“An especially problematic excision of the political is the marginalization within the cryptographic community of the secure-messaging problem, an instance of which was the problem addressed by David Chaum. Secure-messaging is the most fundamental privacy problem in cryptography: how can parties communicate in such a way that nobody knows who said what. More than a decade after the problem was introduced, Rackoff and Simon would comment on the near-absence of attention being paid to the it.” (Phillip Rogaway, The Moral Character of Cryptographic Work)

Katzenpost Overview

The Katzenpost Free Software Project

Katzenpost is a free software project. We write mix network protocol libraries. What is a mix network? It is an anonymous communications system… however the word anonymous is problematic because some government authorities equate anonymity with terrorism. We prefer to instead call it “network security” because you can feel more secure when you communicate using traffic analysis resistant communications protocols.

However we realize we cannot simply write a mix network and core protocol libraries and expect people to use them. Therefore we are working towards a demonstration encrypted chat client which will communicate over our mix network. In the spirit of pond this new chat client will use PANDA (Phrase Automated Nym Discovery Authentication) for the key exchange and the Signal Double Ratchet for the end to end encryption.

Traffic analysis helps governments, corporations and Internet service providers learn more information about the communication even if it is encrypted. The goal of protecting the confidentiality of messages is in fact an orthogonal concern to that of resisting traffic analysis. In particular we are interested in developing mix network based communications systems that can be used by everyone to hide these kinds of communications metadata:

  • geographic location

  • message sender

  • message receiver

  • message sent time

  • message receive time

  • message size

  • ordering of messages

  • frequency of sent messages

  • frequency of received messages

However we also consider bad actors within the mix network as well as active attackers. Our threat model is very clearly articulated in the “Loopix Anonymity System” however at the end of each of our design specification documents we have not only a security section but an anonymity considersations section as well.

There are many message oriented applications and protocols that could benefit from using our mix network. For example our mix network is not only good for chat clients but also other types of applications:

  • transporting interactions between CRDTs

  • transporting interactions to DHTs

  • database transaction anonymization

  • ‘crypto currency’ anonymization, especially Zcash which has shielded transactions which are particularly well suited to being used with a mix network transport protocol

For further discussion regarding Zcash usage with Katzenpost please see: Using Zcash with Katzenpost.


Supported by

European Union flag

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Grant Agreement No 653497, Privacy and Accountability in Networks via Optimized Randomized Mix-nets (Panoramix)” and is part of the PANORAMIX Framework.