The notion that quantum computers pose an imminent threat to bitcoin's security has been a topic of discussion in recent times. However, research suggests that the energy required to launch such an attack is substantial, equivalent to the energy output of a star. Two recent papers have shed light on this issue, with one paper demonstrating the physical impossibility of a quantum computer outperforming traditional miners due to the enormous energy requirements, and another paper highlighting the ease of replicating supposed quantum factoring breakthroughs using a 1981 home computer and a simple algorithm. The security of bitcoin rests on two types of mathematics, and quantum computers pose a threat to these in two different ways.
The first, known as Shor's algorithm, targets wallet security, while the second, known as Grover's algorithm, applies to mining. However, the advantages of Grover's algorithm are largely negated when considering the physical constraints of building such a machine.
The first paper, published in March 2026, examines the feasibility of a quantum computer outperforming traditional miners using Grover's algorithm. The researchers conclude that running Grover's algorithm against the SHA-256 math formula used in bitcoin mining would be physically impossible due to the enormous energy requirements.
The estimated energy needed to power such a quantum mining fleet would be roughly 10²³ qubits drawing 10²⁵ watts, approaching the energy output of a star. In contrast, the current bitcoin blockchain draws approximately 15 gigawatts. The second paper, from researchers at the University of Auckland and Zürcher Hochschule, aims to replicate every major quantum factoring breakthrough of the past two decades.
The authors successfully replicate these breakthroughs using a 1981 VIC-20 home computer, an abacus, and a dog trained to bark three times. The researchers argue that many of the supposed quantum factoring breakthroughs are the result of rigged numbers or classical preprocessing, which allows researchers to claim impressive-sounding results without actually advancing the underlying science.
The authors propose new evaluation standards that would require random numbers, no preprocessing, and factors kept secret from the experimenters. The takeaway from these papers is not that quantum computing poses no threat to bitcoin, but rather that the threat is often exaggerated. The real vulnerability lies in bitcoin wallets, particularly older or reused addresses where key information is already exposed on the blockchain.
Recent research suggests that the computing power needed for a quantum attack on bitcoin wallets could decrease sharply, but building such a machine is currently physically impossible. Developers are working on fixes, including ways to reduce key exposure and new types of signatures designed to withstand quantum attacks.
While the quantum threat to bitcoin is real, it is essential to remember that building the machines used to attack the blockchain is constrained by the limits of physics.