On 4/4/24 12:43 AM, Jay Acuna wrote:
On Thu, Apr 4, 2024 at 1:23 AM Adam Brenner via NANOG <nanog@nanog.org> wrote: ..
It seems to me that if msn.com is going to include DKIM headers in their outgoing email, they should also publish their DKIM public key. If they are not going to publish their DKIM public key, then they should not include DKIM headers in their outgoing email. Microsoft can still sign the message, Even if the signature cannot be verified because they have not yet published the Public Key, for whatever reason. That is a partial/incomplete implementation of DKIM then.
There is one potential reason a site might want to do this which is to essentially invalidate signatures from a non-repudiation standpoint. Simply unpublishing the key while not 100% foolproof is essentially saying "we don't take responsibility for mail signed with this key anymore" -- sort of like the expirey tag in the header but with attitude. The entire kerfuffle about Her Emails (ie Hillary's email server) was in part about the fact that the mail on it could still be verified and thus not denied. After, there were calls for providers to publish their private keys on a regular basis but that went nowhere that I've heard of. That's probably not what's going on here -- maybe they just botched a key rollover -- but it still amusing to me that we got non-repudiation along for the ride [*]. Mike [*] while DKIM only speaks at the domain level and not an individual account, if providers always require submission auth before signing that seems pretty airtight to me