How a quantum computer can be used to actually steal your bitcoin in ‘9 minutes’

Quantum computers are not just faster versions of regular computers; they are fundamentally different machines that leverage the unusual rules of physics that only apply at the atomic and subatomic levels. Part 1 of this series delved into the workings of quantum computers, explaining their unique capabilities.

But understanding how quantum computers work is not enough to comprehend how they can be used to steal bitcoin. To achieve this, one must grasp the intricacies of bitcoin’s encryption, its security model, and the specific vulnerabilities that exist. This article delves into bitcoin’s encryption, highlighting the nine-minute window identified by Google’s recent quantum computing paper as the time it takes to break it.

Bitcoin employs elliptic curve cryptography to establish ownership of funds. Each wallet has two keys: a private key, a 256-digit binary number, and a public key derived from the private key using the secp256k1 curve. This process acts as a one-way map, where a private key leads to a unique public key on the curve. The security lies in the fact that while calculating the public key from the private key is straightforward, the reverse process is practically impossible for classical computers.

Shor’s algorithm, developed in 1994, presents a quantum solution to break this one-way trapdoor. By finding the period of a function related to the elliptic curve, Shor’s algorithm efficiently solves the discrete logarithm problem that classical computers struggle with. Quantum computers, with their ability to operate in superposition and entanglement, excel at finding this period and deriving the private key from the public key.

Despite Shor’s algorithm being known for over three decades, the quantum computer required to run it effectively has been elusive. Google’s recent paper reduced the estimated qubit count needed for such an attack, making it more feasible. The team designed quantum circuits that implement Shor’s algorithm against bitcoin’s elliptic curve, demonstrating the potential vulnerability of exposed public keys.

The paper introduced a practical attack scenario where a quantum computer, primed with precomputed data, can swiftly derive private keys once a public key is exposed. This revelation highlights the potential risks posed by quantum computing to bitcoin security, especially for coins with publicly visible public keys.

In conclusion, while quantum computers pose a threat to bitcoin security, the current technology gap limits their immediate impact. However, as hardware advances and vulnerabilities are exploited, the future implications for bitcoin’s security remain a topic of concern. The next article in this series will explore the impact of exposed public keys, recent upgrades like Taproot, and the evolving landscape of quantum computing in the crypto space.