mirror of https://git.matrix.org/git/olm.git
115 lines
3.0 KiB
ReStructuredText
115 lines
3.0 KiB
ReStructuredText
Olm
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===
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An implementation of the Double Ratchet cryptographic ratchet described by
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https://github.com/trevp/double_ratchet/wiki, written in C and C++11 and
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exposed as a C API.
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The specification of the Olm ratchet can be found in ``docs/olm.rst`` or
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https://matrix.org/docs/spec/olm.html.
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This library also includes an implementation of the Megolm cryptographic
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ratchet, as specified in ``docs/megolm.rst`` or
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https://matrix.org/docs/spec/megolm.html.
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Building
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--------
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To build olm as a shared library run:
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.. code:: bash
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make
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To run the tests run:
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.. code:: bash
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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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.. code:: bash
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make js
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Release process
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---------------
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.. code:: bash
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# Bump version numbers in ``Makefile`` and ``javascript/package.json``
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# Prepare changelog
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git commit
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make clean
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make test
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make js
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npm pack javascript
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VERSION=x.y.z
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scp olm-$VERSION.tgz packages@ldc-prd-matrix-001:/sites/matrix/packages/npm/olm/
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git tag $VERSION -s
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git push --tags
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It's probably sensible to do the above on a release branch (``release-vx.y.z``
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by convention), and merge back to master once complete.
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Design
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------
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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
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API. As development has progressed, it has become clear that C++ gives little
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advantage, and new functionality is being added in C, with C++ parts being
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rewritten as the need ariases.
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Error Handling
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~~~~~~~~~~~~~~
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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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~~~~~~~~~~~~~~
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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
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platforms since the caller can use whatever cryptographic random number
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generator their platform provides.
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Memory
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~~~~~~
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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
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output and the caller supplies a buffer of the appropriate size.
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Output Encoding
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~~~~~~~~~~~~~~~
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Binary output is encoded as base64 so that languages that prefer unicode
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strings will find it easier to handle the output.
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Dependencies
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~~~~~~~~~~~~
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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
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to compile the library for different architectures.
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What's an olm?
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--------------
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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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------------
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The software may be subject to the U.S. export control laws and regulations
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and by downloading the software the user certifies that he/she/it is
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authorized to do so in accordance with those export control laws and
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regulations.
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