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Re: [openpgp] Fingerprint requirements for OpenPGP

Derek Atkins <derek@ihtfp.com> Wed, 13 April 2016 14:20 UTC

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From: Derek Atkins <derek@ihtfp.com>
To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
References: <87vb3nslqh.fsf@alice.fifthhorseman.net> <20160412083409.GA16775@littlepip.fritz.box> <87egaarj74.fsf@alice.fifthhorseman.net>
Date: Wed, 13 Apr 2016 10:20:36 -0400
In-Reply-To: <87egaarj74.fsf@alice.fifthhorseman.net> (Daniel Kahn Gillmor's message of "Tue, 12 Apr 2016 10:32:47 -0400")
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Cc: IETF OpenPGP <openpgp@ietf.org>, Vincent Breitmoser <look@my.amazin.horse>
Subject: Re: [openpgp] Fingerprint requirements for OpenPGP
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Daniel Kahn Gillmor <dkg@fifthhorseman.net> writes:

> On Tue 2016-04-12 04:34:09 -0400, Vincent Breitmoser wrote:
>>Daniel Kahn Gillmor(dkg@fifthhorseman.net)@Mon, Apr 11, 2016 at
>> 08:40:22PM -0400:
>>> * it should be cheap to compute from a given key -- you shouldn't need
>>>   a gig of RAM or a minute of CPU to calculate the fingerprints of any
>>>   key.
>>
>> Strictly speaking, we can be slightly less restrictive: It must be
>> cheap to verify, given a fingerprint, that it's the correct one for a
>> key.  This distinction does not make a difference unless we store the
>> fingerprints as part of the data format (which we probably shouldn't),
>> so this is more of an academic point.
>
> Right, i don't think we should store the fingerprint as part of the data
> format, so we still need to be able to rapidly generate it, not just
> verify it.

Nothing stops an implementation from storing the computed fingerprint
alongside the key/certificate.  Indeed, I would encourage
implementations to do just that for speed, especially with extremely
large keyrings.

-derek
-- 
       Derek Atkins                 617-623-3745
       derek@ihtfp.com             www.ihtfp.com
       Computer and Internet Security Consultant

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