Re: [DNSOP] Secdir last call review of draft-ietf-dnsop-server-cookies-04

Willem Toorop <willem@nlnetlabs.nl> Wed, 02 December 2020 21:39 UTC

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To: Stephen Farrell <stephen.farrell@cs.tcd.ie>, Ondřej Sur ý <ondrej@isc.org>
Cc: last-call@ietf.org, draft-ietf-dnsop-server-cookies.all@ietf.org, dnsop@ietf.org, secdir@ietf.org
References: <160693121881.9413.5642470305677631145@ietfa.amsl.com> <17AFD6F5-11DA-41BC-8C37-E1893648041D@isc.org> <75c266ba-573a-29e3-621d-aea9b27f195f@cs.tcd.ie>
From: Willem Toorop <willem@nlnetlabs.nl>
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Date: Wed, 02 Dec 2020 22:38:22 +0100
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Subject: Re: [DNSOP] Secdir last call review of draft-ietf-dnsop-server-cookies-04
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Op 02-12-2020 om 21:37 schreef Stephen Farrell:

<snip>

>> ad 2) we need a value that’s synchronized well enough and monotonic.
>> I honestly don’t see any value in using 64-bit value here. Using
>> unixtime has a value in itself, it’s a well-known and there’s a
>> little room for any implementer to make a mistake in an
>> implementation. The interoperability is more important than the
>> actual value of the counter. It’s write only counter, nobody is going
>> to interpret it after it has been generated, and it’s wide enough to
>> prevent brute forcing.
> 
> So what happens after 2038? That's really not v. far in the
> future any more.

The draft states that `All comparisons involving these fields MUST
use "Serial number arithmetic", as defined in [RFC1982]'. So it can not
be used to compare differences larger than 68 years, but comparisons of
cookie timestamps are more in the "hours" order of magnitude.

Cheers,
-- Willem

> 
> Cheers,
> S.
> 
>>
>> Cheers, Ondřej -- Ondřej Surý — ISC (He/Him)
>>
>>> On 2. 12. 2020, at 18:47, Stephen Farrell via Datatracker
>>> <noreply@ietf.org> wrote:
>>>
>>> Reviewer: Stephen Farrell Review result: Has Issues
>>>
>>> I see two issues here worth checking:
>>>
>>> 1. I don't recall SipHash being used as a MAC in any IETF standard
>>> before. We normally use HMAC, even if truncated. Why make this
>>> change and was that checked with e.g. CFRG? (And the URL given in
>>> the reference gets me a 404.)
>>>
>>> 2. Is it really a good idea to use a 32 bit seconds since
>>> 1970-01-01 in 2020? I'd have thought that e.g. a timestamp in hours
>>> since then or seconds since some date in 2020 would be better.
>>>
>>> Here's a couple of nits too: - section 1: what's a "strong
>>> cookie"? - "gallimaufry" - cute! but not sure it'll help readers to
>>> learn that word.
>>>
>>>
>>>
>>>
>>
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> 
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