[DNSOP] Re: Proposal for opportunistic transport signaling from authoritative servers

[Joe Abley <[e-mail]>]

On 24 Jun 2025, at 21:38, Ben Schwartz <bemasc=[e-mail]> wrote:

> 1. An attacker could strip the SVCB record and its RRSIG, resulting in an ordinary delegation response that would be accepted and used without encryption.

True. A client that didn't find a record could query for it which would give it the ability to validate any non-existence, but that sounds like a lot of pointless queries in the situation where the majority of zones don't have this kind of thing deployed (when most referrals don't include a courtesy SVCB).

> 2. This is a child-side record, and so presumably also a child-side RRSIG, but the validator may not yet have the child's DNSKEYs.  Fetching those keys (in order to validate the transport configuration) would create additional delay before the query could be sent.

That additional delay can be amortised over the lifetime in the cache of those records needed to provide a chain of trust though. A validator is going to have to do that work at some point.  

> 3. The parent-side logic to serve this RRSIG, and the coordination channels to get it there, seem complicated.

I guess. It seems approximately as complicated as CNAME flattening which is pretty common.

> Assuming it is signed by the ZSK, this also breaks a usual rule of not having parent-side content depend on the child ZSK.

The referral can be processed without it (by using other transports) so I'm not sure it's a dependency. 

The downgrade attack seems worth thinking about. I'm not sure how much we need to care about the other things. 


Joe