How Quantum Computing Threatens Bitcoin Security in Under 10 Minutes

To understand how a quantum computer can be used to compromise bitcoin, it's essential to know how bitcoin's security works and where its weaknesses lie. The first part of this series covered the basics of quantum computing, but that's not enough to grasp the threat it poses to bitcoin. This piece delves into the specifics of bitcoin's encryption, why a quantum algorithm can break it, and the implications of Google's recent research. Bitcoin relies on elliptic curve cryptography, which involves a one-way function that makes it easy to generate a public key from a private key but virtually impossible for classical computers to reverse the process. However, a quantum algorithm known as Shor's algorithm can efficiently solve the discrete logarithm problem, thereby breaking the encryption. The algorithm utilizes the principles of superposition, entanglement, and interference to find the period of a function, which is crucial for deriving the private key from the public key. The recent paper by Google has significantly reduced the estimated number of qubits required to run Shor's algorithm against bitcoin's elliptic curve, from millions to fewer than 500,000. This reduction, combined with the possibility of precomputing certain parts of the algorithm, introduces a practical attack scenario where a quantum computer could derive a private key in approximately nine minutes. This timeframe is particularly concerning because it is close to bitcoin's average block confirmation time, giving an attacker a window of opportunity to redirect funds. Furthermore, about 6.9 million bitcoin are already vulnerable to an 'at-rest' attack because their public keys have been exposed on the blockchain. The next part of this series will explore the practical implications of these findings and the potential consequences for bitcoin's security.