Re: [openpgp] New fingerprint: to v5 or not to v5

Jonathan McDowell <noodles@earth.li> Sat, 10 October 2015 10:35 UTC

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Date: Sat, 10 Oct 2015 11:35:49 +0100
From: Jonathan McDowell <noodles@earth.li>
To: openpgp@ietf.org
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References: <878u84zy4r.fsf@vigenere.g10code.de> <87fv1xxe5w.fsf@alice.fifthhorseman.net> <87r3lgcup8.fsf@vigenere.g10code.de> <CACsn0c=-LKagSqTbgOV1W4Gu4u-f6vpVq82-nWSLGogjoeFKeg@mail.gmail.com> <CAMm+LwjeKDKnN2ZAisbKhWVS4kwCEm_VvcZ1MtftYzEJQpGdhg@mail.gmail.com> <87y4fi5wa9.fsf@vigenere.g10code.de> <9A043F3CF02CD34C8E74AC1594475C73F4B278ED@uxcn10-5.UoA.auckland.ac.nz> <8737xp5z45.fsf@vigenere.g10code.de> <56128637.6030504@iang.org> <87wpuvx4o1.fsf@alice.fifthhorseman.net>
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Subject: Re: [openpgp] New fingerprint: to v5 or not to v5
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On Fri, Oct 09, 2015 at 02:44:46PM -0400, Daniel Kahn Gillmor wrote:
>  a) don't include any key creation time at all; signatures themselves
>     have a creation time, which is sufficient.
> 
>  b) include key creation time in the material certified only for
>     self-sigs (certifications issued by the key itself).  Do not include
>     any key creation time in the material certified by third-parties.
> 
>  c) Include creation time of the certified key in the material certified
>     for all certifications -- first-party or third-party.
> 
> I'm tempted by the simplicity of (a), to be honest.
> 
> (b) sounds doable, but i don't know how useful it is to have assertions
> from the key of when the key was created, or what to do with situations
> where some self-sigs assert a different key creation time than others.
> Should we reject or ignore some of them?  if so, which ones?
> 
> (c) sounds like trouble -- you'll get self-signed assertions of key
> creation time that don't match third-party assertions of key creation
> time.  What does that mean?  how should it be represented to the user?
> I think this is the issue that Werner was hinting at.
> 
> what are the downsides of (a)?  What are the advantages of having a key
> creation time at all?  Is it simply that it provides a universally-known
> temporal boundary when to accept signatures made by that key?

I've certainly used key creation time as a separate piece of information
to "most recent self-signature". The latter indicates how recently the
key can be seen as still in use / maintained, but the former gives an
idea of how long it's been around and can help when making a decision
about which of multiple keys to use for an individual. I think having
that in the self-sig would work ok (i.e. option b). In general is the
most recent self-sig not the one that should be trusted, with perhaps a
warning if any of the previous ones have a different creation time
listed?

J.

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