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# Olm
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An implementation of the Double Ratchet cryptographic ratchet described by
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https://whispersystems.org/docs/specifications/doubleratchet/, written in C and
C++11 and exposed as a C API.
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The specification of the Olm ratchet can be found in [docs/olm.md](docs/olm.md).
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This library also includes an implementation of the Megolm cryptographic
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ratchet, as specified in [docs/megolm.md](docs/megolm.md).
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## Building
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To build olm as a shared library run either:

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```bash
cmake . -Bbuild
cmake --build build
```
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or:
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```bash
make
```
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Using cmake is the preferred method for building the shared library; the
Makefile may be removed in the future.

To run the tests when using cmake, run:

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```bash
cd build/tests
ctest .
```
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To run the tests when using make, run:
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```bash
make test
```
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To build the JavaScript bindings, install emscripten from http://kripken.github.io/emscripten-site/ and then run:
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```bash
make js
```
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Note that if you run emscripten in a docker container, you need to pass through
the EMCC_CLOSURE_ARGS environment variable.

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To build the android project for Android bindings, run:

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```bash
cd android
./gradlew clean assembleRelease
```
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To build the Xcode workspace for Objective-C bindings, run:

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```bash
cd xcode
pod install
open OLMKit.xcworkspace
```
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To build the Python bindings, first build olm as a shared library as above, and
then run:

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```bash
cd python
make
```
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to make both the Python 2 and Python 3 bindings.  To make only one version, use
``make olm-python2`` or ``make olm-python3`` instead of just ``make``.

To build olm as a static library (which still needs libstdc++ dynamically) run
either:

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```bash
cmake . -Bbuild -DBUILD_SHARED_LIBS=NO
cmake --build build
```
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or
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```bash
make static
```
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The library can also be used as a dependency with CMake using:

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```cmake
find_package(Olm::Olm REQUIRED)
target_link_libraries(my_exe Olm::Olm)
```
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## Bindings

libolm can be used in different environments using bindings. In addition to the
JavaScript, Python, Java (Android), and Objective-C bindings included in this
repository, some bindings are (in alphabetical order):

- [dart-olm](https://gitlab.com/famedly/libraries/dart-olm) (AGPLv3) Dart bindings
- [Dhole/go-olm](https://github.com/Dhole/go-olm) (Apache-2.0) Go bindings
- [libQtOlm](https://gitlab.com/b0/libqtolm/) (GPLv3) Qt bindings
- [matrix-kt](https://github.com/Dominaezzz/matrix-kt) (Apache-2.0) Kotlin
  library for Matrix, including Olm methods
- [maunium.net/go/mautrix/crypto/olm](https://github.com/tulir/mautrix-go/tree/master/crypto/olm)
  (Apache-2.0) fork of Dhole/go-olm
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- [nim-olm](https://gitea.com/BarrOff/nim-olm) (MIT) Nim bindings
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- [olm-sys](https://gitlab.gnome.org/BrainBlasted/olm-sys) (Apache-2.0) Rust
  bindings

Note that bindings may have a different license from libolm.

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## Release process
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First: bump version numbers in ``common.mk``, ``CMakeLists.txt``,
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``javascript/package.json``, ``python/olm/__version__.py``, ``OLMKit.podspec``,
and ``android/olm-sdk/build.gradle`` (``versionCode``, ``versionName`` and
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``version``).
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Also, ensure the changelog is up to date, and that everything is committed to
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git.
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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.

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```bash
make clean
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# build and test C library
make test
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# build and test JS wrapper
make js
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(cd javascript && npm run test && npm pack javascript)
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VERSION=x.y.z
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gpg -b -a -u F75FDC22C1DE8453 javascript/olm-$VERSION.tgz
scp javascript/olm-$VERSION.tgz packages@ares.matrix.org:packages/npm/olm/
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git tag $VERSION -s
git push --tags
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# 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
```
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## Design
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Olm is designed to be easy port to different platforms and to be easy
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to write bindings for.

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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.

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

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### Random Numbers
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Olm doesn't generate random numbers itself. Instead the caller must
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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.

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

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

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### Dependencies
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Olm uses pure C implementations of the cryptographic primitives used by
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the ratchet. While this decreases the performance it makes it much easier
to compile the library for different architectures.
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## Contributing
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Please see [CONTRIBUTING.md](CONTRIBUTING.md) when making contributions to the library.

## Security assessment
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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/

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## Bug reports

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Please file bug reports at https://github.com/matrix-org/olm/issues

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## What's an olm?
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It's a really cool species of European troglodytic salamander.
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http://www.postojnska-jama.eu/en/come-and-visit-us/vivarium-proteus/
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## Legal Notice
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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.