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

Understanding how a quantum computer works is not enough to comprehend its potential to steal bitcoin. To grasp this, it's essential to delve into bitcoin's encryption, the security it provides, and the weaknesses it poses. This article begins with an analysis of bitcoin's encryption system, which utilizes elliptic curve cryptography to verify ownership. Each wallet contains two keys: a private key, a secret 256-digit binary number, and a public key derived from the private key through a mathematical operation on the secp256k1 curve. The relationship between the two keys can be thought of as a one-way map, where starting from a known point, taking a certain number of steps leads to the public key, but reversing this process is virtually impossible for classical computers. However, in 1994, mathematician Peter Shor discovered a quantum algorithm that can efficiently break this encryption. Shor's algorithm solves the discrete logarithm problem by converting it into a problem of finding the period of a function, which quantum computers can handle efficiently due to their ability to represent multiple values simultaneously and perform operations on them. Google's recent quantum computing 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 parts of the algorithm 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 about nine minutes. This creates a narrow window 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, vulnerable to an 'at-rest' attack that requires no time constraint.