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

The first part of this series delved into the physics behind quantum computing, but understanding how it works is only half the story. To grasp the threat it poses to bitcoin, we need to examine the target: the encryption that secures the cryptocurrency. This piece will break down how bitcoin's security works, why a quantum algorithm can break it, and the implications of Google's recent research on the timeline. Bitcoin relies on a system called elliptic curve cryptography to verify ownership. Each wallet has a pair of keys: a private key, which is a secret number, and a public key derived from the private key through a complex mathematical operation. The relationship between the two keys is akin to a one-way map, where it's easy to generate the public key from the 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 the private key from the public key and steal the associated bitcoin. The algorithm leverages the principles of quantum mechanics, including superposition, entanglement, and interference, to find the period of a function related to the elliptic curve. This process, which would take an impractically long time for a classical computer, can be completed relatively quickly by a quantum computer. The security of bitcoin currently relies on the fact that building a quantum computer capable of running Shor's algorithm is beyond our technical capabilities. However, recent research by Google has reduced the estimated number of qubits required for such a computation, bringing the threat closer to reality. The study introduced a practical attack scenario where parts of the algorithm can be precomputed, leaving only the final steps to be completed once a target public key is identified. This could potentially allow an attacker to derive a private key and submit a competing transaction within the timeframe of a standard block confirmation. While the immediate threat is still theoretical, requiring a quantum computer that does not yet exist, the long-term implications are significant, particularly for the approximately 6.9 million bitcoin whose public keys have already been exposed on the blockchain.