So you didn't need to "break" BB84, you just needed to sit there with a microphone and you could read out the whole key. It doesn't matter how much physics guarantees the safety of your encryption if you go and tell the adversary what your key is.

For BB84, that deeply did not matter, it was a proof of principle. But in the 41 years since, that problem — that side channels exist — keeps getting forgotten.

A bit over a decade ago, my partner @crazy4pi314 got their PhD in large part by showing that if you shine an *even brighter* laser into commercial QKD systems, you can even destroy the detectors they use to prevent that kind of attack. That attack involves things like putting 60W of laser power down a telecom fiber, but they came up with novel ways of doing so, despite that being wildly out of safety specs.

It's very fun work.

@xgranade @psistarpsiii
This was the one I could find quickly, ft. my supervisor proving the beam is there by burning his had lol
https://youtu.be/ORaBbEM9M4E?si=2m62ljW3PIbeakLS

In this we were working with 1440nm light at ~30W CW (testing ranges of 20-60W). The fiber is just standard telecom optical fiber and we had to try really hard to get it to fail here, specifically grinding the end on a shiny table to start the fuse. Normally they start from excess bending/cracks/thermal damage