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

The first part of this series explored the fundamental principles of quantum computing. However, understanding how quantum computers work is only half the story. To grasp how they can be used to steal bitcoin, it's essential to comprehend what they are attacking - the security framework of bitcoin itself. This piece begins with an examination of bitcoin's encryption system, known as elliptic curve cryptography, and progresses to explain how a quantum algorithm can break it, focusing on the 'nine-minute window' identified by Google's recent quantum computing paper. Bitcoin's security is built on a one-way function, where a private key is used to generate a public key, but classical computers cannot reverse this process. However, a quantum algorithm known as Shor's algorithm can efficiently break this one-way function, potentially allowing an attacker to derive a private key from a public key. The algorithm works by converting the problem into finding the period of a function, which quantum computers can solve efficiently using superposition, entanglement, and interference. Despite Shor's algorithm being known for over 30 years, the lack of a sufficiently powerful quantum computer has prevented its use. Recent research by Google has reduced the estimated number of qubits required to run Shor's algorithm against bitcoin's encryption, from millions to fewer than 500,000, making the threat more tangible. The study introduced a practical attack scenario where parts of the algorithm can be precomputed, waiting for a target public key to appear. Once a public key is visible, the quantum computer only needs about nine minutes to derive the private key, which is alarming given bitcoin's average block confirmation time of 10 minutes. This creates a 'mempool attack' scenario where an attacker has a roughly 41% chance of redirecting funds before the original transaction confirms. Moreover, approximately 6.9 million bitcoin are vulnerable to an 'at-rest' attack, as their public keys have been permanently exposed on the blockchain. The implications of this vulnerability and the race to develop quantum-resistant cryptography will be explored in the next piece.