❄️ Snowflake Generalized

Censorship circumvention software like Snowflake, but faster thanks to not using Tor.

Acts as a TCP or UDP tunnel between the user (client) and the server, much like ssh -L.

This, in turn, allows the client to access any blocked TCP / UDP service, such as a SOCKS proxy or your favorite (but blocked) VPN service provider.

This project is based on a fork of Snowflake. The difference between the fork and the original can be found here. In summary, the changes are:

• Allow clients to ask proxies to connect to any host they choose.
• Add a lot of hardening features (which are needed because of the previous bullet point). See "Security".
• Add WASM support for the proxy (see [the relevant MR]).

Try it

1. Install Go.

2. Clone the code:

   git clone https://github.com/WofWca/snowflake-generalized.git \
       && cd snowflake-generalized

3. Launch the client:

   go run ./client \
       -broker-url=https://sf-dh-broker.duckdns.org/ \
       -server-url=wss://envoy1-snowflake.ce.unredacted.org:7901 \
       -listen-address=localhost:2080 \
       -destination-protocol=tcp

4. Open another terminal and access a website through the Snowflake tunnel:

   curl --proxy "socks5://localhost:2080" https://api.ipify.org

Now you can set your browser to use the SOCKS5 proxy at localhost:2080.

For more info about how this example works, see ./examples/wireguard/.

Many thanks to Unredacted.org for setting up a public SOCKS server!

Background knowledge

Snowflake is developed by The Tor Project. As of 2024, it can only be used to access the Tor network.

A Snowflake client is embedded into Tor Browser and Orbot. Orbot provides VPN-like functionality by tunneling traffic through Tor, optionally accessing Tor through bridges, such as Snowflake.

(An altered figure from the Snowflake paper (which you should check out (it's not that hard to read)))

But, as you might imagine, making your traffic bounce off of 1 + 3 relays (extra 1 is a Snowflake proxy) before it reaches the destination could be quite slow.
If you're only looking to browse Instagram or YouTube or whatever else is blocked for you, and you don't care about anonymity that Tor provides, you'd want Snowflake to connect directly (or at least more directly) to where you want to go, and not through a huge chain of relays.

Luckily, as it turns out, Tor is not inherent in Snowflake. And this is where our project comes in!

How it works

Pretty much like Snowflake. In fact you can argue that this project is just Snowflake, but with adjusted arguments.
The source code is mostly boilerplate.

Is it production-ready?

Not yet.

Not as fast as it can be (but still faster!)

Upstream Snowflake is still pending quite a lot of work to improve its performance (download speed and latency).
But at the current state of the project, 20+ Mbit / s with download latency below 700 ms is already achievable!

For reference, here are some other performance-related issues, which also include performance measurements:

• Use unreliable and unordered WebRTC data channels
• Tune reliable protocol parameters for Snowflake
• Multiplex - one client splits traffic across multiple proxies

Easy to block

The real power of a Snowflake network comes from the numerosity of its proxies. Ideally we'd want one huge Snowflake network (which the original one from The Tor Project is) where proxies are happy to pass client's traffic wherever the client wishes, without making the proxy operator install an extra browser extension or a Docker container per each server that they want to let clients get unrestricted access to.
But, as was said, by default the proxies can only forward traffic to just a few set-in-stone Tor relays.

In order to change that and let proxies connect to arbitrary addresses, we need to make a lot of hardening changes to the proxy's code such that they cannot be abused, e.g. for DDoS, access to the proxy operator's private network, or distribution of illegal content.
And I am trying to do just that with my recent MRs.

Security

So, the proxy can connect to arbitrary addresses, specified by clients. This begs the question: Is it even safe to run a proxy on a VPS, let alone from home?

To address this, we have several security layers:

• The proxy will only accept to connect to one single, somewhat obscure, port.

  We chose port 7901.

  It is not very likely (but still possible) that any services are running on this port, except a Snowflake server. So if there is no application listening on this port, the target host should simply reject such a connection, and nothing should happen.

  If the client specifies a different port, the proxy will reject such a request, and no network activity will occur at all, not even DNS (apart, of course, from sending an error response to the broker).

  See the relevant MR, "hardening(proxy): check port against relay pattern".

  (Just FYI this port is already assigned by IANA to another application, "TNOS Service Protocol". See the IANA Port Number Registry).

• The proxy will not connect to private IP addresses.

  The proxy will perform a DNS request, and verify that the target host does not resolve to any private addresses.

  If the host is at a private address, the proxy will reject the client's request, and will not send any packets to the target host.

  In addition, if the client tried to specify the target host by IP, the proxy won't even have to perform the DNS request: determining whether an IP is private requires no network activity. Note that, contrary to what one might think, private machines may and often do have a host name associated with them, for example myrouter.local (this is used e.g. by Linksys).

  The DNS check, however, is not always available in the browser extension version of the proxy. It requires the DNS permission. See dns.resolve().

  See the relevant commit, "hardening(proxy): !allowPrivateIPs: perform DNS".

• The broker will reject the client's request if the target host doesn't resolve to a public IP address.

  The broker will perform its own DNS request.

  This alone, of course, does not save the proxy if the broker goes evil, but it's still a layer of security.

  However, as was mentioned, a domain name might resolve to a public address on the broker side, but to a public address on the proxy side. For example, ASUS routers can be accessed from the home network by domain name www.asusrouter.com (see their help article on this). Even though the domain name doesn't resolve to a public address as of 2025-02, they might change their mind about it.

  See the relevant commit, "hardening(broker): DNS check if relayURL is public".

• The proxy will only accept to connect to TLS (HTTPS) servers (and not unencrypted bare HTTP servers).

  Most of the time (but not always!), HTTP servers that run on private addresses do not utilize TLS. If the target server doesn't speak TLS, the connection to it will fail. The target server will still receive packets from the proxy, but it's basically gonna looks like garbage to it.

  To the best of my knowledge, at this stage (during TLS connection establishment) the client still cannot in any way control the contents of the packets that the proxy sends to the target host.

  Note that some routers, such as Linksys (see this help article) do utilize TLS (https://192.168.1.1).

• The proxy will check if the target HTTP server is a Snowflake server.

  The proxy will send a benign HTTP GET request to the target server, with a special header (Are-You-A-Snowflake-Server). The server must respond with another header (I-Am-A-Snowflake-Server), otherwise the proxy will refuse to proceed. The contents of such a request, apart from the host address, are not controlled by the client.

  See the relevant MR, "hardening: make proxies request server consent".

• The proxy will only do WebSocket connections (later WebTransport).

  If the target server is not a WebSocket server, the connection will fail.

  This is inherent in the WebSocket protocol. See The WebSocket Protocol RFC: Opening Handshake.

• As an extra layer to ensure some of the above claims, the browser extension version of the proxy utilizes Content Security Policy (CSP). Namely, the CSP includes the following:

  connect-src
      wss://*:7901
      https://*:7901/are_you_a_snowflake_server
      https://<BROKER_DOMAIN_NAME>
      https://snowflake-broker.torproject.net:8443/probe

TODO (unimplemented) extra measures:

• Utilize WebSocket subprotocol negotiation.
• Respect the Access-Control-Allow-Origin response header.
• Make the broker perform the consent request.
• Make the broker only accept servers which registered on this broker.

Please let me know if you have ideas / concerns!

Can I run a proxy?

Yes, you can help this project help others circumvent censorship.
However, remember:

• This project is still work-in-progress. But we'll continue improving things, so I guess you could just launch the proxy and forget about it: it should update itself automatically, if you use the command below.
• It might not be safe to run a proxy on a personal machine and+or network.
  Do I think it's safe? Yes, it looks pretty safe to me. But, AFAIK, nobody else has assessed the security of my changes.

If you want to proceed:

1. Install Docker.

2. Run

   curl -O https://gitlab.torproject.org/WofWca/snowflake/-/raw/for-snowflake-generalized/docker-compose-proxy.yml \
       && docker compose -f docker-compose-proxy.yml up --detach

Again, the proxy code is based on the original Snowflake code, so you could also find Tor Project's instructions and Tor Project Forum useful.

Why did you make the project?

My dream is: Snowflake clients can access any service they want with the help of Snowflake proxies, without having to route the traffic through the (not the fastest) Tor network, and the Snowflake proxies don't have to worry about being abused, and that all VPN providers have a Snowflake server running, ready to accept clients for whom their service is blocked.

Snowflake is a fascinating concept and I think it has a lot of potential.

Usage

For a quick demo, see the "Try it" section.

Also see ./examples

---

This guide will walk you through setting up an entire Snowflake network, with all 4 of its components.
However, as a regular user, or a service provider, you'll only need to set up one: users will need to set up the client, and service providers will need to set up the server. You're supposed to be using the broker and the proxies that other people already set up publicly.

With that out of the way, let's make a setup that will work in the same way as

ssh -L localhost:2080:example.com:80 my-server-1.my-domain.com -N

That is, if you connect with TCP to localhost:2080 on your local machine, the connection will be performed to example.com:80 from my-server-1.my-domain.com.

A Snowflake network consists of components of 4 types. In production, each component usually runs on a different machine, but for testing purposes you can run all of them locally.

Prerequisites

• Install Go.

1. Set up the broker

It is not possible to use the already set up Snowflake broker maintained by The Tor Project because as of 2024 it refuses clients who ask to connect to servers other than the ones maintained by The Tor Project.
This might change in the future. Keep an eye on this issue.

1. Download the original Snowflake code.

   git clone https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake.git

2. _

   cd snowflake/broker

3. Create a list of available Snowflake servers. Replace wss://my-server-1.my-domain.com:7901 with the URL that your Snowflake server (not the broker!) is gonna listen on. We're gonna set up the said server in the next steps.

   echo '{"displayName":"my", "webSocketAddress":"wss://my-server-1.my-domain.com:7901", "fingerprint":"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"}' > bridgeListMy.txt

   This step might become unnecessary after this MR is merged.

4. Run the broker. Follow the original instructions to set up TLS ecnryption.

   Or you can run it ⚠️ without encryption. Again, replace my-server-1.my-domain.com with the hostname of your Snowflake server, and localhost:4444 with the address that you want the broker to listen on.

   go run . \
       -disable-geoip \
       -disable-tls \
       -addr=localhost:4444 \
       -allowed-relay-pattern='^my-server-1.my-domain.com$' \
       -bridge-list-path=bridgeListMy.txt

2. Set up a proxy

1. Download the original Snowflake code.

   git clone https://gitlab.torproject.org/tpo/anti-censorship/pluggable-transports/snowflake.git

2. _

   cd snowflake/proxy

3. Run the proxy.

   Replace http://localhost:4444 with the URL of your broker, and ^my-server-1.my-domain.com$ with the same pattern that you set for the broker (i.e. your server's hostname).
   Omit keep-local-addresses in production.

   go run . \
       -broker='http://localhost:4444' \
       -verbose \
       -allowed-relay-hostname-pattern='^my-server-1.my-domain.com$' \
       -allow-non-tls-relay \
       -keep-local-addresses

3. Set up the server

1. Download this project's code.

   git clone https://github.com/WofWca/snowflake-generalized.git

2. _

   cd snowflake-generalized/server

3. Run the server.

   Replace example.com:80 with the desired destination. In practice you'd want it to be a SOCKS / VPN / Tor server running on the same machine as the server. Also replace localhost:7901 with :7901 if you want the server to be publicly reachable. ⚠️ Remove -disable-tls and add acme-hostnames=... to enable encryption.

   go run . \
       -destination-address='example.com:80' \
       -listen-address='localhost:7901' \
       -disable-tls

4. Run the client

1. Download this project's code.

   https://github.com/WofWca/snowflake-generalized.git

2. _

   cd snowflake-generalized/client

3. Run the client!

   Again, replace broker-url with the URL of the broker from a previous step and (optionally) server-id with the one that you used in bridgeListMy.txt.
   Omit keep-local-addresses in production.

   go run . \
       -listen-address='localhost:2080' \
       -broker-url='http://localhost:4444' \
       -server-id='AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA' \
       -keep-local-addresses

Now open up the browser and go to http://localhost:2080. If you see a dummy 404 page, then it worked!

Now feel free to replace example.com:80 with a real service of your choosing.

Similar projects

• Snowflake. Well, this project is based on Snowflake.
• Snowstorm. A WIP project by the original Snowflake author. Seems very similar to this project in spirit. Claims to be optimized for high speed and low latency.
• Lantern's Unbounded (source code). Also very similar. Development started after Snowflake has been released, so it hopefully avoids unfortunate design decisions of Snowflake, for example it's already using WebTransport, as opposed to WebSocket used by Snowflake. WebTransport should be faster.
• Ceno Browser. Similar because peer-to-peer, but seems to be webpage-oriented, i.e. it fetches cached versions from peers using BitTorrent. But there is a lot more to it, so better check their manual.
• MassBrowser. The difference is that proxies act as exit nodes and not just middle nodes like in Snowflake and in this project, so it's not as safe to run a proxy. And the project seems a bit abandoned as of 2025-01.
• SpotProxy. Doesn't seem super similar, but there is a similarity in the fact that proxies are ephemeral, and there is explicit support for switching between them.

Please let me know if you know other similar projects!

Addendum

Thanks to The Tor Project for making the Snowflake library easy to use!