On 18/11/2020 22:17, Michael Thomas wrote:
On 11/18/20 2:04 PM, Stephen Farrell wrote:Hiya, On 18/11/2020 21:51, Michael Thomas wrote:On 11/18/20 1:45 PM, John R Levine wrote:Why isn't just deleting/replacing the selector sufficient? It's not as definitive but it's a lot simpler.On Wed, 18 Nov 2020, Ned Freed wrote:That said, a mechanism for publishing/expiring DKIM private keys is somethingthe IETF might want to standardize.I've started to publish my old private keys since I rotate every month but I agree a standard way to tell people where to look would be nice.Publishing the private key enables various forms of denyability - if someone claims msg1 is original anyone with access to the private can produce a msg2 that seems as cryptographically correct but is clearly bogus (e.g. containing lottery numbers that post-date message timestamps).Yes, i acknowledge that above albeit obliquely. What i don't see is how you align providers goals' with individual users' goals.
My guess is that email service providers that are concerned about potential leakage of message store content would be motivated to do this so as to re-assure their users and/or maybe help avoid future liability (financial or moral).
Yes an adversary could have gotten an independent signed timestamp on msg1 before the private was published but that seems low probability.
It really depends on the worth of the data, right? LEA would certainly do such a thing if they were serveilling somebody.
Sure. The main adversary I had in mind for this mechanism would be a message (store) leaker, not LEAs. I guess the idea could be ineffective or even counterproductive with other threat models, not sure - but would need checking out, for sure.
I forget who said that they were surprised about lack of key rotation, but color me completely unsurprised. This is just inertia 101. Maybe large ESP's might get around to automating key rotation, but for the vast majority enterprise this is going to be pretty low down the priority list, and more likely an anti-goal as tracking whether their employees are misbehaving is a feature not a bug.I'd support development of such a standard if it had a good chance of deployment as I think it'd also encourage key rotation.
Agreed. If, however, publishing old private keys is seen as a way to reduce potential liability, then that might motivate rotation. (That's my guess, but only a guess.) Cheers, S.
Mike
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