The Quantum Threat to Bitcoin: How Your Coins Can Be Stolen in Under 10 Minutes

To comprehend how a quantum computer can be utilized to steal bitcoin, it is essential to understand the target: the encryption that secures bitcoin transactions. The security model of bitcoin relies on elliptic curve cryptography, a system that utilizes a pair of keys - a private key and a public key. The private key, a secret number, is used to create a digital signature, a mathematical proof that confirms ownership of the coins. The public key, derived from the private key, is shared publicly without compromising the security of the private key. However, the emergence of quantum computers and the development of Shor's algorithm have introduced a significant threat to this security model. Shor's algorithm can efficiently solve the discrete logarithm problem, allowing a quantum computer to derive the private key from the public key. Recent estimates suggest that a quantum computer with fewer than 500,000 qubits could potentially break bitcoin's encryption. Google's Quantum AI division has designed quantum circuits that implement Shor's algorithm, reducing the required number of qubits. The introduction of a practical attack scenario has significant implications for the security of bitcoin transactions. If a quantum computer can precompute the parts of Shor's algorithm that depend on the elliptic curve's fixed parameters, it can sit in a primed state, waiting for a target public key to appear. Once the public key is visible, the quantum computer can derive the private key in approximately nine minutes, allowing it to submit a competing transaction and potentially steal the coins. This mempool attack is alarming, but it requires a quantum computer that does not yet exist. A more pressing concern is the 6.9 million bitcoin that are already vulnerable to an 'at-rest' attack, as their public keys have been permanently exposed on the blockchain. The development of quantum computers and their potential to break bitcoin's encryption poses a significant threat to the security of bitcoin transactions.