Re: [ietf-smtp] ALPN

John Levine <johnl@taugh.com> Thu, 29 July 2021 03:07 UTC

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Date: Wed, 28 Jul 2021 23:07:40 -0400
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From: John Levine <johnl@taugh.com>
To: ietf-smtp@ietf.org
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Subject: Re: [ietf-smtp] ALPN
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It appears that Claus Assmann  <ietf-smtp@ietf.org> said:
>On Wed, Jul 28, 2021, Alexey Melnikov wrote:
>
>> I think having separate allocations for them would be clean design.
>
>Stupid question: what are the differences in the actual protocol
>between SMTP and SUBMIT?

The port numbers, and the fact that 465 does TLS on connnect.  Other than that, nothing.

Since SMTP doesn't do TLS on connect I have trouble imagining an attack that an ALPN
wouldn't 

>A possible hack is to redirect a HTTP connection to an SMTP server:
>different ports / different protocols.
>ALPN is supposed to prevent such "cross protocol" attacks.

You can certainly point a browser at http://your.ser.ver:25/something but again
I have trouble imagining an actual threat, and even more trouble imagning
one where an ALPN would make any difference.

R's,
John