Comment by adzm
11 hours ago
It's possible symmetric encryption may never really be defeated by anything other than brute force. The exchange of the ephemeral key really is the important part, as you mention. Thankfully looks like we are getting closer to full adoption of post quantum TLS... but that doesn't help recorded communications before very recently. Scary thought.
Looks like 70% of cloudflare requests are using post-quantum TLS! https://radar.cloudflare.com/post-quantum
This makes me wonder why we aren't using pre-shared keys as one extra layer of defense.
The idea would be to use an existing connection (established via normal TLS) to agree upon and exchange a pre-shared key. For subsequent connections, that key would be incorporated as one extra input to the key derivation function, and a new key would be derived.
This would make TLS more secure against adversaries who can break asymmetric encryption (now or later) and monitor some of your communications, but who do not have access to all of your communications. If you managed to get on an unmonitored network even once (foreign hotel WiFi, coffee shop without a wiretap), and securely establish a PSK there, all future interactions would be inaccessible to an adversary who can't break symmetric crypto.