May 4, 2019
Katzenpost Monthly News Update¶
The last few weeks have been very busy. I now have the basic working prototype implementation of a new Katzenpost messaging system. This new system has mutual location hiding properties for communication partners because recipients retreive their messages from a remote spool using a Sphinx SURB based protocol. [SPHINX] [SPHINXSPEC]
Naming things is tricky. I had to call it something: https://github.com/katzenpost/catshadow
This messaging system is inspired by agl’s pond, obviously. See agl’s pond here: https://github.com/agl/pond
I forked agl’s Double Ratchet from pond: https://github.com/katzenpost/doubleratchet
Also forked agl’s PANDA: https://github.com/katzenpost/panda
Communication partners use a remote spool service which is now, memspool but later it will be a replicating CRDT: https://github.com/katzenpost/memspool
In order to exchange double ratchet keys and spool identities to form a bidirectional cryptographic channel, clients make use of the PANDA service. That is to say, PANDA (Phrase Automated Nym Discovery Authentication) is just another mixnet service like the memspool service mentioned above.
The user interface I wrote is a CLI terminal interface and it really kind of sucks. I’m feeling rather inspired by Special’s golang Ricochet. The UI and the backend are two separate processes and communicate by unix domain socket. Cool. Maybe I should do a similar construction that way someone else can later write a crazy C++ Gtk UI for this thing. Although I suspect this strategy doesn’t work well with Android. Unclear. At any rate, catshadow is crash fault tolerant, I hope. It is also internally way more simple than mailproxy and doesn’t use database transactions or anything like that. State is persisted to disk in an encrypted statefile… passphrase, argon2, nacl secretbox of course.
Anyway describing this whole thing is basically a paper worth of words which I shall attempt to articulate later. The overall strategy for Katzenpost should be for this client to merely serve as a demonstration. Whereas it would be far better to help another software project integrate with Katzenpost. Projects such as Briar and Wire come to mind. That having been said, I’d like to soon start a volunteer operated Katzenpost mix network so that we have some real infrastructure that allows us to start using catshadow to send each other encrypted messages. The amount of metadata we leak onto the network will depend on how many people use the system, number of mixes and of course how it is tuned. Since tuning is currently an unsolved problem, it’s all just a fun game anyway.
OK folks that’s all for now. I am not sure exactly what the next steps should be and I’m planning on deliberating while I discuss it with my colleagues and advisors. Either I will start a demo mixnet all on one machine that we can use to try out catshadow or I will attempt to instigate a volunteer operated mixnet. Things will get very cool once we have multiple applications that can use the mixnet. :)
Danezis, G., Goldberg, I., “Sphinx: A Compact and Provably Secure Mix Format”, DOI 10.1109/SP.2009.15, May 2009, <https://cypherpunks.ca/~iang/pubs/Sphinx_Oakland09.pdf>.
Angel, Y., Danezis, G., Diaz, C., Piotrowska, A., Stainton, D., “Sphinx Mix Network Cryptographic Packet Format Specification” July 2017, <https://github.com/katzenpost/docs/blob/master/specs/sphinx.rst>.