On 07/19/2016 02:42 AM, grarpamp wrote: > https://cryptome.org/2016/07/cloudflare-de-anons-tor.htm > > 18 July 2016 > > Cloudflare reCAPTCHA De-anonymizes Tor Users > > A sends: > > Cloudflare's insistence on solving reCAPTCHA puzzles when visitors are > coming from Tor exit nodes to one of the 2 million web sites that > Cloudflare 'protects' can be very instrumental for traffic analysis > and de-anonymizing of Tor users. > > This is how: > > The only non-public prerequisite for the de-anonymizing entity is the > ability to monitor traffic between ISPs and Tor entry nodes, and > traffic entering Cloudflare servers (no decryption required in either > case). There are, of course, no 2 million Cloudflare servers, probably > there is no more than few hundred. > > Each click on one of the images in the puzzle generates a total of > about 50 packets between Tor user's computer and the Cloudflare's > server (about half are requests and half are real-time responses from > the server.) All this happens in less than a second, so eventual > jitter introduced in onion mixing is immaterial. The packet group has > predictable sizes and patterns, so all the adversary has to do is note > the easily detectable signature of the "image click" event, and > correlate it with the same on the Cloudflare side. Again, no > decryption required. > > There likely are many simultaneous users (thousands), but they do not > solve puzzles at the same time, and they do not click on the puzzle > image at the same time. Simple math shows that disambiguating is > trivial. If there is some ambiguity left, Cloudflare can conveniently > serve few more images to specific users (or even random users, as long > as within the same few seconds different users get different amount of > 'correct' images.) > > This obvious opportunity is not the proof, but NSA would have to be > utterly incompetent not to be exploiting it. No one is that > incompetent. >
I pointed out this possibility regarding Hushmail in February 2015. http://auntieimperial.tumblr.com/post/111007562804 http://66.media.tumblr.com/acc793091fadb7eabc16dbf9705b2be3/tumblr_njs0wgovEO1r9ju7do2_1280.png It's especially treacherous if you do have something to hide, and helps them tune their shit, if you log in on tor, and also barefoot, at different times.
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