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This is a python port of [libsignal-protocol-java](https://github.com/WhisperSystems/libaxolotl-android) originally written by [Moxie Marlinspike](https://github.com/moxie0)
Overview from original author's:
> This is a ratcheting forward secrecy protocol that works in synchronous and asynchronous messaging environments.
# Installation
The library has some dependencies which are automatically pulled and installed if you use the instructions below for your OS
- [protobuf 3.0+](https://github.com/google/protobuf/)
- [cryptography](https://cryptography.io)
- [python-axolotl-curve25519](https://github.com/tgalal/python-axolotl-curve25519)
## Linux
You need to have python headers installed, usually through installing a package called `python-dev`, then as superuser run:
```
python setup.py install
```
## Windows
- Install [mingw](http://www.mingw.org/) compiler
- Add mingw to your PATH
- In PYTHONPATH\Lib\distutils create a file called distutils.cfg and add these lines:
```
[build]
compiler=mingw32
```
- Install gcc: ```mingw-get.exe install gcc```
- Install [zlib](http://www.zlib.net/)
- ```python setup.py install```
# Usage
This python port is done in an almost 1:1 mapping to the original java code. Therefore any original documentation for the java code can be easily mapped and used with this python port.
## Install time
At install time, a libaxolotl client needs to generate its identity keys, registration id, and
prekeys.
```python
identityKeyPair = KeyHelper.generateIdentityKeyPair()
registrationId = KeyHelper.generateRegistrationId()
preKeys = KeyHelper.generatePreKeys(startId, 100)
lastResortKey = KeyHelper.generateLastResortKey()
signedPreKey = KeyHelper.generateSignedPreKey(identityKeyPair, 5)
#Store identityKeyPair somewhere durable and safe.
#Store registrationId somewhere durable and safe.
#Store preKeys in PreKeyStore.
#Store signed prekey in SignedPreKeyStore.
```
## Building a session
A libaxolotl client needs to implement four interfaces: IdentityKeyStore, PreKeyStore,
SignedPreKeyStore, and SessionStore. These will manage loading and storing of identity,
prekeys, signed prekeys, and session state.
Once those are implemented, building a session is fairly straightforward:
```python
sessionStore = MySessionStore()
preKeyStore = MyPreKeyStore()
signedPreKeyStore = MySignedPreKeyStore()
identityStore = MyIdentityKeyStore()
# Instantiate a SessionBuilder for a remote recipientId + deviceId tuple.
sessionBuilder = SessionBuilder(sessionStore, preKeyStore, signedPreKeyStore,
identityStore, recipientId, deviceId)
# Build a session with a PreKey retrieved from the server.
sessionBuilder.process(retrievedPreKey)
sessionCipher = SessionCipher(sessionStore, recipientId, deviceId)
message = sessionCipher.encrypt("Hello world!")
deliver(message.serialize())
```
# Examples
python-axolotl is actively used in [yowsup](https://github.com/tgalal/yowsup) to support E2E encryption of WhatsApp
# License
Licensed under the GPLv3: http://www.gnu.org/licenses/gpl-3.0.html
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