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

To understand how a quantum computer can be used to steal bitcoin, it's essential to grasp how bitcoin's security works and where its vulnerabilities lie. Bitcoin utilizes elliptic curve cryptography, which involves a public and private key pair. 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 it's straightforward to generate a public key from a private key but virtually impossible to reverse the process using 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. This algorithm exploits the principles of quantum mechanics, including superposition, entanglement, and interference, to find the period of a function related to the elliptic curve. Once this period is known, the private key can be easily obtained, thereby compromising the security of the bitcoin wallet. The feasibility of this attack has been a topic of interest, with recent research by Google indicating that the number of qubits required to perform such an attack might be significantly lower than previously estimated. This development introduces a new timeline for the potential vulnerability of bitcoin to quantum attacks. The study outlined two quantum circuits that could implement Shor's algorithm against bitcoin's elliptic curve, each requiring fewer than 1,500 logical qubits. A key point of concern is that parts of the calculation can be precomputed, leaving only the final step to be completed once a target public key is identified. Google estimates this final step could take approximately nine minutes, which is perilously close to the average time it takes for a bitcoin transaction to be confirmed. This creates a narrow window of opportunity for a quantum attacker to derive a private key and initiate a transaction that could redirect funds. The most alarming aspect, however, is the vast number of bitcoin (approximately 6.9 million) that are already vulnerable due to their public keys being exposed on the blockchain. These coins are at risk of being stolen without the time pressure of a transaction confirmation race, as an attacker could take as long as needed to compute the private key. The implications of these findings and the potential countermeasures to protect bitcoin against quantum attacks will be discussed in the next part of this series.