There is another aspect to the MSMD not really addressed by the Levine
proposal, or at least directly.
MSMD is making a guarantee about private delivery (or not at all) in an
ecosystem where many of
the SMTP servers do not support STARTTLS. If the Levine proposal uses
DKIM's public key form DNS TXT, ...
No problem, it doesn't. My plan is to use a key from a distinguished
DNS name which was _encrypt._domainkey.<domain> (to reuse tools people
already have to publish DKIM keys) but could be anything else.
The existence of that record is the signal that the recipient domain
is prepared to decrypt and unwrap pickled mail.
DKIM can be removed from the proposal without harm to main concepts.
In the likely initial uses for MSMD, likely the sender and recipient would
already have a relationship
that requires this feature e.g. corporate or consumer financial so probably
would wouldn't treat
such notifications as spam. That said it can be dropped without harm to
main proposal, and
restored if that's found to be useful later.
If they already know each other, now I'm wondering what the practical
advantage is over S/MIME.
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