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

Quantum computers are not just faster versions of regular computers, but a different kind of machine that uses the principles of quantum mechanics to perform calculations. The first part of this series explored the physics of quantum computing, but understanding how it works is not enough to comprehend how it can be used to steal Bitcoin. To do that, we need to delve into the security mechanisms of Bitcoin and identify the weaknesses that a quantum computer can exploit. Bitcoin uses a system called elliptic curve cryptography to verify ownership of coins. Each wallet has a private key, which is a secret number, and a public key, which is derived from the private key using a mathematical operation. The public key is like a one-way map, where it's easy to calculate the public key from the private key, but virtually impossible to do the reverse. This is known as the elliptic curve discrete logarithm problem. However, a quantum algorithm called Shor's algorithm can solve this problem efficiently, allowing a quantum computer to break the encryption and steal the coins. The algorithm uses the principles of superposition, entanglement, and interference to find the period of a function, which is essential to breaking the encryption. Google's recent research has reduced the estimated number of qubits required to run Shor's algorithm against Bitcoin's encryption from millions to fewer than 500,000. The study also introduced a practical attack scenario, where a quantum computer can precompute parts of the algorithm and then finish the calculation in about nine minutes once a target public key appears. This means that if a user broadcasts a transaction and their public key is visible, a quantum attacker has roughly nine minutes to derive the private key and submit a competing transaction. The math gives the attacker a roughly 41% chance of succeeding. However, the bigger concern is the 6.9 million Bitcoin sitting in wallets where the public key has already been exposed, making them vulnerable to an 'at-rest' attack. A quantum computer running Shor's algorithm can turn a Bitcoin public key into the private key that controls the coins, allowing the attacker to steal the funds.