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Re: [tor-talk] Using public Wi-Fi for access

Thus spake David Carlson (carlson.dl@xxxxxxxxxxxxx):

> I would like some advice about accessing Tor through public wi-fi
> networks at airports, hotels, Starbucks and Mc Donalds.  I did not
> find information about this that ordinary people could understand on
> the torproject faq page.
> I would suppose that, in general, they keep logs which probably
> include MAC addresses and access times, durations and whatever. 
> This could be used by either police or criminals to track use of my
> computer around the globe.  Also, some of these networks use the
> technique of blocking all access until an attempt is made to use
> http, whereupon they hijack the attempt to redirect to their log-in
> page.  Then, if the log-in is successful, they finally allow
> whatever traffic they consider acceptable from, I suspect, that
> particular MAC address.
> Is this conjecture all wet, or am I correct that I am probably
> compromised if I use public wi-fi?

You are entirely correct in your guess as to how the system works,
authenticates you, and tracks you.

However, this does not mean that you're "compromised". If you use a
default Tor, the wifi owner will at best see you log in, and then see
that you are Tor user, and not much after that. If you are using Tor
with bridges, they will likely not know even this much.

> Is there a way to use public wi-fi safely?

If you are on a Linux system, you can get the package 'macchanger',
which can spoof your mac address to valid addresses by arbitrary
vendors.  This can alleviate the risk of your laptop being tracked
from access point to access point. Similar utilities exist for
Windows. For MacOS, Steve Jobs deemed that you must be tracked at all
times (he likes to 'Think Different'), unless you decide to purchase a
USB wifi device, in which case he will allow you to change the MAC
address from the command line using 'ifconfig'.

However, a serious adversary may still be able to fingerprint your
wireless driver based on the 802.11 protocol headers[1], or if there
is a big white van parked nearby, by the actual radio signature of
your specific device[2]. The former will not specifically deanonymize
your device, but likely just narrow it down to chipset and possibly
driver version. The exact capabilities of latter in the field are not
widely known. Ambient noise and other devices may likely interfere
with RF fingerprinting on a large scale. 

1. http://www.sandia.gov/news/resources/releases/2006/images/wireless-fingerprinting.pdf
2. http://petsymposium.org/2008/hotpets/mccoyd_hotpets2008.pdf

Mike Perry
Mad Computer Scientist
fscked.org evil labs

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