Could A Sufficiently Powerful Computer Bring Down Bitcoin?

Could a sufficiently powerful computer bring down Bitcoin?

- Ian Evenden

Anyone who is not heartily sick of the words ‘blockchain’, ‘crypto’, and ‘NFT’ (and, indeed, mentions of quantum computing in these pages) may be interested to hear that, in a few years’ time, the whole thing might go away.

It’ll probably be replaced by something worse, of course, but the argument over the subject is interesting. Could a sufficiently powerful quantum computer, one that’s not been invented as yet, bring the whole blockchain network down around our ankles?

It’s easy, and often fun, to attribute remarkable powers to inventions of the future. Imagining VR that links itself directly to your visual cortex does not make it a reality, but quantum computers exist in the same way VR helmets do: the ones we know about are very early models that could all do with some improvement. And the ones we don’t know about? Well, who knows what the world’s governments are up to?

Wild speculation aside, the problem here is asymmetric cryptography. Two keys are generated, and they have a mathematical relationship – the public key can be derived from the private key, but not the other way around. The public key is just that – public. It’s used by anyone who wants to encrypt information that only you can read. The asymmetric bit means that running the encrypted data through the public key backwards (as you would with something like Enigma, for example) doesn’t decrypt it: for that you need the private key which you don’t tell anyone, even your psychiatrist. From this system the blockchain, Bitcoin, NFTs and a market worth over $100 billion were born.