Re: [secdir] [Dots] Secdir telechat review of draft-ietf-dots-signal-channel-31

Stephen Farrell <stephen.farrell@cs.tcd.ie> Mon, 15 April 2019 14:57 UTC

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To: "Konda, Tirumaleswar Reddy" <TirumaleswarReddy_Konda@McAfee.com>, "mohamed.boucadair@orange.com" <mohamed.boucadair@orange.com>, "secdir@ietf.org" <secdir@ietf.org>
Cc: "draft-ietf-dots-signal-channel.all@ietf.org" <draft-ietf-dots-signal-channel.all@ietf.org>, "ietf@ietf.org" <ietf@ietf.org>, "dots@ietf.org" <dots@ietf.org>
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From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Date: Mon, 15 Apr 2019 15:57:49 +0100
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Subject: Re: [secdir] [Dots] Secdir telechat review of draft-ietf-dots-signal-channel-31
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On 15/04/2019 15:38, Konda, Tirumaleswar Reddy wrote:
>> -----Original Message----- From: Dots <dots-bounces@ietf.org>; On
>> Behalf Of Stephen Farrell Sent: Monday, April 15, 2019 6:56 PM To:
>> mohamed.boucadair@orange.com; secdir@ietf.org Cc:
>> draft-ietf-dots-signal-channel.all@ietf.org; ietf@ietf.org;
>> dots@ietf.org Subject: Re: [Dots] Secdir telechat review of
>> draft-ietf-dots-signal-channel-31
>> 
>> 
>> Hiya,
>> 
>> On 15/04/2019 14:16, mohamed.boucadair@orange.com wrote:
>>>> - p13: The cuid still seems to me to be too static (there's a
>>> 
>>> [Med] This is a feature not a bug. This scheme is particularly
>>> useful to recover state, for example, upon reboot or crash of a
>>> DOTS client.
>>> 
>> 
>> Well, fair enough, but FWIW I'm not convinced that a client that
>> can keep state (the private key and other dots stuff) couldn't also
>> as easily keep a cuid value. And ISTM there should also be equally
>> good ways to recommend for generating a cuid that don't have that 
>> 1:1 mapping to a key pair. All that said, it's not me needs to be
>> convinced, but the IESG, so probably best to wait and see if they
>> think this is worth changing or not before doing so.
> 
> The advantage of the 1:1 mapping is the DOTS servers can validate the
> DOTS client is not using the 'cuid' of another client.

So that'd be "an" advantage, if it is one;-)

But given the servers are supposed to authenticate
the client via TLS client-auth (or else the server
doesn't see the public key), I don't see the need.
Nor do I recall that the server is supposed to compare
the key to the cuid - if that check is to be done,
then that'd need to be in the spec or a client that
re-keys would have to make a new cuid. (Apologies
if that's in the spec and I've forgotten it.)

Cheers,
S.


> 
> -Tiru
> 
>> 
>> S.
>> 
>