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

To understand how a quantum computer can be used to steal bitcoin, it's essential to know how bitcoin's security is built and where the weakness lies. Bitcoin uses elliptic curve cryptography, which involves a one-way map that makes it easy to go forward but virtually impossible for classical computers to reverse. However, Shor's algorithm, a quantum algorithm discovered in 1994, can break this one-way trapdoor efficiently. The algorithm uses quantum properties such as superposition, entanglement, and interference to find the period of a function, which ultimately reveals the private key. Google's recent 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 the quantum computer can precompute parts of the algorithm and finish the calculation in about nine minutes once a target public key appears. This creates a window of opportunity for a quantum attacker to derive a private key and submit a competing transaction, with a roughly 41% chance of succeeding before the original transaction confirms. The bigger concern is the 6.9 million bitcoin already exposed on the blockchain, which are vulnerable to an 'at-rest' attack that requires no time constraint.