Selfhosted

which is still there if you are not using lets encrypt, because they can strongarm them to make a fake cert for your domain, and install a proxy repackaging HTTPS traffic with the fake certificate. all browsers trust the lets encrypt root certificate, so they won't see anything suspicious.

the only thing there today to detect this (but not avoid) is certificate transparency logs. all modern certificates are required to be added to this log, for the CA to remain compliant. but browsers are not checking the logs, that would be a lot of additional traffic and how do they decide if a certificate was created maliciously? also, lets encrypt could afford being noncompliant, browser vendors can't realistically just distrust their root certificate, many sites would become inaccessible.

Edit: no, it doesn't. Looking at the comments below, it's public key crypto.

Original comment:

The problem is that if that is your threat model, then the VPS provider, ISP, and literally everything between you and letsencrypt can pull a conpromised key fro letsencrypt.

This actually happened btw, an xmpp server was attacked this way, they compromised not the server itself, but the VPS provider MITMed their traffic: https://www.devever.net/~hl/xmpp-incident

If your threat model involves this, then the only solution is Tor, which eliminates these requirements of trust.

Yep, that's what I described and any CA accepted by the client can do it

Yes, the private key never leaves your machine.

You send them a certificate signing request with your public key, they put their verification stamp on it and send it to you.

The only part they have to play is verifying that your certificate is trusted by a root certificate.

The CA cannot decypt: they don't have the secret key which only the server has. When requesting a new certificate from the CA, the server generated a secret key (aka private key) and then generated a derived public key that goes into a Certificate Signing Request (CSR). The CSR is what the CA receives, not the secret key, and then the CA returns the certificate file to the server, which has been endorsed by the CA and thus trusted by the user base.

Phrased another way, a certificate is the instrument that confirms that a purported public key can in-fact be safely used, and that no MITM attack is happening (assuming you trust the CA that signed the cert). But once you've confirmed the public key, the rest of the cryptography is public key cryptography, meaning the secrecy of the secret key is the whole game.

A MITM doesn't require decrypting. It just requires telling a convincing enough lie to each side of a conversation that they think they're talking to the other party. Then you end up encrypting to their key which they can just read. That's different from breaking the encryption.

Are you sure they can’t decrypt?

No, and none of the state actors who do that kind of stuff will ever tell you. Watch The Imitation Game for a good/bad time and some context.

If you had a break for the modern crypto schemes and published it right now you would shut down all digital commerce, a lot of the spy traffic if not most of it^1^, and nothing could be started back up again until everything was redone from scratch. Best hope would be that the post quantum algorithms^2^ the cryptographers have aren't succeptible to whatever you did to break the existing algorithms. It'd take a bit to get the software implementations and keys in place, etc. The hardware stuff would take longer.

• [1] The stuff using One Time Pads would still be fine, but its limitations wouldn't take the place all of all the rest of it.
• [2] The rollout of post quantum algorithms is going on now on a more accelerated schedule than originally planned.

The certificate is only used for authentication. The actual data is encrypted with a temporary symmetric key that is generated via a diffie-hellman exchange

Even if they had your private key they still wouldn't be able to decrypt the data

They don't have your private key