Katzen

Katzen is a new private instant messaging application built using the Katzenpost mixnet project, which is an overlay network that is able to hide communication patterns of individual users from passive network observers. This means that attackers cannot link sending and receiving of messages on the network with any of the participants. Messages between conversation parties are delivered to and read from message queues operated by the mixnet service operators. The legacy simple design maintains a per client queue and is able to see when a client is receiving a message, how often clients receive messages, and when the client is online and checking for their messages. The purpose of this project is to replace the legacy ephemeral message storage system used by Katzen with a replacement that does not link messages with a specific user or conversation, To do this, clients will include a csprng seed as part of the contact creation process that will be used to generate a deterministic sequence of message identifiers between conversation participants; these identifiers will be used by each client to query the ephemeral storage provider for the next message in the conversation. Because polling the storage service adds latency, and this design must check for new messages from each conversation partner, mechanisms to reduce the number of round trips - such as using SURBs as an asynchronous callback upon message delivery on the storage provider will be explored as a means to build a mixnet 'push' service to decrease the total round trip delay in receiving a new message.