[tor-dev] announcing: txmix, a twisted python mixnet library

dawuud dawuud at riseup.net
Sun Feb 19 21:52:17 UTC 2017

Hi. I'd like to announce txmix, a library for writing mixnets in python.


txmix is GPL3 licensed and currently depends on:
sphinxmixcrypto, Twisted, txtorcon, attrs, eliot
and Tor Project's chutney (for integration tests).

txmix allows you to write mixnets with reduced code complexity and
transport agnosticism... however I've choosen to focus my development
efforts on the Tor onion transport for several reasons, the onion
transport has some properties which the UDP transport does not:

- reliability
- forward secrecy
- NAT penetration

Additionally the Tor anonymity properties are a welcome bonus since
they aren't really overlapping with those of the mixnet, they are
vulnerable to different types of attacks and accomodate for totally
different threat models.

Currently txmix has some integration tests that use chutney to spin up
a local 25 relay tor network; builds a mixnet using onion services
as the transport and then tests functionality by sending and receiving
messages on the mixnet.

future development

- txmix could certainly be used to write various kinds of mixnets,
however, we are missing a PKI. Without some kind of public key
infrastructure how will mix clients learn about mix public keys?

- sphixmixcrypto library needs improvements that would allow us
to specify more message types such as dummy/cover traffic message
and heartbeat messages. These of course are essential for the defense
against certain known active attacks against some mix types.

questions, code review and pull requests welcome.

David Stainton
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