Subject: Security concerns around co-locating TLS and non-secure on same port (WGLC: draft-ietf-tsvwg-iana-ports-08)

From: Magnus Westerlund <[email-masked]>
Date: Mon, 08 Nov 2010 11:14:35 +0800

TLS experts,

There currently a WG last call ongoing in on the IANA Procedures for the
Management of the Service Name and Transport Protocol Port Number
Registry update document.
https://datatracker.ietf.org/doc/draft-ietf-tsvwg-iana-ports/

A WG last call comment on this document was raised by Paul Hoffman:
http://www.ietf.org/mail-archive/web/tsvwg/current/msg10305.html

My summary of that comment is that STARTTLS for SMTP (RFC 3207) has
shown to have some security issues, be complexer to implement than using
two ports and thus less popular. Thus the registration rules should be
less restrictive in assigning an additional port for TLS version of
services/applications/protocols.

The downside of less restrictive port allocation rules is that the port
space will be consumed at a higher rate. Thus there is need to determine
what is the most suitable trade-off here.

Clearly if the security issues are serious when one multiplex TLS and
non-secured version of the protocol on the same port we must allow such
port allocations. However if the issues are minor and the primarily
issue is implementation complexity then saving the limited port space is
probably more important.

Your input into these questions would be very appreciated.

Thanks

Magnus Westerlund

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From: Michael D'Errico <[email-masked]>
Date: Sun, 07 Nov 2010 20:44:23 -0800

Here's a radical idea for IANA -- STOP REGISTERING UNENCRYPTED PROTOCOLS!

The days of unencrypted anything are nearing an end, so there should be
only one port assigned that uses TLS.  The day is coming when businesses
will be forced to stop sending email that is unencrypted.  Their privacy
policies will demand it.  SMTP will either get a don't_forward_this_
without_encryption option, or it will perish.

Mike

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From: Geoffrey Keating <[email-masked]>
Date: 08 Nov 2010 11:40:29 -0800

> https://datatracker.ietf.org/doc/draft-ietf-tsvwg-iana-ports/
..
> services/applications/protocols.
...
> Your input into these questions would be very appreciated.

There are also security issues when two ports are used: how can an
application choose which port to communicate over?  Paul mentions the
list of security issues in RFC 3207, but each of these corresponds to
a similar issue in a two-port solution.  Eventually the RFC (and
similar specifications of other protocols) comes down to

"The decision about whether acceptable authentication or privacy was
   achieved is made locally, is implementation-dependent, and is
   beyond the scope of this document."

and in practise this leads to at least one, and sometimes more, of these:

1. Implementations which do not interoperate, because one requires
   security and the other does not implement it,

2. Automatically falling back to insecure communications when secure
   communications cannot be achieved, even if this is due to an
   attacker's denial-of-service, or

3. Asking the user questions that the user does not understand or for
   which the user cannot know the answer ("Is example.com supposed to
   have secure email?").

So, I think there are very limited additional concerns for a
single-port approach over a two-port approach, but there are
significant problems with both, and if implementation complexity and
interoperability is a concern it could and probably should be
addressed by specifying that TLS is always used.