Re: [TLS] I-D Action: draft-rescorla-tls-ctls-04.txt

Martin Thomson <mt@lowentropy.net> Tue, 10 March 2020 04:27 UTC

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Date: Tue, 10 Mar 2020 15:27:30 +1100
From: "Martin Thomson" <mt@lowentropy.net>
To: tls@ietf.org
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Subject: Re: [TLS] I-D Action: draft-rescorla-tls-ctls-04.txt
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On Tue, Mar 10, 2020, at 14:17, Watson Ladd wrote:
> One thing I noticed from my reading is there is no gain from knowing
> an extension will be present if one doesn't also know the value.

That is only true if the extension has a value.  (See also flags)

> I could imagine SNI being very useful to include, and knowing the order
> of extension values permits their omission, keeping only the length.

I believe that is the idea: put the extension at a fixed location so that you don't have to signal its type, just its value.

> This does mean very little freedom to add new unknown extensions.

I don't think that is necessarily true.