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

[Hannes Tschofenig <[e-mail]>]

Hi Carrick,

Can you justify your reasoning?

The challenge I have with the work on IoT in the IETF that the preferences for pretty much everything changes on a regular basis.

I don't see a problem that requires a change. In fact, I have just posted a mail to the UTA list that gives an overview of the implementation status of embedded TLS stacks and PSK-based ciphersuites are widely implemented.

Ciao
Hannes

From: TLS <[e-mail]> On Behalf Of Carrick Bartle
Sent: Monday, September 21, 2020 5:31 AM
To: Filippo Valsorda <[e-mail]>
Cc: [e-mail]
Subject: Re: [TLS] The future of external PSK in TLS 1.3

I'm also fine with marking psk_ke as not recommended to be consistent with the non-PFS ciphers, but there are plenty of valid use cases that justify keeping dhe_psk_ke as recommended for external PSKs. Several of these use cases are detailed in draft-ietf-tls-external-psk-guidance-00.



On Sep 19, 2020, at 9:00 AM, Filippo Valsorda <[e-mail]<mailto:[e-mail]>> wrote:

2020-09-19 13:48 GMT+02:00 Peter Gutmann <[e-mail]<mailto:[e-mail]>>:
John Mattsson <john.mattsson=[e-mail]<mailto:[e-mail]>> 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.
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