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> Ok, my GPG example was wrong. And yes, you got me, I'm not a professional cryptographer. But can you address the point? You said "once counterparties have aut

> Ok, my GPG example was wrong. And yes, you got me, I'm not a professional cryptographer. But can you address the point? You said "once counterparties have authenticated each other's messages, the legitimate need for authentication is gone". I provided a counter-example ... I think the person you're talking to thinks this is very obvious and thus isn't stating it explicitly, but in the special case where you want an email to include non-repudiation, such as for a purchase receipt, the sender should just add non-repudiation to it in the form of a signature that's intended for that. Simple.

baobabKoodaa 6y ago
> the sender should just add non-repudiation to it in the form of a signature that's intended for that. Simple. Ok, but this does not magically happen if Google publishes and rotates their DKIM keys. People will continue to use email for everything, but now emails can no longer be authenticated by third parties.
- hamburglar 6y ago
  I think the entire point is that non-repudiation shouldn't just magically happen unless intended, so yes, this is by design, and anyone who wants to send a signed email should explicitly send a signed email.
  - baobabKoodaa 6y ago
    > I think the entire point is that non-repudiation shouldn't just magically happen unless intended, so yes, this is by design, and anyone who wants to send a signed email should explicitly send a signed email. Let's not pretend that the world would move away from email if Google made this change. We both know that's not going to happen. Given that, can you explain why you think the world would be a better place when emails can be repudiated? When emails can be not be repudiated, innocent people can be framed for saying/doing things that they didn't do. DKIM protects innocent people from being framed. DKIM also protects innocent people against guilty people who commit frauds or other crime.
    - cakoose 6y ago
      First, "innocent people can be framed" is not that simple. Without non-repudiation, you don't automatically get to frame someone for whatever. You need to provide the usual (non-DKIM) evidence of whatever you're claiming. And even with non-repudiation, you can still try and frame someone. Not having the DKIM signature might be suspicious in some circumstances, but it doesn't eliminate the possibility. Second, "innocent" is not that simple. I don't want my private communication to become public, or publicly verifiable. That doesn't mean I'm not "innocent". This is not a fringe concept: https://en.wikipedia.org/wiki/Nothing_to_hide_argument https://en.wikipedia.org/wiki/Nothing_to_hide_argument "Give me six lines written by the most honest man in the world, and I will find enough in them to hang him." - Cardinal Richelieu
      - baobabKoodaa 6y ago
        > I don't want my private communication to become public, or publicly verifiable. That doesn't mean I'm not "innocent". This is not a fringe concept: https://en.wikipedia.org/wiki/Nothing_to_hide_argument https://en.wikipedia.org/wiki/Nothing_to_hide_argument Yes, I agree we should have secure private messengers. But that has nothing to do with this discussion. First off, email is not a secure private messenger. Second, email would not become "more secure" by removing the accidental, partial non-repudiation that DKIM provides. Third, this comment chain that you are replying in right now, is about whether there exists any legitimate need for a third party to authenticate emails with DKIM after the emails have been sent. tptacek claimed that no such legitimate need exists. I've been arguing against this with a specific counter-example.
        hamburglar 6y ago
        "with DKIM" is the part of your argument you've failed to back up. Yes, you have a counter-example that requires authenticated emails. You don't have one that requires authenticating emails with DKIM.
        baobabKoodaa 6y ago

baobabKoodaa 6y ago

> the sender should just add non-repudiation to it in the form of a signature that's intended for that. Simple. Ok, but this does not magically happen if Google publishes and rotates their DKIM keys. People will continue to use email for everything, but now emails can no longer be authenticated by third parties.

hamburglar 6y ago
I think the entire point is that non-repudiation shouldn't just magically happen unless intended, so yes, this is by design, and anyone who wants to send a signed email should explicitly send a signed email.
- baobabKoodaa 6y ago
  > I think the entire point is that non-repudiation shouldn't just magically happen unless intended, so yes, this is by design, and anyone who wants to send a signed email should explicitly send a signed email. Let's not pretend that the world would move away from email if Google made this change. We both know that's not going to happen. Given that, can you explain why you think the world would be a better place when emails can be repudiated? When emails can be not be repudiated, innocent people can be framed for saying/doing things that they didn't do. DKIM protects innocent people from being framed. DKIM also protects innocent people against guilty people who commit frauds or other crime.
  - cakoose 6y ago
    First, "innocent people can be framed" is not that simple. Without non-repudiation, you don't automatically get to frame someone for whatever. You need to provide the usual (non-DKIM) evidence of whatever you're claiming. And even with non-repudiation, you can still try and frame someone. Not having the DKIM signature might be suspicious in some circumstances, but it doesn't eliminate the possibility. Second, "innocent" is not that simple. I don't want my private communication to become public, or publicly verifiable. That doesn't mean I'm not "innocent". This is not a fringe concept: https://en.wikipedia.org/wiki/Nothing_to_hide_argument https://en.wikipedia.org/wiki/Nothing_to_hide_argument "Give me six lines written by the most honest man in the world, and I will find enough in them to hang him." - Cardinal Richelieu
    - baobabKoodaa 6y ago
      > I don't want my private communication to become public, or publicly verifiable. That doesn't mean I'm not "innocent". This is not a fringe concept: https://en.wikipedia.org/wiki/Nothing_to_hide_argument https://en.wikipedia.org/wiki/Nothing_to_hide_argument Yes, I agree we should have secure private messengers. But that has nothing to do with this discussion. First off, email is not a secure private messenger. Second, email would not become "more secure" by removing the accidental, partial non-repudiation that DKIM provides. Third, this comment chain that you are replying in right now, is about whether there exists any legitimate need for a third party to authenticate emails with DKIM after the emails have been sent. tptacek claimed that no such legitimate need exists. I've been arguing against this with a specific counter-example.
      - hamburglar 6y ago
        "with DKIM" is the part of your argument you've failed to back up. Yes, you have a counter-example that requires authenticated emails. You don't have one that requires authenticating emails with DKIM.
        baobabKoodaa 6y ago