default, Monocypher unrolls the Blake2b inner loop, because doing so is over 25% faster on modern processors. Some embedded processors however, run the unrolled loop slower (possibly because of the cost of fetching 5KB of additional code). If you're using an embedded platform, try this option. The binary will be about 5KB smaller, and in some cases faster.

Contributor notes

If you are reading this, you cloned the GitHub repository. You miss a couple files that ship with the tarball releases:

• The test/vectors.h header. Generating it requires Libsodium. Go to test/gen/, then run make.
• The html version of the manual, generated by the doc/man2html.sh script. You will need mandoc.

To generate a tarball, simply type make dist. It will make a tarball with a name that matches the current version (using git describe), in the current directory.