❄️ 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 majority of the changes relevant to this project are in that fork. 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

Install Go.

Clone the code:

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

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

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:

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.
- Standalone (native) proxy:
  
  The standalone (native) 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.
  
  See the relevant commit, "hardening(proxy): !allowPrivateIPs: perform DNS".
- Browser-based proxy:
  
  The DNS check, however, is not always available in the browser extension version of the proxy. It requires the DNS permission, which Chromium does not support, as of 2025-03. See dns.resolve().
  
  In browsers we will rely on the concept called "Private Network Access" (PNA). When the browser determines that the target server is located on a private address (such as 127.0.0.1 or 192.168.1.1), it will perform a preflight request to the server, and expect it to explicitly specify in the response headers that it allows public origins to access it (Access-Control-Allow-Private-Network: true). If this is not the case, the proxy will refuse to proceed. "Private Network Access" is not yet fully adopted by browsers, but we are prepared for it: we set the treat-as-public-address CSP directive.
  
  Note that, at the current state, PNA is more invasive, because it does perform an HTTP request to the target server, unlike a simple DNS request.
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 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 OPTIONS 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. This is similar to the existing concept called "preflight requests".

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.
The proxy will check if the WebSocket server claims to support the Snowflake-specific subprotocol.

In some cases the WebSocket connection will fail at hanshake level (e.g. in Chromium). If that didn't happen, we'll explicitly verify that the WebSocket server picked the right protocol name string.

See the relevant commit, "hardening: RequireWebSocketSubprotocolNegotiation".
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
```
Side-channel attack protection.

For the majority of the abovementioned checks, if a check fails, the proxy will not reveal any information to the client about the kind of error that occured. This includes timing attack protection: the proxy will respond to the client after a fixed amount of time, should an error occur.

TODO (unimplemented) extra measures:

Improve / ensure resiliance against DNS rebinding attacks (CAPEC-275: DNS Rebinding) In the context of our project, this applies to the "consent" OPTIONS request, which is performed prior to the actual WebSocket connection, i.e. the consent request and the WebSocket connection might actually go to different addresses. This is a form of a "time-of-check to time-of-use" (TOCTOU) vulnerability (CWE-367).

As of 2025-03, this is attack is mitigated by the use of TLS, WebSocket subprotocol negotiation, and destination port limiting (:7901) (see above).
Make the broker perform the consent request.
Make the broker only accept servers which registered on this broker.

In general, the class of vulnerabilities that the proxy is most open to is CWE-918: Server-Side Request Forgery (SSRF).

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:

Install Docker.

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.

Download the original Snowflake code.

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

_
```
cd snowflake/broker
```
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.
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

Download the original Snowflake code.

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

_
```
cd snowflake/proxy
```
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

Download this project's code.

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

_
```
cd snowflake-generalized/server
```
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

Download this project's code.

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

_
```
cd snowflake-generalized/client
```
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!

Name		Name	Last commit message	Last commit date
Latest commit History 49 Commits
client		client
common		common
docs		docs
examples		examples
server		server
README.md		README.md
go.mod		go.mod
go.sum		go.sum

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❄️ Snowflake Generalized

Try it

Background knowledge

How it works

Is it production-ready?

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

Easy to block

Security

Can I run a proxy?

Why did you make the project?

Usage

Prerequisites

1. Set up the broker

2. Set up a proxy

3. Set up the server

4. Run the client

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❄️ Snowflake Generalized

Try it

Background knowledge

How it works

Is it production-ready?

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

Easy to block

Security

Can I run a proxy?

Why did you make the project?

Usage

Prerequisites

1. Set up the broker

2. Set up a proxy

3. Set up the server

4. Run the client

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