Giving someone, other than those managing the endpoints, the ability to disable a security feature like ECH is problematic.
If I read your email correctly then I believe that’s what you are suggesting. I hope I am missing something. Ciao Hannes From: TLS <tls-boun...@ietf.org> On Behalf Of Safe Browsing Sent: Wednesday, October 19, 2022 4:56 AM To: Eric Rescorla <e...@rtfm.com> Cc: TLS@ietf.org Subject: Re: [TLS] Securely disabling ECH Hi Eric, Picking up on your (earlier) reply here. Though it would be possible to adjust the setting in browsers (disabling ECH), this is not an ideal/sufficient method of disabling ECH. Some reasons it is not sufficient: - Not all TLS clients are browsers - Not all browsers (or other TLS clients) may implement this ability - In a multi-browser environment it means that it needs to be configured in more than one place, each using a different method of achieving the same (cumbersome) - even worse if there are other, non-browser, ECH supporting clients present for which ECH needs to be disabled It seems therefore that the ideal place to achieve this is within the protocol itself. Making ECH disabling client agnostic. The draft does consider this by allowing ECH to be disabled - as discussed in this thread. Albeit at the cost of an extra round trip. However, the connection retry logic in the presence of ECH disabling is currently optional. The draft states, in Section 8.2: “ this may trigger the retry logic” It seems this text must change to: “ this MUST trigger the retry logic” In order to ensure functional connections in a TLS client agnostic manner, in the presence of protocol level ECH disabling. I would appreciate your thoughts/input. On Oct 8, 2022, at 7:41 PM, Eric Rescorla <e...@rtfm.com<mailto:e...@rtfm.com>> wrote: If you are able to install a new trust anchor, then you should be able to use the enterprise configuration mechanisms in browsers to disable ECH. -Ekr On Fri, Oct 7, 2022 at 8:40 PM Safe Browsing <safebrowsing...@gmail.com<mailto:safebrowsing...@gmail.com>> wrote: 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 <rs...@akamai.com<mailto:rs...@akamai.com>> 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.) _______________________________________________ TLS mailing list TLS@ietf.org<mailto:TLS@ietf.org> https://www.ietf.org/mailman/listinfo/tls IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. 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