README.rst

Olm

An implementation of the cryptographic ratchet described by https://github.com/trevp/axolotl/wiki, written in C++11 and exposed as a C API

The specification of the Olm ratchet can be found in docs/olm.rst or https://matrix.org/docs/spec/olm.html

Building

To build olm as a shared library run:

make

To run the tests run:

make test

To build the javascript bindings, install emscripten from http://kripken.github.io/emscripten-site/ and then run:

make js
npm pack javascript  # packages olm.js into olm-x.y.z.tgz

Remember to make a tag after releasing a tarball:

git tag x.y.z
git push --tags

Design

Olm is designed to be easy port to different platforms and to be easy to write bindings for.

It was originally implemented in C++, with a plain-C layer providing the public API. As development has progressed, it has become clear that C++ gives little advantage, and new functionality is being added in C, with C++ parts being rewritten as the need ariases.

Error Handling

All C functions in the API for olm return olm_error() on error. This makes it easy to check for error conditions within the language bindings.

Random Numbers

Olm doesn't generate random numbers itself. Instead the caller must provide the random data. This makes it easier to port the library to different platforms since the caller can use whatever cryptographic random number generator their platform provides.

Memory

Olm avoids calling malloc or allocating memory on the heap itself. Instead the library calculates how much memory will be needed to hold the output and the caller supplies a buffer of the appropriate size.

Output Encoding

Binary output is encoded as base64 so that languages that prefer unicode strings will find it easier to handle the output.