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4.5 KiB

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:
.. code:: bash
To run the tests run:
.. code:: bash
make test
To build the javascript bindings, install emscripten from http://kripken.github.io/emscripten-site/ and then run:
.. code:: bash
make js
To build the android project for Android bindings, run:
.. code:: bash
cd android
./gradlew clean assembleRelease
To build the Xcode workspace for Objective-C bindings, run:
.. code:: bash
cd xcode
pod install
open OLMKit.xcworkspace
To build olm as a static library (which still needs libstdc++ dynamically) run:
.. code:: bash
make static
Release process
First: bump version numbers in ``common.mk``, ``javascript/package.json``,
``OLMKit.podspec``, and ``android/olm-sdk/build.gradle`` (``versionCode``,
``versionName`` and ``version``).
Also, ensure the changelog is up to date, and that everyting is committed to
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.
.. code:: bash
make clean
# build and test C library
make test
# build and test JS wrapper
make js
(cd javascript && npm run test)
npm pack javascript
scp olm-$VERSION.tgz packages@ares.matrix.org:packages/npm/olm/
git tag $VERSION -s
git push --tags
# OLMKit CocoaPod release
# Make sure the version OLMKit.podspec is the same as the git tag
# (this must be checked before git tagging)
pod spec lint OLMKit.podspec --use-libraries --allow-warnings
pod trunk push OLMKit.podspec --use-libraries --allow-warnings
# Check the pod has been successully published with:
pod search OLMKit
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.
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.
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.
Security assessment
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
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/
Bug reports
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.
Legal Notice
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