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[spec] Certificate trust

Stephane Bortzmeyer stephane at sources.org

Mon Mar 1 09:17:49 GMT 2021

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On Sun, Feb 28, 2021 at 08:27:26PM +0100, Côme Chilliet <come at chilliet.eu> wrote a message of 32 lines which said:

The certificate trust is one of the weak point of the current

specification I think, and it would need to be clarified.

I agree with your statement. With the new issue tracking system thatSean configured, this is ticket #5<https://gitlab.com/gemini-specification/protocol/-/issues/5>.

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.

More precisely, each renewal, BY DEFAULT. But Let's Encrypt lets yourequest that we keep the public key, and then TOFU will still work iffit acts on the public key only.

If you use the ACME client dehydrated, this is in the configuration file:

PRIVATE_KEY_RENEW="no"

With the ACME client certbot, this is an option on the command-line:

--reuse-key

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?

This is certainly the best solution, technicallyspeaking. Unfortunately, adding DANE support to your Gemini clienttypically requires some effort, the existing libraries are typicallynot sufficient. (Full disclosure: I did not even add DANE support tomy own Gemini client, despites the fact I'm strongly pro-DANE.)

Also, the Internet is very ossified by broken middleboxes (typicallyfirewalls but not only them) and TLSA requests may be blocked (or,worse, any DNSSEC use, which DANE requires). This is something to keepin mind.

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.

I fully agree. TOFU is great for SSH but Gemini is completelydifferent.