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

Stephen Farrell <stephen.farrell@cs.tcd.ie> Wed, 02 December 2020 21:49 UTC

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To: Willem Toorop <willem@nlnetlabs.nl>, Ondřej Surý <ondrej@isc.org>
Cc: last-call@ietf.org, draft-ietf-dnsop-server-cookies.all@ietf.org, dnsop@ietf.org, secdir@ietf.org
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From: Stephen Farrell <stephen.farrell@cs.tcd.ie>
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Date: Wed, 02 Dec 2020 21:49:15 +0000
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Subject: Re: [DNSOP] Secdir last call review of draft-ietf-dnsop-server-cookies-04
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Hiya,

On 02/12/2020 21:38, Willem Toorop wrote:
> 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.

Sorry for being dim, but is clear what value to put
in those 4 octets in say 2039 such that different
implementations will do the right thing? I did glance
at rfc1982, so there may be very far-sighted text
in there that I missed:-) And it may even be fine
for this purpose if different servers differ by a
second or so at that point, but even if so, it may
be a bad plan to leave that unspecified in case
other timestamps use the same code.

Cheers,
S.

> 
> 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.
>>>>
>>>>
>>>>
>>>>
>>>
>>> _______________________________________________ DNSOP mailing list
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>>>
>>
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> 
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