WebRTC Pluggable Transport
Switch branches/tags
Nothing to show
Clone or download
David Fifield
David Fifield Fix text-shadow CSS.
The semicolons made it look like the end of a declaration. I got these
errors in the Firefox console:

Expected declaration but found ‘1px’.  Skipped to next declaration. 1 embed.html:29:17
Expected declaration but found ‘-1px’.  Skipped to next declaration. 1 embed.html:30:17
Latest commit fd9efa1 Apr 18, 2018



Build Status

Pluggable Transport using WebRTC, inspired by Flashproxy.


  • Transport: Successfully connects using WebRTC.
  • Rendezvous: HTTP signaling (with optional domain fronting) to the Broker arranges peer-to-peer connections with multitude of volunteer "snowflakes".
  • Client multiplexes remote snowflakes.
  • Can browse using Tor over Snowflake.
  • Reproducible build with TBB.

Table of Contents


cd client/
go get
go build
tor -f torrc

This should start the client plugin, bootstrapping to 100% using WebRTC.




More Info

Tor can plug in the Snowflake client via a correctly configured torrc. For example:

ClientTransportPlugin snowflake exec ./client \
-url https://snowflake-reg-test.appspot.com/ \
-front www.google.com \
-ice stun:stun.l.google.com:19302
-max 3

The flags -url and -front allow the Snowflake client to speak to the Broker, in order to get connected with some volunteer's browser proxy. -ice is a comma-separated list of ICE servers, which are required for NAT traversal.

For logging, run tail -F snowflake.log in a second terminal.

You can modify the torrc to use your own broker, or remove the options entirely which will default to the old copy paste method (see torrc-manual):

ClientTransportPlugin snowflake exec ./client --meek


This describes how to build the in-browser snowflake. For the client, see Usage, above.

The client will only work if there are browser snowflakes available. To run your own:

cd proxy/
cake build

(Type cake by itself to see possible commands)

Then, start a local http server in the proxy/build/ in any way you like. For instance:

cd build/
python -m http.server

Then, open a browser tab to to view the debug-console of the snowflake., So long as that tab is open, you are an ephemeral Tor bridge.


Q: How does it work?

In the Tor use-case:

  1. Volunteers visit websites which host the "snowflake" proxy. (just like flashproxy)
  2. Tor clients automatically find available browser proxies via the Broker (the domain fronted signaling channel).
  3. Tor client and browser proxy establish a WebRTC peer connection.
  4. Proxy connects to some relay.
  5. Tor occurs.

More detailed information about how clients, snowflake proxies, and the Broker fit together on the way...

Q: What are the benefits of this PT compared with other PTs?

Snowflake combines the advantages of flashproxy and meek. Primarily:

  • It has the convenience of Meek, but can support magnitudes more users with negligible CDN costs. (Domain fronting is only used for brief signalling / NAT-piercing to setup the P2P WebRTC DataChannels which handle the actual traffic.)

  • Arbitrarily high numbers of volunteer proxies are possible like in flashproxy, but NATs are no longer a usability barrier - no need for manual port forwarding!

Q: Why is this called Snowflake?

It utilizes the "ICE" negotiation via WebRTC, and also involves a great abundance of ephemeral and short-lived (and special!) volunteer proxies...


-- Testing with Standalone Proxy --
cd proxy-go
go build
-- Testing Copy-Paste Via Browser Proxy --

Open a browser proxy, passing the manual parameter; e.g.,

Open up three terminals for the client:

A: tor -f torrc-manual SOCKSPort auto

B: cat > signal

C: tail -F snowflake.log

Then, in the browser proxy:

  • Look for the offer in terminal C; copy and paste it into the browser.
  • Copy and paste the answer generated in the browser back to terminal B.
  • Once WebRTC successfully connects, the browser terminal should turn green. Shortly after, the tor client should bootstrap to 100%.
-- Testing directly via WebRTC Server --

See server-webrtc/README.md for information on connecting directly to a WebRTC server transport plugin, bypassing the Broker and browser proxy.

More documentation on the way.

Also available at: torproject.org/pluggable-transports/snowflake