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Re: [TLS] Authenticating incompatible protocols

Ben Schwartz <bemasc@google.com> Wed, 15 July 2020 20:52 UTC

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From: Ben Schwartz <bemasc@google.com>
Date: Wed, 15 Jul 2020 16:52:35 -0400
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To: Martin Thomson <mt@lowentropy.net>
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Subject: Re: [TLS] Authenticating incompatible protocols
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On Wed, Jul 15, 2020 at 2:25 AM Martin Thomson <mt@lowentropy.net> wrote:
...

> you need to configure discovery methods and your TLS stacks with the same
> information (though your TLS configuration can be more conservative in
> terms of advertising a subset of what can be discovered, so that
> deployments can be staged).


If there are multiple ways to reach your server (multiple applicable
scopes), you have to be even more conservative: you can only advertise the
_intersection_ of supported protocols from all possible scopes.  The
ClientHello doesn't tell the server which scope the client has.

Basically, I think this draft should probably either name the scope or be
specific to SVCB, to avoid cases where the scope is ambiguous.  Naming the
scope, and providing a scope identifier meaning "IP and port number", would
often be sufficient for secure QUIC upgrade without SVCB, at the cost of
some conceptual complexity.

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