The Quantum Threat to Bitcoin: How a Powerful Computer Can Steal Your Cryptocurrency in Under 10 Minutes

The first part of this series explored the principles of quantum computing, but understanding how it works is only half the story. To grasp the threat it poses to bitcoin, we need to examine what it's attacking: the encryption that secures bitcoin transactions. This piece will dissect how bitcoin's security is built, where its weaknesses lie, and the nine-minute window identified by Google's recent quantum computing paper. Bitcoin relies on elliptic curve cryptography, a system that utilizes a pair of keys: a private key, which is a secret number, and a public key derived from the private key through a mathematical operation. This process can be thought of as a one-way map, where starting from a known point, taking a certain number of steps leads to the public key, but reversing the process to find the private key is virtually impossible for classical computers. However, a quantum algorithm known as Shor's algorithm can efficiently solve this problem, breaking the encryption. The algorithm works by converting the problem into finding the period of a function, which quantum computers can solve using superposition, entanglement, and interference. Despite Shor's algorithm being known for over 30 years, the lack of a sufficiently powerful quantum computer has kept bitcoin safe. Recent estimates by Google suggest that the number of qubits required to run Shor's algorithm against bitcoin's encryption might be lower than previously thought, potentially putting the cryptocurrency at risk. The introduction of a practical attack scenario, where parts of the calculation can be precomputed, waiting for a target public key to appear, changes the dynamics of the threat. If a quantum computer can derive a private key within the nine-minute window before a transaction is confirmed, it could potentially steal bitcoin. With approximately 6.9 million bitcoin already vulnerable due to exposed public keys, the threat is significant.