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Python implementation of the Axolotl ratchet protocol

Project description


The Axolotl ratchet is a protocol (similar to OTR) that provides for perfect forward secrecy in (a)synchronous communications. It uses triple Diffie-Hellman for authentication and ECDHE for perfect forward secrecy. The protocol is lighter and more robust than the OTR protocol - providing better forward and future secrecy, as well as deniability.

The protocol was developed by Trevor Perrin and Moxie Marlinspike. Its chief use currently is in the Whisper Systems TextSecure SMS package.

A nice writeup of the protocol is on the Whisper Systems Blog. You can find the most recent specification of the protocol here.

Installation instructions

If you use pip, install pyaxo with:

sudo pip install pyaxo

pyaxo will be ready for use!

If you do not use pip, first make sure that you have the following:

sudo apt-get install python-dev

You will have to install the curve25519-donna package manually, since pyaxo requires it for doing the ECDHE calculations. It can be installed by:

git clone
cd curve25519-donna
sudo python install

pyaxo also uses python-gnupg and passlib, and if you have setuptools installed, these packages will be downloaded and installed automatically. You may need some additional python modules as well. Check the imports list.

Finally, from pyaxo’s source folder, install with:

sudo python install


There are several examples showing usage. There are also encrypt_pipe() and decrypt_pipe() methods for use in certain applications. I haven’t put together an example using them yet, but it should be straightforward.

Bugs, etc. should be reported to the pyaxo github issues page.

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