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

This series previously delved into the physics underlying quantum computing, but understanding the technology is only half the battle. To grasp how a quantum computer can be used to steal bitcoin, it's essential to comprehend what it's attacking: the encryption that secures bitcoin transactions. Bitcoin relies on elliptic curve cryptography, a system that uses a pair of keys - a private key and a public key - to prove ownership. The public key is derived from the private key through a complex mathematical operation on a specific curve known as 'secp256k1'. This process is akin to a one-way map, where starting from a known point and taking a certain number of steps leads to a public key, but reversing the process to find the private key is virtually impossible for classical computers. However, a quantum algorithm known as Shor's algorithm can efficiently solve this problem, potentially allowing an attacker to derive a private key from a public key. The recent paper by Google's Quantum AI division has reduced the estimated number of qubits required to run Shor's algorithm against bitcoin's elliptic curve, making the threat more tangible. The attack scenario introduced by Google's paper involves precomputing parts of Shor's algorithm that depend on the elliptic curve's fixed parameters, allowing the quantum computer to sit in a primed state, waiting for a target public key to appear. Once a public key is broadcast, the machine only needs to finish the second half of the calculation, which Google estimates takes around nine minutes. This creates a narrow window for an attacker to derive a private key and submit a competing transaction, potentially redirecting funds. The implications of this are significant, especially for the 6.9 million bitcoin that have already had their public keys exposed on the blockchain, making them vulnerable to an 'at-rest' attack. As quantum computing technology continues to advance, the gap between the theoretical threat and practical reality is closing, posing a significant risk to bitcoin's security.