On Sun, Jan 06, 2019 at 05:48:46AM +0530, Viruthagiri Thirumavalavan wrote:
> > This adds complexity, without solving any problems. I'm afraid
> > this proposal has no merit.
> > * The attacker can just as easily block connections to port 26,
> > as filter out STARTTLS.
> > * This in no way addresses the authentication issues.
>
> I already addressed both issues in the document. Refer "Deprecation" and
> "Security Considerations" section. My proposal is all about deprecating
> "Plain Text" in port 25.
I stand by the "has no merit" assessment. Nobody is going to turn
off port 25 support overnight. This proposal would need to be able
to coëxist with the traditional port 25 SMTP service, but then it is
trivially vulnerable to the same downgrade attacks that it ostensibly
tries to avoid by using "implicit TLS" instead of "STARTTLS".
Indeed STARTTLS gives MTAs the opportunity to decline service prior
to completing the TLS handshake, which can be useful when the client
is e.g. listed on an RBL, or is performing TLS handshakes at an
excessive rate.
Secure MTA-to-MTA SMTP does not require abandoning STARTTLS. Rather,
MTA-to-MTA SMTP security requires a downgrade-resistant signal of
when TLS is mandatory, and a robust means to authenticate the peer.
Neither of these is facilitated by this proposal.
--
Viktor.
P.S. Everyone is of course free to post to the list some plausibly
(or even vaguely) on-topic content, and all posts made in good faith
are welcome. That said, I will not make any further comments in
this thread, as it rather looks like a dead-end.
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