Re: [tcpm] Privacy problems of TCP Fast Open
Michael Tuexen <michael.tuexen@lurchi.franken.de> Tue, 21 May 2019 16:34 UTC
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From: Michael Tuexen <michael.tuexen@lurchi.franken.de>
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Date: Tue, 21 May 2019 18:34:38 +0200
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To: sy@informatik.uni-hamburg.de
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Subject: Re: [tcpm] Privacy problems of TCP Fast Open
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> On 21. May 2019, at 14:25, Erik Sy <sy@informatik.uni-hamburg.de> wrote: > > > On 5/21/19 12:18, Michael Tuexen wrote: >>> On 21. May 2019, at 09:52, Erik Sy <sy@informatik.uni-hamburg.de> wrote: >>> >>> Hi Michael, >>> >>> thanks for this question! >>> >>> Yes, TFO cookies are bound to the clients (local) IP address. However, a >>> client with a static local IP address in a home network will use the >>> same TFO cookie independently of it's publicly visible IP address. As a >>> result, TFO cookies present an independent tracking mechanism, which >>> does not necessarily rely on the client's publicly visible IP address. >> How often do the public addresses change? > > I do not have a general answer to your question. In the case of my home > network, my ISP assigns me at least every 24 hours a new IPv4 address. I also had this on my DSL line (I guess we both live in Germany), but since my telephone line was moved to "all IP", the assignment stays up for months. > Additionally, I can initiate a change of my network's public IP address > at anytime. Sure. > > TFO cookies allow basically unlimited tracking periods because they do > not have an expiration mechanism. Thus, even infrequently changed IP > addresses can be correlated. An implementation can do implement such a thing and even allow an API for it. For testing I'm flushing the cookie cache quite often... > >> One could extend the TFO API in >> a way that the application can request a new cookie by only sending >> a cookie request. > > I do not think this is an appropriate countermeasure. > > From my perspective, caching TFO cookies in the kernel is a more > fundamental privacy problem. This design requires applications to share > a pool of TFO cookies, which allows tracking across several > applications. For example, this prevents user's to separate their online > activities across different browsers. They would share the IP address. If they decide to trigger a new address binding on the access router, why couldn't they trigger flushing the cache? Best regards Michael > >>> Returning to your example, onion routing does not necessarily protect >>> you against tracking via TFO cookies. >> Yepp, that is what I wanted to say. >> But using TFO in that case doesn't >> make much sense. > > Yes, TFO does not make sense if user privacy is at stake. Thus, we > should warn users about these risks of RFC 7413. > > Best regards, > Erik > >
- [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Tuexen
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Welzl
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Tuexen
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Brian Trammell (IETF)
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Tuexen
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Tuexen
- Re: [tcpm] Privacy problems of TCP Fast Open Praveen Balasubramanian
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Tuexen
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Welzl
- Re: [tcpm] Privacy problems of TCP Fast Open Olivier Bonaventure
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Praveen Balasubramanian
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Tuexen
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Tuexen
- Re: [tcpm] Privacy problems of TCP Fast Open Erik Sy
- Re: [tcpm] Privacy problems of TCP Fast Open Michael Tuexen