[openpgp] Re: Call for adoption of draft-gallagher-openpgp-replacementkey

[Falko Strenzke <[e-mail]>]

Am 30.04.24 um 17:47 schrieb Daniel Huigens:
>> Yes, I did consider that we could define a “trust equivalence” signature that would be closer conceptually (and cryptographically) to a subkey binding signature than to a certification. But I’m not sure that belongs here either, and it certainly opens a lot more questions.
> But I'm not sure we need a new signature type for that; we could just
> interpret a third-party certification with type ID 0x13 (Positive
> certification of a User ID and Public-Key packet) made by a key with
> the same User ID as having that meaning, for example? Then we don't
> need any new mechanism for this.

In the new draft such a mechanism is now specified. Section "4.2 Graph 
topology", however, restricts this mechanism to only be applicable to 
any two keys and not more.

I tend to disagree with the restriction for any key to be able to either 
point to a replacement key or identify itself as a replacement key for 
another key. If one publishes one after another 3 generations of a key, 
say A, B, and then C, then at first key B might contain the RKS to 
identify itself as the replacement key for A and thus establish key 
equivalence binding between A and B. When afterwards publishing C, in 
order for B to indicate C as its replacement key, the key equivalence 
binding between A and B has to be lifted. That seems like a potentially 
disturbing artifact, since a user who still only holds the key A will 
now not see key equivalence binding with B for no convincing logical 
reason. Instead, the graph should be traversable from A to B, then it 
should be checked if C can be used as the replacement and if not, B 
should be checked (or maybe in the other order). For this purpose, I 
think B should be able to hold one or two RKS in order to indicate both 
relations.

- Falko

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