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

Understanding the principles of quantum computing is crucial, but knowing how it can be utilized to steal bitcoin requires insight into the target - the security of bitcoin and where its weaknesses lie. This piece begins with an explanation of bitcoin's encryption system, which relies on elliptic curve cryptography to verify ownership. Every bitcoin wallet has two keys: a private key, kept secret, 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, taking a certain number of steps defined by the curve's math leads to a public key. While going forward is straightforward, reversing the process to find the private key from the public key is virtually impossible for classical computers due to the elliptic curve discrete logarithm problem. However, in 1994, mathematician Peter Shor discovered a quantum algorithm that can efficiently solve this problem, potentially breaking bitcoin's security. Shor's algorithm works by converting the problem into finding the period of a function, which quantum computers can solve using superposition, entanglement, and interference. Despite the algorithm being known for over 30 years, its implementation has been hindered by the need for a large number of stable qubits. Recent research by Google, in collaboration with the Ethereum Foundation and Stanford, has significantly reduced the estimated number of qubits required, from millions to fewer than 500,000. This reduction, along with the introduction of a practical attack scenario, changes the perspective on the quantum threat to bitcoin. The scenario involves precomputing parts of Shor's algorithm that depend on the elliptic curve's fixed parameters, allowing a quantum computer to sit in a primed state, ready to derive a private key once a target public key appears. Google estimates this process could take approximately nine minutes, which is close to bitcoin's average block confirmation time. This creates a narrow window for a quantum attacker to derive a private key and submit a competing transaction. The most alarming aspect, however, is the vulnerability of the 6.9 million bitcoin that have had their public keys exposed on the blockchain, which could be targeted without any time constraint.