Re: Pseudorandom Flow Labels

Brian E Carpenter <brian.e.carpenter@gmail.com> Thu, 07 April 2011 07:31 UTC

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Message-ID: <4D9D6898.4090502@gmail.com>
Date: Thu, 07 Apr 2011 19:32:40 +1200
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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To: Fernando Gont <fernando@gont.com.ar>
Subject: Re: Pseudorandom Flow Labels
References: <BD901061-96AC-4915-B7CE-2BC1F70861A5@castlepoint.net> <201104052036.p35KaoHV019253@cichlid.raleigh.ibm.com> <4D9CAF52.9050805@gont.com.ar> <87F2B923-3FC6-4879-8C81-B9C283AC5EA0@castlepoint.net> <4D9CE62C.4070804@gont.com.ar>
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Cc: Thomas Narten <narten@us.ibm.com>, 6man List <ipv6@ietf.org>
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Setting the flow label by calling random() cannot be a stateless
method - it would mean storing the value for use on future packets
of the same flow. We need a stateless method.

    Brian

On 2011-04-07 10:16, Fernando Gont wrote:
> Hi, Shane,
> 
> On 06/04/2011 06:44 p.m., Shane Amante wrote:
> 
>>> * We want Flow Labels that unpredictable by off-path attackers
>>> (history has taught us that this is a good proactive measure) * We
>>> want an algorithm for generating FL that produces FLs that do not 
>>> repeat with a high frequency (i.e., they are distributed normally)
>> I like your (attempt at) a more precise definition that Thomas has
>> been asking for.
>>
>> I would think another desirable property of (host-generated?)
>> flow-labels might be that, by default, they strive to preserve
>> privacy of the transmitter.  IOW, flow-labels cannot be used to track
>> individuals (over time), because they are traceable back to a
>> particular implementation or, worse, a specific device.
> 
> While I agree with this, this seems to be like a requirement for
> psedu-randomness.
> 
> That is, if all hosts in my local network set the FL with random(), and
> only my hosts implements the hash based scheme in e.g.
> draft-gont-flowlabel-security, then you might argue that the FL could be
> exploited to track me (or well, actually identify my host in my local
> network, even if I'm using privacy addresses).
> 
> But this is already the case for virtually all protocol parameters on
> which there's some room for choice. (From TCP's initial window to IPv6
> Hop Limit value, etc.)
> 
> Thanks,