 Just a couple of days ago, Google claimed that it has reached quantum supremacy. How do you think this will affect mining and the cryptocurrency world in general? I love the way that they named their success in quantum computing. Quantum supremacy, it sounds so amazing, but in fact, it's not really that amazing. Some great marketing there caused a whole ripple of fear all across the technology industry, as people misunderstood what quantum supremacy means. Up to now, quantum computers could solve problems that classical computers could also solve. They might solve them a bit faster, but it was really difficult to see if, in fact, the quantum effects were giving a significant advantage to the quantum computer, to the point where a classical system is simply unable to solve that in any meaningful amount of time. Quantum supremacy, as Google calls it, is simply the first time they demonstrated a solution to a problem that was solved with a quantum computer in a reasonable amount of time, and with a classical computer that would take tens of thousands of years. Therefore, that shows that the quantum effects being operated in this quantum computer really confer a significant advantage in computation. It's no longer a question of, was this really a quantum result, or was it just a slight optimization on a classical result? This is a whole other realm of computing, because of course now you can do something with a quantum computer that a classical computer cannot do in any practical sense because of the time difference. That's what they mean by quantum supremacy. However, we're still talking about 100-something qubits without error correction, and this is a really, really important point. In fact, doing quantum computing with error correction is a much higher bar, difficulty if you like, than doing quantum computing without error correction. For cryptography, you actually need error corrected bits, and you need thousands of them. You need thousands of qubits to be doing quantum corrected calculations in order to break something like ECDSA, to be able to reverse a public key to a private key on the elliptic curve, for example. What is the effect on mining in the cryptocurrency world in general? Zip, buccas, nada, nothing really happens. Quantum supremacy, what Google described, is demonstrating the practical applicability of quantum computers to certain classes of problems. Those classes of problems are not the same class of problems we're talking about when we talk about breaking cryptography. That's a really good thing because the problem isn't really Bitcoin. If we get quantum computers that can do thousands of qubits with error correction and consistent results, we have a much bigger problem. The bigger problem we have is that the entire world's classified communications, confidential communications, financial systems, all depend on classical cryptography today. We would need to upgrade all of that in order to make it quantum resistant. If anything, many of those systems, these legacy systems, are a lot more difficult to upgrade than an open public, open-source blockchain like Bitcoin is in terms of its signatures. In fact, we're already seeing a proposal for a new signature system called Schnorr that is being introduced as part of Segwit v1, hopefully in the next year or so. But while Schnorr isn't quantum resistant, it is demonstrating the capability of developers and the ecosystem as a whole to upgrade and switch the digital signature algorithm. Therefore, we can imagine a time when quantum computing starts approaching the practicality of breaking classical cryptography, at which point we do upgrade and we will need to upgrade the digital signature algorithm. We can see now that that's possible. It's something that practically can be done within the ecosystem and it will be done probably in the next year for Schnorr signatures. Now, the other thing, of course, is to realize there's a difference between quantum computing being applied to digital signatures and quantum computing being applied to hashing. Hashing algorithms are fundamentally different from digital signature algorithms. While the street logarithm problem that is at the core of digital signature algorithms is, in fact, very approachable by a quantum algorithm, a quantum solution, and if you have a quantum computer with enough bits, you will be able to break it thoroughly, reverse it in very, very short time. That does not apply equally to hashes. So, hashes do not use or are not based on the discrete logarithm problem. They're not based on factorization. They're not based on these one-way functions we see with digital signatures. Instead, they use a series of permutations, binary shifts, and things like that, which are not actually that easy to develop a quantum algorithm to break. So, hashes are a lot less sensitive to quantum computers than digital signature algorithms. And just there, you might notice this little trick that Satoshi introduced, which was to never present the public key naked if you like to the system until you're spending from that address, and instead present a double-hashed version of that called the Bitcoin address. This is a genius little trick, which not only provides level of abstraction, but it actually provides a level of protection against weaknesses in the elliptic curve algorithm. Weaknesses that can be introduced through a malformed signature, such as reusing a random number in a signature, or weaknesses that are introduced because of quantum computing, or vulnerabilities in the algorithm for digital signatures that are discovered later. No matter what the weakness might be, if you follow the best practice, which is to use a Bitcoin address once and only once, and to immediately spend all the funds in it the first time you sign and never sign for that address again, what you get is a much higher level of protection because the moment the public key is recorded on the blockchain, it's recorded because the funds just got moved and are no longer in that address. The address effectively is empty, zero balance. So the only time the public key is shown is when, even if you exploit it, you get nothing because there's no money in it anymore. And that's a really smart trick because even if quantum computing gets the point where digital signatures can be compromised, now what that means is that someone would have to be able to compromise the digital signature in a time between you transmitting a transaction to the network and it getting confirmed and the money spent and then break it, sign a different transaction and double spend it in less than 10 minutes. So it actually puts another layer of difficulty, if you like, on top of the public key and digital signature algorithm itself. So this question comes up a lot, so I'm just going to make it very clear. A lot of people keep getting worried about quantum computing. We are nowhere near the level of quantum computing that would be needed. There is a small possibility that some intelligence agencies are a decade or more ahead in their ability to do quantum computing. If that is the case, which we can't really tell, then they might be able to do things in the next decade to break Bitcoin's digital signature algorithm. But if they have a secret that important, they're unlikely to use it to attack something that's not that important. When that secret is also important for attacking confidential and secured and classified communications of military adversaries, or even the keys that control the nuclear weapons systems in order to disarm them and turn them off. So that's the kind of secret you keep very, very close and you don't reveal it by attacking some Bitcoiners just to cause some damage and a cryptocurrency. More likely, however, we are still at least a decade, if not several decades from quantum computing being able to break digital signature algorithms. And more importantly, if we get closer to that point, the digital signature algorithm and even the hashing algorithm can be modified to make it more quantum resistant and more secure against quantum attacks. Eventually, you get to the point where quantum computing is a commercial reality for everyone, where everyone has the ability to use commercially available quantum computers on the desktop, on the laptop, maybe on the smartphone and or whatever other device. At that point, you can use a quantum computer to do quantum encryption that cannot be broken by a quantum computer trying to do quantum decryption. And therefore, if everybody has quantum computing, the threat goes away. The threat only exists if very few people have very powerful quantum computers and nobody has any ability to change the algorithms, which is a rather extreme and unlikely scenario in any way. So I'm not worried about quantum computing. It's a fascinating topic to talk about. It's fun to speculate. But in practical terms, these are not the threats that the Bitcoin faces. There are much more practical ways to attack Bitcoin and other cryptocurrencies than these exotic types of threats like quantum computing.