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 fundamentally different kind of machine that leverages the unique rules of physics at the atomic and particle level. To understand how a quantum computer can be used to steal bitcoin, it's essential to comprehend what it is attacking and how bitcoin's security is constructed. Bitcoin uses a system called elliptic curve cryptography, which relies on a one-way map to prove ownership. Each wallet has a private key, a secret number, and a public key derived from the private key using a mathematical operation on a specific curve called 'secp256k1'. This one-way map is the foundation of bitcoin's security model, making it virtually impossible for classical computers to reverse the math and determine the private key. However, a quantum algorithm known as Shor's algorithm can break this trapdoor, solving the discrete logarithm problem efficiently. Shor's algorithm utilizes the principles of superposition, entanglement, and interference to find the period of a function, which ultimately reveals the private key. Although Shor's algorithm has been known for over 30 years, its implementation has been hindered by the requirement for a large number of stable qubits to maintain coherence throughout the calculation. Recent research by Google has reduced the estimated number of qubits needed, making the attack more feasible. The study introduced a practical attack scenario, where the parts of Shor's algorithm that depend on the elliptic curve's fixed parameters can be precomputed, allowing the quantum computer to sit in a primed state, waiting for a target public key to appear. Once a public key is visible, the machine only needs to finish the second half of the calculation, which Google estimates takes approximately nine minutes. This timeline is alarming, as it gives the attacker a roughly 41% chance of deriving a private key and submitting a competing transaction 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. 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. The implications of this quantum threat and the ongoing development of quantum computing hardware will be discussed in the next piece of this series.