What Google’s quantum computing breakthrough means for Bitcoin. Two weeks ago, Google released Willow, a breakthrough quantum computing chip that reduces its errors as it scales up in size. Although its 105 qubits (quantum computational units) are far short of the millions needed to crack modern cryptography, many are wondering if this advance in scalability threatens Bitcoin. The worry is fair. The blockchain, Bitcoin’s public ledger that allows it to serve as a decentralized currency, relies on two sets of numerical keys each holder has: a public one that everyone can see and a private one. These keys are like signatures the user attaches to transactions. A well-known quantum algorithm could use public keys to deduce private ones—like using your public signature to figure out all your passwords. The problem goes far beyond Bitcoin. Virtually all digital assets are protected by similar cryptographic techniques designed to resist classical computers, not quantum ones. Your bank account’s not going to be in any better shape than Bitcoin, if a bad actor somehow developed a practical quantum computer and attacked the financial system. Gold bars would be safe. Fortunately, cryptographers have a variety of methods known to be resistant to quantum computing. They just haven’t been standardized and implemented yet because they haven’t been needed; with Willow, this work will likely accelerate. The trick is to pose the computer a problem with more dimensions than it can keep up with. Even with its qubits, which can do more computations than classical bits because they can exist in more states, there’s only so much a quantum computer can do. One promising class of quantum-resistant algorithms uses lattice problems, which involve grids of points in multi-dimensional space—basically, if you make the cryptography maze large enough, even a quantum computer gets lost, no matter how fast it can run. Google’s new chip doesn’t directly endanger Bitcoin, and the problem it poses affects all digital assets. But it does make the quantum threat more acute. It will probably propel the world’s efforts to adopt post-quantum cryptography, with the Bitcoin community leading the way by integrating quantum-resistant protocols in the blockchain.
