Re: [dbound] draft-brotman-rdbd

Stephen Farrell <stephen.farrell@cs.tcd.ie> Mon, 01 April 2019 17:17 UTC

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To: John Levine <johnl@taugh.com>, dbound@ietf.org
References: <20190401161900.764062011356DA@ary.qy>
From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Date: Mon, 1 Apr 2019 18:17:07 +0100
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Subject: Re: [dbound] draft-brotman-rdbd
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Hiya,

On 01/04/2019 17:18, John Levine wrote:
> In article <cb41ecd0-c48d-b204-7ab1-f59ff330bda3@cs.tcd.ie>; you write:
>> Fully agree that cache poisoning is a relevant threat for any
>> application that would use RDBD values read from DNS without
>> sufficient additional local validation to make a decision.
> 
> Could you give some concrete examples of additional local validation,
> other than DNSSEC?

Sure. In my use-case (surveys), I keep the keys used from one
scan to the next, so e.g. I have about 4 scans of Irish and
other SMTP servers taken over the last 18 months and can see
when some keys do or don't change. Were RDBD deployed, I'd do
the same for those keys, if they got used. (To be clear, I've
not been doing that for DKIM keys to date, but for TLS and SSH
server keys.)

> As far as I can tell nobody does anything like that for DKIM keys.

I don't know if anyone does, but wouldn't be surprised if
some anti-abuse folks reacted to a mail provider switching
from one long-lived key selector to a new one not seen
anywhere before. (But I'm speculating there, others who do
that kind of thing for real would need to confirm that or
not.)

Cheers,
S.


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