On 12/6/22 3:22 PM, [email protected] wrote:
That's not true in all cases. Spam and phishing slips through
filters, etc, regularly and doing forensics may happen well past
delivery windows. Part of DKIM is a "blame me" mechanism. If you
remove the signature how do they know they are actually responsible?
Perhaps the domain can keep the signatures separate, just not when
sent out to the MUA. Or we can figure out something more creative.
. And even if you remove the signature, there is a lot of other
evidence that a leaked email provides. DKIM with Her Emails made a
pretty watertight case that they were real, but even without it it
would have been really hard to disclaim them, especially if people
get access to the receiving domain's logs in a legal setting.
Not all versions of adversarial attribution are done publicly or in a
legal setting, and journalistic authentication is always possible.
This is materially different than not offering any protection to users
at all, and offering authenticated proof of private communications. A
user may be able to disclaim specific messages, for example, even if
others appear to be correct (“that message was modified!”)
I (and others) wrote a usenix paper on the subject. Perhaps taking a
look at the paper’s motivation will be helpful in understanding our
complaint with how DKIM works now:
https://www.usenix.org/conference/usenixsecurity21/presentation/specter-keyforge
Frankly using Her Emails as a motivation to do something is rather
pointless. The valid DKIM signature was icing on the cake. The cake
would have been eaten with our without it though. Nobody actually cared
about whether it could standup in court or not. Even I for years didn't
know that DKIM was part of the picture but it really didn't matter one
way or the other whether I thought they were legit or not.
Mike
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