Subject: [TLS] Question about draft-thomson-tls-sic

From: Watson Ladd <[email-masked]>
Date: Tue, 23 Jul 2019 17:22:41 -0700

Suppose the following sequence of events happen:

1: A CA uses a new intermediate for reasons (no longer cross-signing, etc.)
2: A site gets a certificate from the new intermediate.
3: An older firefox version connects and thinks it knows all the
certificates in the world.

This would seem to break and it wasn't clear to me how this would be
handled. Though as Martin points out this extension is merely codification
of an occasional practice, so maybe this case does actually work out.

Sincerely,
Watson Ladd

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From: Adam Langley <[email-masked]>
Date: Tue, 23 Jul 2019 18:15:10 -0700

> of an occasional practice, so maybe this case does actually work out.

I think the client would have to fall back and retry the TLS connection
without requesting that intermediates be omitted. In general, I think this
is the only reliable answer as AIA-chasing doesn't always work. (Either the
AIA server can be down, or the chain can be from a private CA that doesn't
support AIA.)

Cheers

AGL