Couldn't connect to server through obfsproxy( & where to get the latest document)?

Question

I'm recently running openvpn in openwrt-x86-generic, and I want to use obfsproxy to obfuscate the traffic.

The problem is that the package of obfsproxy in openwrt(which I use as a openvpn server) has been abandoned for quite a long time, so the latest version I can get through opkg is 0.1.4. However, in a PC running windows xp(which is a client), the oldest version of obfsproxy I can get through pip install is 0.2.1. When I try to connect the server, it always cast an error saying corrupted magic number, which is likely to be the version problem.

I've tried from 0.2.1 to 0.2.13 in client, none of which worked. There seems to be no specific document on this problem, and it seems complicated now since the package in openwrt in nolonger maintained.

Could anyone give me some advice on how to solve it, or offer some reference about obfsproxy?

BTW, I'm using obfs2 method, but I don't think that is the key problem.

Thanks. Tgn

Answer 1

obfs2 should be considered dead and buried. A passive observer can remove the obfuscation (and an active attacker can remove obfs3).

The "Corrupted magic value" is actually part of the protocol, it's not related to the "version number", it expects that a "magic" value (obfs2.py, obfs2.h) is part of the decrypted message.

You can read more about obfs2 here, it includes example code that should allow you to reconstruct and review the key exchange from a packet capture.

They should be interoperable, using 0.2.13 obfs2.py as the client and 0.1.4 obfsproxy as the server:

setup the server:

$ ./obfsproxy obfs2 --dest=127.0.0.1:31337 server 127.0.0.1:31338
2016-xx-xx xx:xx:xx [notice] Starting (obfsproxy version: 0.1.4 (git-94ebc4c3edf1e3e5)).

setup the client:

$ ./bin/obfsproxy obfs2 --dest 127.0.0.1:31338 client 127.0.0.1:31339
2016-xx-xx xx:xx:xx,xxx [WARNING] Obfsproxy (version: obfsproxy-0.2.13-1-g2bf9d09) starting up.
2016-xx-xx xx:xx:xx,xxx [WARNING] Pyptlib version: 0.0.6

connect into the client and send some data:

$ ncat 127.0.0.1 31339 -c 'echo "Hello, this is dog."'

and the receiving end-point receives it over obfs2:

$ ncat -l 127.0.0.1 31337
Hello, this is dog.

So "Hello, this is dog." was sent into the waiting 0.2.13 obfs2.py client listener, across to the 0.1.4 obfsproxy server listener and out to the destination.

You should, however, stop using obfs2 and upgrade to obfs4. For how to cross-compile it, try this answer and incorporate setting environment variables in the launch script, in line with pt-spec.txt.