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Re: [TLS] Can flags be responded to with an extension?

Benjamin Kaduk <bkaduk@akamai.com> Wed, 13 April 2022 22:51 UTC

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Date: Wed, 13 Apr 2022 15:51:31 -0700
From: Benjamin Kaduk <bkaduk@akamai.com>
To: Eric Rescorla <ekr@rtfm.com>
CC: "<tls@ietf.org>" <tls@ietf.org>
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Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/40t8pBBKBiJuSp_WPS_xkVrGphA>
Subject: Re: [TLS] Can flags be responded to with an extension?
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On Wed, Apr 13, 2022 at 10:56:49AM -0700, Eric Rescorla wrote:
> Consider the case where the client wants to offer some capability that
> the server then responds to with real data, rather than just an
> acknowledgement.
> 
> For instance, supposing the SCT extension from RFC 6962 did not exist,
> the client would want to indicate support in CH and the server would
> send the SCT in CERT, but this extension would need to be non-empty
> and hence not a flag. draft-ietf-tls-tlsflags-09 seems a bit
> uncelar on this point (unless I'm missing it) but I think we
> should explicitly allow it.

In my head this was already disallowed.  I couldn't swear to whether
we actually talked about it previously or not, though.

-Ben

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