On Tue, Oct 18, 2022 at 8:56 PM Safe Browsing <safebrowsing...@gmail.com> wrote:
> 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” > This language change would not make sense. The context for "this may trigger the retry logic" in section 8.2 offers two options. The sentence structure is "Depending on whether X, this may Y or Z", i.e. if X is resolved one way, then the client does Y, otherwise it does Z. Changing the "may" to "MUST" would result in stating "this MUST trigger the retry logic described in Section 6.1.6 or result in a connection failure", which doesn't really make sense, and wouldn't have the goal you'd like, since a connection failure instead of retry logic would satisfy the MUST. If your server is authoritative for the public name, then the behavior you care about is described in section 8.1. I suspect most implementations of ECH will implement the retry logic, as the misconfigurations and deployment concerns described in section 8.1 are an inevitability, and implementing the retry logic avoids connection failures that would occur without it. I doubt that adding a MUST would make someone more likely to implement 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> 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> > 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> 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 >> https://www.ietf.org/mailman/listinfo/tls >> > _______________________________________________ > TLS mailing list > TLS@ietf.org > https://www.ietf.org/mailman/listinfo/tls >
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