[spec] Certificate trust

Hello,

I have been using lagrange for a few months to browse Gemini, and I 
realize that I?m already making a habit of ignoring certificate mismatch 
warnings, and blindly trusting any certificate that shows.

The certificate trust is one of the weak point of the current 
specification I think, and it would need to be clarified.

Firstly, there is the idea of TOFU, but it does not say on which part of 
the certificate the TOFU works (some people consider it?s the whole 
certificate, some only the fingerprint), and it does not say how much the 
certificate needs to be valid (I?ve seen on the ML some people considering 
that a wrong domain in a certificate and a past expiration date should be 
ignored by clients). Reading the specification it appears that it 
recommends using fingerprint and to consider past expiration date invalid.
Secondly, there is the good old CA system, nowadays mostly using 
letsencrypt. It seems badly supported in most clients which still use TOFU 
in this case and will complain at each renewal.
A third possibility I think would be to use DANE and base validation on 
the DNS system, but I?ve not seen anyone advocating this, is there 
anything wrong with that idea?

I?m failing to see how TOFU can provide any security, especially if there 
is no way to announce a renewal by sending both new and old cert or 
something, there is a MITM possibility at each renewal. The only TOFU 
example I?ve seen cited is openssh, which seems offtopic because you 
usually do not ssh into random machine on the internet by following links 
like you do with Gemini.

C?me

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