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Ok, so there's a time window where it's possible to prove that you were the sender. And if I use a qualified timestamp service to sign all messages arriving in

Ok, so there's a time window where it's possible to prove that you were the sender. And if I use a qualified timestamp service to sign all messages arriving in my inbox, then I can prove that you were the sender indefinitely.

deleted 2y ago
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kstrauser 2y ago
Something like that, as long as you can also prove I hadn’t published the key prior to that. If I publish at random times and to random URL, that may be challenging.
- freedomben 2y ago
  Yes, but then it also encroaches on ability to verify that you were the sender when receiving the original email. Basically, unless the recipient also checks whether the current DKIM key has been published, then they can't trust it because it may be published. If it's being published at random times and to a random URL, then it's nearly impossible to actually check. So I agree that it brings deniability, but I don't agree that it still meets the original purpose of verifying the sender.
  - kstrauser 2y ago
    That’s all true, but I bet 99.99% of all email is delivered within a minute or so of being send. There are exceptions, of course, but in practice the whole thing is pretty fast. So there’s some threat modeling, too. Are you trying to email someone highly adversarial? Maybe you’re at a law office or such and that’s the case! This wouldn’t help a lot there. Not everyone is immediately forwarding all inbound mails to a timestamping service though. (I don’t have skin in this game, so I’ll probably duck out after this. I don’t have opinions on whether publishing old DKIM keys is good or bad.)
    - jcgl 2y ago
      > I bet 99.99% of all email is delivered within a minute or so of being send No doubt that is true. However, given the total volume of email, even that tiny, tiny remaining fraction still represents actual mail with legitimate use-cases. So it's good to bear that fact in mind and not roughly implement 80-20 stuff that tramples on those.

deleted 2y ago

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kstrauser 2y ago

Something like that, as long as you can also prove I hadn’t published the key prior to that. If I publish at random times and to random URL, that may be challenging.

freedomben 2y ago
Yes, but then it also encroaches on ability to verify that you were the sender when receiving the original email. Basically, unless the recipient also checks whether the current DKIM key has been published, then they can't trust it because it may be published. If it's being published at random times and to a random URL, then it's nearly impossible to actually check. So I agree that it brings deniability, but I don't agree that it still meets the original purpose of verifying the sender.
- kstrauser 2y ago
  That’s all true, but I bet 99.99% of all email is delivered within a minute or so of being send. There are exceptions, of course, but in practice the whole thing is pretty fast. So there’s some threat modeling, too. Are you trying to email someone highly adversarial? Maybe you’re at a law office or such and that’s the case! This wouldn’t help a lot there. Not everyone is immediately forwarding all inbound mails to a timestamping service though. (I don’t have skin in this game, so I’ll probably duck out after this. I don’t have opinions on whether publishing old DKIM keys is good or bad.)
  - jcgl 2y ago
    > I bet 99.99% of all email is delivered within a minute or so of being send No doubt that is true. However, given the total volume of email, even that tiny, tiny remaining fraction still represents actual mail with legitimate use-cases. So it's good to bear that fact in mind and not roughly implement 80-20 stuff that tramples on those.