An easy to use, easy to deploy crypto library
Clone or download


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.


The manual can be found at, 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.

Unless you cloned the git repository, there is a html version in doc/html/, that you can regenerate by executing the doc/ script. This requires mandoc.


The easiest way to use Monocypher is to include src/monocypher.h and src/monocypher.c directly into your project. They compile as C99, C11, C++98, C++11, C++14, and C++17.

Alternatively, you can run make, then grab lib/libmonocypher.a or lib/ If you're running a UNIX system, you can even install Monocypher (you need to be root):

$ 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

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/
$ tests/

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/
$ tests/

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

$ tests/
$ tests/formal-analysis/*.c

(Note: is part of TIS. If it is not in your path, adjust the command accordingly.)

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"


For simplicity, compactness, and performance reasons, Monocypher signatures default to EdDSA with curve25519 and Blake2b. This is different from the more mainstream Ed25519, which uses SHA-512 instead.

If you need Ed25519 compatibility, you must do the following:

  • Compile Monocypher.c with option -DED25519_SHA512.
  • Link the final program with a suitable SHA-512 implementation. You can use the sha512.c and sha512.h files provided in src/optional.

Note that even though the default hash (Blake2b) is not "standard", you can still upgrade to faster implementations if you really need to. The Donna implementations of ed25519 for instance can use a custom hash —one test does just that.

Contributor notes

If you just cloned the GitHub repository, you will 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/ script. You will need mandoc.

To generate a tarball, simply type make tarball. It will make a tarball with a name that matches the current version (as written in, in the current directory.