Re: [TLS] The future of external PSK in TLS 1.3

Filippo Valsorda <filippo@ml.filippo.io> Sat, 19 September 2020 16:02 UTC

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Date: Sat, 19 Sep 2020 18:00:00 +0200
From: "Filippo Valsorda" <filippo@ml.filippo.io>
To: tls@ietf.org
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Subject: Re: [TLS] The future of external PSK in TLS 1.3
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2020-09-19 13:48 GMT+02:00 Peter Gutmann <pgut001@cs.auckland.ac.nz>nz>:
> John Mattsson <john.mattsson=40ericsson.com@dmarc.ietf.org> writes:
> 
> >Looking at the IANA TLS registry, I am surprised to see that psk_dhe_ke and
> >especially psk_ke are both marked as RECOMMENDED. If used in the initial
> >handshake, both modes have severe privacy problems,
> 
> PSK is used a fair bit in SCADA.  There are no privacy problems there.  So
> just because there's a concern for one specific environment doesn't mean it
> should be banned for any use.  In particular, I think if a specific industry
> has a particular concern, they should profile it for use in that industry but
> not require that everyone else change their behaviour.

Indeed, if the SCADA industry has a particular need, they should profile TLS for use in that industry, and not require we change the recommendation for the open Internet.

Setting Recommended to N is not "banning" anything, it's saying it "has not been through the IETF consensus process, has limited applicability, or is intended only for specific use cases". SCADA sounds like a pretty specific use case.

I don't have a strong opinion on psk_dhe_ke, but I see no reason psk_ke wouldn't be marked N like all suites lacking PFS.