this post was submitted on 02 Aug 2026
6 points (60.0% liked)

Showerthoughts

43184 readers
134 users here now

A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. The most popular seem to be lighthearted clever little truths, hidden in daily life.

Here are some examples to inspire your own showerthoughts:

Rules

  1. All posts must be showerthoughts
  2. The entire showerthought must be in the title
  3. No politics
    • If your topic is in a grey area, please phrase it to emphasize the fascinating aspects, not the dramatic aspects. You can do this by avoiding overly politicized terms such as "capitalism" and "communism". If you must make comparisons, you can say something is different without saying something is better/worse.
    • A good place for politics is c/politicaldiscussion
  4. Posts must be original/unique
  5. Adhere to Lemmy's Code of Conduct and the TOS

If you made it this far, showerthoughts is accepting new mods. This community is generally tame so its not a lot of work, but having a few more mods would help reports get addressed a little sooner.

Whats it like to be a mod? Reports just show up as messages in your Lemmy inbox, and if a different mod has already addressed the report, the message goes away and you never worry about it.

founded 3 years ago
MODERATORS
vatlark@lemmy.world
forkball@lemmy.world
SuperEars@lemmy.world
6
The promise of quantum computing breaking the cryptography is a lie. (lemmy.world)
submitted 5 days ago by BlackLaZoR@lemmy.world to c/showerthoughts@lemmy.world
34 comments fedilink hide all child comments
 

The whole promise is that reversible computation is theoretically free (in quantum information theory) , quantum computer can exploit it by using quantum superposition to brute force 256bit key (and larger) in a single computation cycle.

There's a massive fundamental flaw in the reasoning behind this.

It's the second law of thermodynamics - entropy always increases. While computation is free, reversal of entropy isn't. What we're being promised is a 21st century version of perpetual motion machine.

Additional explanation:

Think about private key as low entropy, and public key as high entropy. Owner of the private key has cheat code in the form of missing information which allows reversing the entropy of public key.

However in order to break the cryptography you have to reverse public key back into private key without having access to it. The regualr way is to search for flaws in the cryptography scheme that allow reasoning about missing information and consecutively - private key recovery.

But if you do a brute force attack you are 100% forced to pay full thermodynamical price of reversing the entropy. And 2^256 is way, way more than you could ever afford. Even Planck scale values multiplied by that number grow into universe size and beyond.

In summary, quantum computing can skip time component of brute forcing a key, but it can't skip the energy costs. So it will never happen.

you are viewing a single comment's thread
view the rest of the comments
[–] maxwellfire@lemmy.world 4 points 4 days ago* (last edited 4 days ago)

I think you're almost right about the high level principles, you've just forgotten that entropy scales as the log of the combinations not linearly.

So the entropy of a 128 bit key is not 2^128, it's just 128 and therefore the fundamental limit on the cost required to recover it that you're talking about is very small.

See landauer limit (which isn't quite the same thing since it's about irreversible computers which some quantum computers might not be, but gets at the idea of there being an energy cost to have information)

I believe the specifics of your thoughts about entropy of public vs private keys is also incorrect but not necessary to the core of what you're saying.