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

Understanding quantum computers is not enough to comprehend how they can be used to steal bitcoin. To grasp this, it's essential to know how bitcoin's security works and where its weaknesses lie. This piece delves into bitcoin's encryption, explaining how it uses elliptic curve cryptography to verify ownership. Every wallet has a private key, a secret 256-digit binary number, and a public key derived from it using a mathematical operation on the secp256k1 curve. The process is akin to a one-way map, where it's easy to calculate the public key from the private key but virtually impossible for classical computers to do the reverse. This one-way function is the foundation of bitcoin's security model. However, a quantum algorithm known as Shor's algorithm can break this security by solving the elliptic curve discrete logarithm problem efficiently. Shor's algorithm works by finding the period of a function related to the elliptic curve, which is a task that quantum computers are particularly suited for due to their ability to exist in a superposition, apply functions to all possible inputs simultaneously, and use quantum operations like the Fourier transform to find the correct period. Once the period is found, the private key can be easily recovered, compromising the security of the bitcoin wallet. The reason bitcoin remains secure today is that running Shor's algorithm requires a quantum computer with a large number of stable qubits. Recent estimates by Google have significantly reduced the number of qubits needed, from millions to fewer than 500,000, making the threat more tangible. Google's paper also introduced a practical attack scenario where parts of Shor's algorithm can be precomputed, leaving only the final step to be completed once a target public key is identified. This final step can take approximately nine minutes, which is close to the average block confirmation time of bitcoin, giving an attacker a window of opportunity to derive a private key and submit a competing transaction. The bigger concern is the large number of bitcoin wallets with public keys already exposed on the blockchain, making them vulnerable to attack without any time constraint.