Hi Haxxpop,

> On 15 Aug 2019, at 16:53, Pop Chunhapanya <p...@cloudflare.com> 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.

T
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