A signaling channel is a transport that can be public, because the collateral damage for censors to block it, but too slow or too expensive to move real Tor traffic over it. We use those to bootstrap other protocols like moat or snowflake
- domain fronting
- AMP cache
- AWS SQS queue
- dnstt
- Google Pub/Sub
- Google App Script
- PassKeys servers
- ECH on cloud providers
- S3
- Push notifications
- Google docs
- TURN servers
domain fronting
There are less and less cloud providers allowing it.
AMP cache
- tpo/anti-censorship/pluggable-transports/snowflake!50 (closed)
- https://www.bamsoftware.com/papers/snowflake/#p21
AWS SQS queue
- tpo/anti-censorship/pluggable-transports/snowflake!214 (closed)
- https://www.bamsoftware.com/papers/snowflake/#p22
dnstt
https://www.bamsoftware.com/software/dnstt/
Google Pub/Sub
https://www.petsymposium.org/foci/2024/foci-2024-0010.php
https://github.com/AfonsoVilalonga/PubSub-Rendezvous
Google App Script
https://github.com/fortuna/OutlineDistribution
PassKeys servers
Using passkeys servers: https://fidoalliance.org/passkeys/
An example project: https://github.com/c-skills/passport
ECH on cloud providers
Cloudflare seems to support it already: https://github.com/net4people/bbs/issues/393
S3
https://www.petsymposium.org/foci/2024/foci-2024-0011.pdf
Push notifications
https://gitlab.torproject.org/tpo/anti-censorship/team/-/wikis/Signaling-Channels/Push-Notifications
Google docs
https://web.archive.org/web/20230330055859/https://easrng.blogspot.com/2022/03/get-tor-bridges-with-nothing-but.html
https://developers.cloudflare.com/1.1.1.1/other-ways-to-use-1.1.1.1/dns-in-google-sheets/
bridgedb#40047
TURN servers
https://www.petsymposium.org/foci/2025/foci-2025-0003.php
In general TURN services are paid per traffic.