[openpgp] Re: Review of draft-ietf-openpgp-replacementkey-04

Hi Andrew,

Am 12.08.25 um 09:18 schrieb Andrew Gallagher:
> Hi, Falko.
>
> On 12 Aug 2025, at 07:04, Falko Strenzke <[email protected]> wrote:
>>
>> Am 08.08.25 um 01:30 schrieb Andrew Gallagher:
>>>
>>> I think we can describe Key Equivalence Groups without referring 
>>> specifically to User ID packets, but rather to the underlying 
>>> concept that such packets represent - an identity “claim”. Such a 
>>> claim can be explicit (there’s a User ID with a self-signature over 
>>> it), or implicit (I found this in an Autocrypt header). We don’t 
>>> need to get into such details in this draft, but I think it’s good 
>>> to keep them in mind when drawing up suitably generic language.
>>
>> I see the following potential technical problem: Eve has an existing 
>> key with a single user ID [email protected]. Alice trusts that Eve 
>> rightfully owns this email address. Now at some point Eve creates a 
>> new key and sets the Replacement Key Subpackets in both the the old 
>> and the new key such that there is key equivalence established 
>> between them. The new key also happens to contain the User ID 
>> [email protected]. Will Alice now trust that Eve also controls this 
>> email address?
>>
> Equivalence doesn’t mean that all userids are valid, it means that 
> they are *as* valid for one primary key as they are for any other in 
> the equivalence set. If [email protected] is claimed by one cert but not 
> verified, then a receiving implementation will treat it as claimed but 
> not verified by the other cert of the set.
>
> Put another way, Alice does not “trust eve’s key” - she trusts a 
> particular userid claimed by eve’s key.
>
> Does that help?

Yeah, of course it makes sense to model trust on a per-user-ID basis. In 
my view that is something that could be mentioned in the document in at 
least one sentence (even though it might be obvious to a sensible 
implementer).

Best regards,
Falko

>
> A
>
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