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

The first part of this series delved into the physics behind quantum computing, explaining how these machines differ from regular computers. However, understanding how quantum computers work is not the same as knowing how they can be used to steal bitcoin. To grasp the latter, one must comprehend what a quantum computer attacks and how bitcoin's security is structured, including its vulnerabilities. This article begins with an examination of bitcoin's encryption method, known as elliptic curve cryptography, and progresses to discuss how a quantum algorithm can break this encryption in approximately nine minutes, as outlined in a recent paper by Google. The security of bitcoin is based on a one-way function, where a private key, where the private key is a secret number and the public key is derived from it through a mathematical operation on a specific curve. This one-way function is virtually unbreakable by classical computers due to the immense time it would take to reverse the process. However, a quantum algorithm known as Shor's algorithm can efficiently solve this problem, potentially allowing a quantum computer to derive a private key from a public key. The algorithm utilizes the principles of superposition, entanglement, and interference to find the period of a function, which is crucial for breaking the encryption. Although Shor's algorithm has been known for over 30 years, its implementation has been hindered by the requirement for a large number of stable qubits. A recent paper by Google has significantly reduced the estimated number of qubits needed, making the threat more realistic. The paper introduced a practical attack scenario where parts of the algorithm can be precomputed, leaving only the final steps to be completed once a target public key is identified. This reduces the time needed to derive a private key to approximately nine minutes, which is close to the average time it takes for a bitcoin transaction to be confirmed. The implications of this are significant, with approximately 6.9 million bitcoin being potentially vulnerable to such an attack, especially those where the public key has already been exposed on the blockchain.