The Quantum Threat to Bitcoin: How Your Cryptocurrency Could Be Stolen in Under 10 Minutes

The first part of this series delved into the physics behind quantum computing, explaining how it differs from classical computing. However, understanding the mechanics of quantum computing doesn't necessarily reveal how it can be used to steal bitcoin. To grasp this, one must comprehend what quantum computers are attacking and where the weaknesses in bitcoin's security lie. This piece begins by examining bitcoin's encryption system, which utilizes elliptic curve cryptography to verify ownership. Each wallet has a private key, a secret 256-digit binary number, and a public key derived from the private key through a mathematical operation on the 'secp256k1' curve. The process can be thought of as a one-way map, where starting from a known point on the curve and taking a certain number of steps leads to the public key, but reversing this process to find the private key is virtually impossible for classical computers. This one-way function is the backbone of bitcoin's security model, allowing for the creation of digital signatures that prove ownership without revealing the private key. However, the discovery of Shor's algorithm in 1994 introduced a quantum approach that can efficiently solve the discrete logarithm problem, potentially 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, its application has been hindered by the requirement for a large number of stable qubits. Recent estimates by Google have significantly reduced the number of qubits needed, making the threat more tangible. Google's paper also introduced a practical attack scenario, where parts of the calculation 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 bitcoin's average block confirmation time. The implications are alarming, especially for the 6.9 million bitcoin with exposed public keys, which are vulnerable to attack without any time constraint.