Re: [dane] provisioning assumptions, was PGP security models, was Summary

["John Levine" <[e-mail]>]

>The other common use problem is not being able to delete keys, so you end
>up using a keyserver, get a (verified by WoT) key and then in response
>you get a plaintext message saying "I forgot my passphrase so i cannot
>delete/revoke my old key". With DNS, you can remove the key from DNS
>without needing the private key or passphrase to it.

There's a whole bunch of unsupported assumptions here about how mail
and DNS provisioning systems work.

While there's often a way to recover your account if you lose your
password, at large mail systems they don't work very well,
particularly if the account's been compromised and taken over by a bad
guy, which happens thousands of times a day.  (I know people at Yahoo
whose full time jobs are to deal with this.)  Even without a
compromise, it's often more hassle than it's worth to recover the
account, so you create a new one and the old one sits there
unused--that's why I'm [e-mail] rather than jrlevine.

Also, this introduces a downgrade attack.  User creates a key, gets
lots of WoT signatures, publishes it through key servers and DANE.
Bad guy takes over the account, publishes a new key with no
signatures.  According to sec 5.2 of the draft, a mail sender looks up
the key, finds they disagree, and the verification fails.  Now what?
The draft suggests dumping the question on the MUA user, which we know
is never a good idea.  As likely as not a naive user would pick the
newer key, the one that says "USE THIS KEY OLD ONE WAS STOLEN."

Finally, if the problem with existing key servers is that they won't
delete dead keys, that does not strike me as an insoluble problem.
Talk to the people who run them, suggest they add an "it's dead"
button that sends a confirmation message to the address in the key and
when confirmed, deletes the key.  The security risk is small, it is
just as secure as the DANE approach (with the advantage that existing
PGP clients work unchanged), and we're all done.

R's,
John