An implementation of the Double Ratchet cryptographic ratchet described by https://whispersystems.org/docs/specifications/doubleratchet/, written in C and C++11 and exposed as a C API.
The specification of the Olm ratchet can be found in docs/olm.rst.
This library also includes an implementation of the Megolm cryptographic ratchet, as specified in docs/megolm.rst.
To build olm as a shared library run:
To run the tests run:
To build the android project for Android bindings, run:
cd android ./gradlew clean assembleRelease
To build the Xcode workspace for Objective-C bindings, run:
cd xcode pod install open OLMKit.xcworkspace
To build olm as a static library (which still needs libstdc++ dynamically) run:
Also, ensure the changelog is up to date, and that everyting is committed to git.
It's probably sensible to do the above on a release branch (release-vx.y.z by convention), and merge back to master once the release is complete.
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.
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.
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.
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.
Binary output is encoded as base64 so that languages that prefer unicode strings will find it easier to handle the output.
Olm uses pure C implementations of the cryptographic primitives used by the ratchet. While this decreases the performance it makes it much easier to compile the library for different architectures.
Please see CONTRIBUTING.rst when making contributions to the library.
Olm 1.3.0 was independently assessed by NCC Group's Cryptography Services Practive in September 2016 to check for security issues: you can read all about it at https://www.nccgroup.trust/us/our-research/matrix-olm-cryptographic-review/ and https://matrix.org/blog/2016/11/21/matrixs-olm-end-to-end-encryption-security-assessment-released-and-implemented-cross-platform-on-riot-at-last/
Please file bug reports at https://github.com/matrix-org/olm/issues
What's an olm?
It's a really cool species of European troglodytic salamander. http://www.postojnska-jama.eu/en/come-and-visit-us/vivarium-proteus/
The software may be subject to the U.S. export control laws and regulations and by downloading the software the user certifies that he/she/it is authorized to do so in accordance with those export control laws and regulations.