Re: Structuring the BKK spin bit discussion

Martin Thomson <martin.thomson@gmail.com> Mon, 29 October 2018 22:30 UTC

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References: <18A2F994-0E82-48E4-875D-93C674483D49@eggert.org> <20181029160802.GD7258@ubuntu-dmitri> <8268B90E-F109-424C-91A8-DB7BFE208F53@huitema.net>
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From: Martin Thomson <martin.thomson@gmail.com>
Date: Tue, 30 Oct 2018 09:29:53 +1100
Message-ID: <CABkgnnU7W-_o_EGZWpJvTGRSm0KiL-hS7q_oQ6kT3LBoNKHGhw@mail.gmail.com>
Subject: Re: Structuring the BKK spin bit discussion
To: Christian Huitema <huitema@huitema.net>
Cc: Dmitri Tikhonov <dtikhonov@litespeedtech.com>, Lars Eggert <lars@eggert.org>, QUIC WG <quic@ietf.org>
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On Tue, Oct 30, 2018 at 3:54 AM Christian Huitema <huitema@huitema.net>; wrote:
> I think the strongest objection to the spin bit was put up by Marten during the last interim: measuring the RTT with the spin bit discloses the use of hidden path segments like VPN. This issue was not discussed during the privacy analysis.

I had assumed that was part of the analysis and it was covered by the
assumption that spinning could be disabled

> One solution would be to remove the spin bit from the spec, trading off better privacy for worse management. I am considering another solution in which privacy sensitive clients hide the RTT by controlling the spin, for example spinning at fixed intervals. I plan testing that option in Picoquic.

I've done a little thinking about this one, and it might conflict with
the natural signals the transport emits, along the lines of what
Andrew McGregor has mentioned on a couple of occasions.  If the spin
bit is enabled, then privacy-sensitive endpoints will need to make a
hard call regarding standing out.

Note also that you probably can't hide the fact that you aren't at the
same network location as the address you are using.  Spoofing a
shorter RTT is impossible in general because you have to assume edges
that haven't arrived yet.  If there are no edges you expose the
charade.