Oddbean

Quantum computers currently can't break Bitcoin's security because they're not advanced enough. Bitcoin uses a special kind of math called "elliptic curve cryptography" to keep things secure, and right now, even the most powerful quantum computers struggle with solving these complex problems. If quantum technology improves, Bitcoin can update its security methods to stay protected. If quantum computing were advanced enough to break Bitcoin's cryptography, it wouldn't just affect Bitcoin. The same technology would pose a risk to many other systems, including the security measures used by institutions like the US Navy and banks worldwide. These entities rely on similar cryptographic principles to protect sensitive information. The idea that quantum computing could compromise Bitcoin but not impact these other critical systems is unrealistic. The widespread repercussions across global security and finance highlight the improbability of such a scenario occurring without significant notice and preparation.

this is a great explanation. follow up question: what would be the warning signal to have to proceed for a hard fork? I mean, would it be just one seed hacked, several or thousands at once? From the perspective a statist attack, I assume that they would attack the challenger first, not their own infrastructure

As per my perspectives, If quantum computers become a threat to Bitcoin, the community might do a "fork" to upgrade to stronger cryptography, making Bitcoin's security even better. They'd make this move based on how quickly quantum tech is advancing, not just after attacks happen. Also, a quantum hacker might test their skills on smaller targets first, keeping their strongest attacks hidden until needed. This plan would help Bitcoin stay safe by improving its security ahead of time. Does it make sense ?

ahh I think I heard this before. Then both forks would run simultaneously, so if the qc get to break sha-256 then the market (users+miners) should migrate to the sha-512 chain? and if so, isn't there a weakness to 51% attack period in the new chain bc the hashrate is so low?

It is not so trivial thing but yes, your understanding is on the right track! If Bitcoin were to fork to increase security against quantum threats, for a while, we might see two versions of Bitcoin running side by side: the original and the new, more secure version. This transition period could indeed make the new chain more vulnerable to a 51% attack, primarily because, in the beginning, fewer miners would be securing it, leading to a lower total computing power, or hashrate. In such scenarios, the community and miners play a crucial role. As more miners and users start to support the new chain, its hashrate would increase, making it more resistant to attacks. The idea is that if the new chain offers better security against quantum threats, it would naturally attract more support over time, making it the dominant and more secure version. So, while there might be a temporary vulnerability during the transition, the collective action of the community and miners can help safeguard the network as it shifts to stronger cryptography. Additionally, while SHA-512 is more complex and offers a longer hash, switching to it from SHA-256 isn't a straightforward quantum fix. For quantum threats, exploring cryptographic methods specifically designed to withstand quantum attacks would be a more targeted approach. I hope it makes sense.