Saw a comment on a banking thread that said that Quantum Computing will kill crypto, I assume because it would be able to edit the blockchain and thus killing the entire point of bitcoin, but how exactly would it do this? How does it work and why does it mean all current encryption would become useless?
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Quantum computers can factorize numbers much faster than traditional computers.
This would enable them to sign break the elliptic curve cryptography part of bitcoin.
This has been known for a long time by the bitcoin community.
Bitcoin is not fixed to using ECC. The plan is to change Elliptic curve cryptography for any other public/private key system which is not vulnerable.
The reason they do not do it now is that every replacement would take up more space on the blockchain.
Do you happen to know when quantum computers will become a thing that can be used outside major corporations? The videos I watched looked to be something that was still a long way away.
There needs to be consumer utility for them to be attempted. I haven't heard of a practical use for normal people for quantum computers.
Neural renderers could be one, but such a software doesn't even exist as a prototype.
Or a war with a major power. Decryption tech would instantly become a priority.
For consumers?
No, but that's not relevant.
Most of the technology we have today ultimately came about in the middle of WW2. Everything from computers to radar to jet and rocket engines, to nuclear weapons and nuclear reactors.
A war with a major power would see tens of billions dumped into breaking encryption as quickly as possible, and once that tech exists, it will spread, and it will be used everywhere.
The computer needs 4000 qubits.
currently the largest has 256 qubits
https://phys.org/news/2021-07-team-quantum-simulator-qubits-largest.html
What's stopping them from plugging in 16 of them together to make 4000 qbits.
Physics.
No one knows that. For all we know the technology exists within governments, and they're just not letting on.
The theory with quantum computing is that rather than have to calculate millions or billions of possible keys and check each one in turn to see if you've found the correct one, you simply point your quantum box at the task and it calculates all possibilities simultaneously. You then simply pick out the one that did the trick.
Not theory. There are production chips / computers at 50+ Qubits.
Notice the coincidence of Q with Qubits.
It's a cool fact about the universe that will blow your mind: in some ways, the universe doesn't appear to be "computational" - meaning, it doesn't act like a computer.
One interpretation for the things we see at the quantum level is the Many Worlds interpretation. This is the idea that there are literally an infinite number of alternate universes, with infinitely more of them being created from moment to moment.
Got a pair of sunglasses? Okay, the lenses are polarized. When a photon reflects off a surface, the photon becomes polarized, and when that photon encounters a polarized lens, there's a chance it will be blocked by the lens, and a chance it will go through. This is why your sunglasses reduce the glare of light reflected off the windshields of cars.
The Many Worlds hypothesis says that when the photon becomes polarized, it doesn't actually "decide" at that moment which way it's polarized. And it wont ever bother to decide unless someone measures it (like for example with a polarized filter). At the moment when it's measured, according to this theory, the entire universe splits in two, and there's a universe where the measurement went one way and a whole other universe where it went the other way. There are literally two different versions of you, the observer - one in the universe where the photon made it through, and one where it was blocked.
And this is an interpretation that scientists take seriously because there's real evidence for it. You can probably see how this could not possibly be computational - it wouldn't be possible to build a computer that actually simulated this. You can't build a computer that actually does all the universes.
I don't have a really good practical understanding of quantum computers. I know that they very carefully keep particles in the wave state (they don't measure the particles). They let the particles become entangled with other particles, and they measure those. And somehow, they are able to use this to get results in a single operation that, in a classical computer would require brute force (you'd have to check every possibility).
A filter isn't a measurement. The photon will remain as probability until observed by a conscious mind.
There isn't evidence. Scientists affirm many worlds because they are against the idea of consciousness solidifying reality.
A filter is a measurement.
The photon is blocked or passes through regardless of the presence of a conscious mind. The video you got this from, with the creepy animated guy, lied to you. Also, "What the *bleep* do we know" lied to you.
There is evidence.
And you reject many worlds because you like the idea of consciousness solidifying reality. What you need to do is propose an experiment that has a different result if a consciousness is involved than if no consciousness is involved.
Not really. Going single-core to multi-core each core is still calculating one key at a time. This means it's not terribly difficult to simply crank up the key length - add 8 bits and you've got a thousand times as much work to do, which makes the gains from running 8 cores diminish somewhat.
Similarly, GPUs, while offering substantial parallelisation, merely move a balance point that can be redressed by using longer keys.
The point with QM is that you run all of the numbers at once. As I understand it, a lot of the cleverness is in the "simply pick out the one that did the trick" step, as otherwise, yes, you are just running through your impressively-calculated solutions one at a time.
It means you can only factor one large number at a time. IOW, find one person's private key at time.
By compromising SHA-256.
The entirety of bitcoin's scarcity relies on the security of SHA-2. This is why I don't have any, because I have NEVER believed that SHA-2 was secure for anything more than data-in-flight.
I acknowledge that, yeah, I left some money on the table there. Bitcoin certainly demonstrated its potential. But I don't trust SHA-2 for durable storage.
So most computing is on and off. The quantum computer has the ability to read more than that. The rest is dressage.
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With 897 physical qubits (75 logical qubits) a dwave was able to factor 200099 in 3.5 seconds. They need 12x more physical because literally anything interacting with the bits ruins the computation (runs at 25 millikelvin, nearly absolute zero).
So using the same method to factor a 600 digit prime instead of a 6 digit prime sounds pretty far off.
And when it does happen, with some kind of breakthrough hardware design, they're not going to be stealing your $1k bitcoin wallet they're going to keep it secret as long as possible so they can use it on really important stuff.