Wanted to share a quick blog post (see link) playing around with a couple methods of validating data origin and integrity without blindly relying on public CAs.
It’s sort of a follow-up-to-a-follow-up on an earlier post about using Cloudlfare proxies to selfhost personal sites or services, but it really applies more to TLS and public CAs in general.
If there’s a concern that an adversary can rewrite hashes then why is there not a concern the public key could also be rewritten and the hashes signed with the fake key?
Could mTLS be used instead to force the browser to validate the correct cert?
Not directly, but I believe mTLS would break if the traffic was intercepted/altered, so it sort of works to test the connection.
mTLS requires installing a certificate on the client device, though. If you’re able to do that, then you’re also able to pin the correct cert or install a custom CA. This would be the “enterprise” solution, as far as I know, but doesn’t work well for public sites, since you can’t always configure your end-users devices.
Edit: mTLS is still very useful, though. I use it to secure some of my services. It just doesn’t solve this specific problem.
I’ll add: mTLS would only break because the client certs are typically signed by a private CA and the host is configured to only trust that specific CA (similar to the enterprise solution I referenced in the post).
If, for some reason, the host was configured to trust all of the typical public CAs, then mTLS would theoretically share the same problem.
