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

The first part of this series delved into the physics behind quantum computing, but understanding how it works is only half the story. To grasp the threat it poses to Bitcoin, we need to explore the target: the encryption that secures the cryptocurrency. Bitcoin relies on elliptic curve cryptography, which uses a one-way function to derive a public key from a private key. This function is virtually impossible for classical computers to reverse, but a quantum algorithm known as Shor's algorithm can break it. Shor's algorithm exploits the properties of quantum mechanics to solve the discrete logarithm problem, which is the foundation of Bitcoin's security. The algorithm uses superposition, entanglement, and interference to find the period of a function, which ultimately reveals the private key. Google's recent research paper reduced the estimated number of qubits required to run Shor's algorithm against Bitcoin's elliptic curve from millions to fewer than 500,000. The paper also introduced a practical attack scenario, where a quantum computer can precompute parts of the algorithm and then finish the calculation in approximately nine minutes once a target public key appears. This timeline is concerning, as it gives an attacker a roughly 41% chance of deriving a private key and submitting a competing transaction before the original transaction confirms. The bigger concern, however, is the 6.9 million bitcoin that are already vulnerable to an 'at-rest' attack, as their public keys have been permanently exposed on the blockchain. A quantum computer running Shor's algorithm can turn these public keys into private keys, giving the attacker control over the coins.