REUNION

REUNION: rendezvous unobservability

This is the reference implementation of the REUNION cryptographic redezvous protocol.

What is REUNION?

REUNION is a privacy preserving transitionally post-quantum cryptographic protocol for rendezvous between two or more participants. With the use of an arbitrary shared passphrase and an agreed upon location or communications medium, two or more participants may exchange a message, usually contact information such as addresses or public keys.

Status of `reunion` implementing REUNION

This is pre-release software, under active development.

How to use REUNION?

It may be used on a local-area network with multicast with reunion-on-an-ethernet or experimentally with reunion-client for use with a reunion-server.

Using REUNION on an ethernet

After installing the Python reunion module it is possible to run purpose built specific commands for the specific usecase that is interesting:

$ reunion-on-an-ethernet --help
Usage: reunion-on-an-ethernet [OPTIONS]

  This implements REUNION on an ethernet.

  If you run it with no arguments, you will be prompted for a passphrase and
  message.

Options:
  -I, --interval INTEGER  Interval at which to start new sessions  [default:
                          60]
  --multicast-group TEXT  [default: 224.3.29.71]
  --bind-addr TEXT        [default: 0.0.0.0]
  --port INTEGER          [default: 9005]
  --reveal-once           Only reveal the message to the first person with the
                          correct passphrase
  --passphrase TEXT       The passphrase
  --message TEXT          The message
  --help                  Show this message and exit.

Using REUNION on a Single Point of Failure (SPOF)

Using reunion outside of a local-area network is possible. We have implemented a web server in reunion-server. The reunion-server is a location where reunion clients may send and receive messsages to run the REUNION protocol.

The reunion-server program provides an HTTP interface which by design is bound only to localhost by default:

$ reunion-server
mode http
 * Serving Flask app 'reunion.server'
 * Debug mode: off
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on http://127.0.0.1:5000
Press CTRL+C to quit

The reunion-client client program connects to a reunion-server and performs REUNION protocol runs until it is manually stopped:

$ reunion-client --msg 'hello world' --passphrase 'I am a jelly donut'

ReunionSession API

The reunion library provides an API for Python developers to integrate the REUNION protcol into their applications.

The reunion.session python module provides a sans IO implementation of the cryptographic protocol which applications can use. So far, reunion.multicast is the only user of this module.

Notes

There is no replay protection here. In the ReunionSession API, replays of the same t2 to the same t1 should always produce the same t3, regardless of if it is a dummy. Applications are currently responsible for implementing replay protection if they desire it.
Deviating slightly from the algorithm in the paper, we introduce a new value dummy_seed which is used with an Hkdf to produce dummy t3 messages. REUNION as described in the paper requires replay protection to maintain unobservability, as its dummy t3s are specified to be random while it's legitimate t3s are deterministic.
Different T2 messages from the same T1 will produce different T3s. The latest T2 received from a given T1 is used when computing the decryption key for its incoming T3 messages.
The size of the payload is not specified here. Applications may implement their own requirement that T1 messages be a fixed size, but the ReunionSession API does not require them to do so.

Setting up REUNION for development

We recommend using a Python virtual environment and installing the library with pip in editable mode:

python -m venv venv
source venv/bin/activate
pip install -e .

Running the tests

Run the test suite with pytest:

pytest -v

Building a Debian package

Generate a Debian package for local use:

fakeroot debian/rules build binary

ioerror/reunion