How Quantum Computing Can Compromise Bitcoin Security in Under 10 Minutes

The first part of this series delved into the physics underlying quantum computing, but understanding how it works is not the same as knowing how it can be used to steal bitcoin. To grasp the latter, one must comprehend what quantum computers attack and where the weakness in bitcoin's security lies. This piece begins by examining bitcoin's encryption, specifically how it utilizes elliptic curve cryptography to verify ownership, and then proceeds to explain how a quantum algorithm can break this encryption. Bitcoin's security is based on a one-way function, where a private key is used to generate a public key, but it's virtually impossible for classical computers to reverse this process. However, a quantum algorithm known as Shor's algorithm can efficiently solve this problem, thereby breaking the encryption. The recent Google paper has reduced the estimated number of qubits required to run Shor's algorithm against bitcoin's elliptic curve, making the threat more immediate. The paper introduces a practical attack scenario where parts of the algorithm can be precomputed, leaving the quantum computer in a state ready to finish the calculation once a target public key appears. This reduces the time needed to derive a private key to about nine minutes, which is close to bitcoin's average block confirmation time. The implications are significant, with approximately 6.9 million bitcoin potentially vulnerable to such an attack, either through a race against the clock when a transaction is broadcast or through an 'at-rest' attack on already exposed public keys.