Topic: Google claims breakthrough in Quantum computing (Read 857 times)

But if quantum computing actually happens, then won’t regular passwords for bank accounts and emails, etc. be most at risk? I mean, there’s a lot more at risk than just Bitcoin and at least Bitcoin private keys have a bunch of digits.

have fun
no point arguing no more.

well you can continue with your google search for average joe stuff...
ill continue programming

have fun with your studies, hope you can catch up

by the way google quantum computers quarternary

qubits actually have 4 states

binary has 2 states
0-1

qubit is base 4 or otherwise known as quarternary logic (as oppose to binary logic)
0  1
  X
2  3

oh and bit is about single object/symbol
you can have binary(2) bit
quarternary(4) bit
hexidecimal(16) bit

research: "4 quantum numbers"

In quantum mechanics, the principal quantum number (symbolized n) is one of four quantum numbers assigned to all electrons in an atom to describe that electron's state.

in quantum there is 4
0 is off 1 is 'kinda on' 2 is mostly on and 3 is on
0 is no 1 is maybe  2 is mostly  and 3 is yes
0 is false 1 is false unless  2 is true unless and 3 is true

google has the technology of 4 states and now is trying to code how to use it.
mostly they are dealing with DNA you know GTAC annd having fun with that as binary systems aint good at 4 state things in a 2 state limiting system

There are only 2 states contributing to the superposition, 0 and 1.

You mean 4 because the probability amplitudes are complex numbers and each have 2 degrees of freedom? So 2x2 =4? ... But probability is amplitude squared (the Born rule)... so we are back to 2.

its 0123 no 01.

Not really. It's still just 1s and 0s in quantum computing - the difference is superposition, the fact that in QC multiple states exist simultaneously. So as you increase the number of qubits (x), the processing power increases exponentially, 2^x.

Honestly, I figured breaking mining would break bitcoin more effectively than hacking addresses.

Hi all   I thought I’d try to summarise Bitcoin's vulnerabilities to Quantum Computers, as well as some potential defences, and get it all in one post. Apologies for the wall of text, but hopefully it is useful...


Mining can potentially be much quicker with QCs.
The current PoW difficulty system can be exploited by a Quantum Computer using Grover’s algorithm to drastically reduce the number of computational steps required to solve the problem. The theorised advantage that a quantum computer (or parallelised QCs) have over classical computers is a couple of orders of magnitude, so ~x100 easier to mine. This isn’t necessarily a game-changer, as this QC speed advantage is likely to be some years away, by which time classical computers will surely have increased speed to reduce the QC advantage significantly. It is worth remembering that QCs aren’t going up against run-of-the-mill standard equipment here, but rather against the very fast ASICs that have been set up specifically for mining.

Re-used BTC addresses are 100% vulnerable to QCs.
Address Re-Use. Simply, any address that is re-used is 100% vulnerable because a QC can use Shor’s algorithm to break public-key cryptography. This is a quantum algorithm designed specifically to solve for prime factors. As with Grover’s algorithm, the key is in dramatically reducing the number of computational steps required to solve the problem. The upshot is that for any known public key, a QC can use Shor’s approach to derive the private key. The vulnerability cannot be overstated here. Any re-used address is utterly insecure.

Processed (accepted) transactions are theoretically somewhat vulnerable to QCs.
Theoretically possible because the QC can derive private keys from used addresses. In practice however processed transactions are likely to be quite secure as QCs would need to out-hash the network to double spend.

Unprocessed (pending) transactions are extremely vulnerable to QCs.
As above, a QC can derive a private key from a public key. So for any unprocessed transaction, a QC attacker can obtain the private key and then create their own transaction whilst offering a much higher fee, so that the attacker’s transaction gets onto the blockchain first, ahead of the genuine transaction. So block interval and QC speed are both crucial here – it all depends on whether or not the a QC can hack the key more quickly than the block is processed.


Possible defences...

Defences using classical computers.

• Modify the PoW system such that QCs don’t have any advantage over classical computers. Defending PoW is not as important as defending signatures (as above), because PoW is less vulnerable. However various approaches that can protect PoW against QCs are under development, such as Cuckoo Cycle, Momentum and Equihash.
• Modify the signature system to prevent easy derivation of private keys. Again, various approaches are under development, which use some pretty esoteric maths. There are hash-based approaches such as XMSS and SPHINCS, but more promising (as far as I can tell) are the lattice-based approaches such as Dilithium, which I think is already used by Komodo.
  

Defences using quantum computers.
As I’ve said a few times, I’m more of a bumbling enthusiast than an expert, but exploiting quantum properties to defend against QC attack seems to me a very good idea. In theory properties such as entanglement and the uncertainty principle can offer an unbreakable defence. Again, people are busy researching this area. There are some quite astonishing ideas out there, such as this one.


I’ll leave it there. Apologies for all the external links, but hopefully this has summarised a few things.

qubits actually have 4 states

binary has 2 states
0-1

qubit is base 4 or otherwise known as quarternary logic (as oppose to binary logic)
0  1
  X
2  3

qbits have 3 states

Bitcoin in danger?


https://www.forbes.com/sites/darrynpollock/2019/09/24/googles-quantum-computing-breakthrough-brings-blockchain-resistance-into-the-spotlight-again/

Did you mean complexity of 2^128, as that is the complexity of cracking bitcoin with the best known non QC algorithm. And QC could not use that algorithm, so it would probably need the full 256 qubits to do the calculations.

...

Bitcoin in danger?

I thought it broke at a complexity of 128^3 from what was previously discussed last time (I have no links though). Isn't this old news? I'm sure we saw the same headline about 6 months ago...

Forbes and the financial Times seem really awful sources nowadays, perhaps their editor bought stocks in Google or something..., There seemed to be a consensus that the sha256 hashing algorithm was quantum proof too - people don't want to act until the nsa release standards of quantum proof encryption so we're stuck in the hope that's the case anyway...

... I figured breaking mining would break bitcoin more effectively than hacking addresses.

Sha256... I guess it'd be the entropy of the hash. I just assumed sha256 had 256 bits of entropy. That's probably a horrible assumption considering the 256 is the digest.

I thought it broke at a complexity of 128^3 from what was previously discussed last time...

Forbes and the financial Times seem really awful sources nowadays, ...

Where do you get that number from? Just curious.

Is not about blocks mined, is about keys broken. Full collapse, hard fork, market stop...

Wouldn't a quantum computer need 256 qubits to break bitcoin?

Also, if there's a strange amount of blocks being mined by a new entity, can't we just fork with a new algorithm (and fuck over ASIC manufacturers at the same time )

This week, news has emerged that Google has made a recent quantum computing breakthrough, achieving quantum supremacy. It is being reported that Google, using a quantum computer, managed to perform a calculation in just over three minutes that would take the world's most powerful supercomputer 10,000 years.
...

According to Gizmodo, it has been long known that Google has been testing a 72-qubit device called Bristlecone with which it hoped to achieve quantum supremacy and the initial report from the Financial Times says that the supremacy experiment was instead performed with a 53-qubit processor codenamed Sycamore.

...

"Blockchains won't be ready for such a breakthrough. Since transaction history is the backbone of blockchains, such an improvement in quantum computing could be catastrophic for the whole transaction history," added the CTO. "There is an extra layer of protection with Bitcoin's double hashing but assuming a quantum computer is capable of Shor on secp256k1 it's safe to assume it's also capable of Grover256. Also, we don't know bounds for SHA regarding quantum circuits."
...