Hi Rich, When I say “authoritative”, I mean it in the true TLS sense, in the way that I believe the ECH draft also suggests and requires.
In other words, the middlebox serves a cert to the client that is cryptographically valid for the said public name of the client facing server. How can that be when the client facing server guards its private key properly? By re-signing the server certificate on the middlebox with a private key, local to the middle box only, for which the corresponding certificate has been installed in the trust store of the client, before sending it on to the client. Only after the original server certificate has been validated properly on the middlebox, of course. Message digests being managed accordingly/appropriately. That is a very typical setup for most (all?) TLS inspection devices (next gen firewalls and such). Thus this part of ECH, requiring the middlebox to be authoritative for the server, is well understood and prolifically exercised in inspected TLS sessions today. What is new is that these connections can now fail/close, in the “securely disabling ECH” case, and the onus is on the TLS client, not the application, to retry the connection without ECH. I am after such a client, if one exists already. Thank you. Sent from my phone > On Oct 7, 2022, at 11:41 AM, Salz, Rich <[email protected]> wrote: > > > Client <-> Middlebox <-> Client-facing server <-> Backend server > > With "Middlebox" really meaning a middlebox like a firewall or similar. > > The middlebox is not allowed to modify traffic between the client and the > server. Doing so would mean that the packets the client sent are not the ones > that the server received, and the two message digests would disagree. (If > you think about things, it *has* to be this way, otherwise TLS would not be > able to provide integrity guarantees.) > > From the draft, ECH seems to be designed to still allow successful TLS > connection establishment if the encrypted_client_hello extension is dropped > from the ClientHello on a conforming middlebox. Provided that the middlebox > is authoritative for the client-facing server's public name, as > reported/delivered by DNS to the client. We can assume that this is the case > here. > > I do not understand what you mean by this. The word “authoritative” is used > to mean that it has a certificate and keypair and can do TLS termination. DNS > giving the client a particular IP address is not authoritative. It can be > confusing because DNS terminology uses authoritative to mean that a > particular entity can prepare data used for DNS responses. But it is not > authoritative in the TLS sense. > > I think your questions can be answered with those two overall corrections > above. If not, please continue the thread. (And feel free to repost from > your note since I trimmed for brevity.)
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