The Quantum Threat to Bitcoin: How Your Cryptocurrency Could Be Stolen in Under 10 Minutes

Understanding quantum computers is one thing, but grasping how they can be utilized to steal bitcoin requires knowledge of what they are attacking and where the vulnerabilities lie. This piece begins by explaining bitcoin's encryption, leading up to the discovery of how a quantum algorithm can break it in approximately nine minutes, as indicated by Google's recent quantum computing research. Bitcoin employs elliptic curve cryptography, a system that involves two keys: a private key, which is a secret number, and a public key derived from the private key through a mathematical operation. The process can be thought of as a one-way map, where starting from a known point, taking a series of steps defined by the curve's mathematics leads to a public key. While moving forward in this map is straightforward, reversing the process is virtually impossible for classical computers due to the elliptic curve discrete logarithm problem. However, a quantum algorithm known as Shor's algorithm can efficiently solve this problem, thereby breaking the encryption. Shor's algorithm works by converting the problem into finding the period of a function, which quantum computers can solve efficiently due to their ability to represent multiple values simultaneously and perform operations on them all at once. The recent paper by Google's Quantum AI division, in collaboration with other researchers, has significantly reduced the estimated number of qubits required to run Shor's algorithm against bitcoin's encryption, from millions to fewer than 500,000. This reduction, along with the introduction of a practical attack scenario, changes the perspective on the quantum threat to bitcoin. The scenario involves precomputing parts of the algorithm that depend on the elliptic curve's fixed parameters, allowing the quantum computer to sit in a primed state, ready to finish the calculation once a target public key appears. Google estimates this could be done in about nine minutes, which is close to bitcoin's average block confirmation time. This creates a narrow window for a quantum attacker to derive a private key and submit a competing transaction. The bigger concern, however, is the large number of bitcoins already exposed and vulnerable to attack. The implications of this vulnerability and the ongoing advancements in quantum computing hardware will be explored further.