Re: [tor-dev] Putting onion services behind a third-party TCP proxy

Hi Haxxpop,

On 15 Aug 2019, at 16:53, Pop Chunhapanya <pop@xxxxxxxxxxxxxx> wrote:

So I'm thinking putting the tor daemon behind some third party TCP proxy that will protect me from this kind of DDoS attack.

What do you think if I want to implement a feature that forward all the onion service traffic to the TCP proxy before going to the Tor network?

The protocol that I'm thinking is TCP Proxy Protocol [1]

[1] https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt

You could try the existing HTTPSProxy torrc option?

HTTPSProxy host[:port]
Tor will make all its OR (SSL) connections through this host:port (or host:443 if port is not specified), via HTTP CONNECT rather than connecting directly to servers. You may want to set FascistFirewall to restrict the set of ports you might try to connect to, if your HTTPS proxy only allows connecting to certain ports.

Tor also allows an intelligent firewall to filter circuits using a field in haproxy protocol format, see HiddenServiceExportCircuitID for details. But you probably won't need this advanced feature.

I feel that HTTPSProxy is too expensive. As far as I know, it needs to do (1) tcp handshake, (2) tls handshake, and (3) http connect. If I can use haproxy, it would be just one tcp handshake.

Could I propose another option for haproxy?
I can do it myself. You just review and merge :)

Sure, I suggest you use this torrc option format:

TCPProxy protocol host:port

Tor will use the given protocol to make all its OR (SSL) connections through a TCP proxy on host:port, rather than connecting directly to servers. You may want to set FascistFirewall to restrict the set of ports you might try to connect to, if your proxy only allows connecting to certain ports. There is no equivalent option for directory connections, because all Tor client versions that support this option download directory documents via OR connections.

The only protocol supported right now 'haproxy'. This option is only for clients. (Default: none)

The haproxy protocol works in the following way: when the feature is enabled, the Tor process will write a header line on every outbound connection. The header is in the following format:

"PROXY" [ "TCP4" | "TCP6" ] SourceIPAddress DestinationIPAddress SourcePort DestinationPort "\r\n"

There is a single space after each item, except for the last item, which is followed by a CRLF.

After parsing a correctly-formatted PROXY line, the haproxy connects to DestinationIPAddress:DestinationPort, and forwards all subsequent data to the destination. Any data sent by the destination is forwarded by haproxy to the Tor client.

The HAProxy version 1 proxy protocol is described in detail at https://www.haproxy.org/download/1.8/doc/proxy-protocol.txt

I don't think you'll need to implement a TCPProxyAuthenticator option.