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Re: [Full-disclosure] Firefox 2.0.x: tracking unsuspecting users using TLS client certificates

It occurs to me that this could be used to good effect to track someone using Tor across various domains you control. Most Tor users know to kill JS, Flash, and are more than normally paranoid about cookies, but may not think twice about accepting a client certificate. I'm CC'ing the Tor mailing list to see what they think...

Can anyone see if this works through Privoxy and the other things in the standard Tor bundle?


On 9/7/07, Eddy Nigg (StartCom Ltd.) <eddy_nigg@xxxxxxxxxxxx> wrote:
Hi Alexander,

Alexander Klink wrote:
Granted, if this is a "real" CA. But if you use it like in my PoC not
for the typical CA scenario, but for user tracking, you could put all
kinds of data in the certificate.
That's right. Still I believe that the generation of a private key and issuance of the certificate is pretty "noisy". However I agree, some explanation would be better. Obviously on a CA, this process is explained at the web site, but as in your scenario, the user isn't supposed to know a lot about it....There is something to your claim....
Tracking visitors in an unnoticed way over several domains is typically
not as easy as this, I believe.
Well ,well... ;-)
I've actually tested that again and it also works in Firefox 1.5 - and
even "better" there, because the certificate installation does not show
any dialog at all.
Right! In 1.5 no "Installation Message" appears, which in 2.0 has been corrected. I suggest to file a bug with the request to change the default settings for handling certificate authentication. Please send the bug number, so we can vote for it...

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