A Paris-based quantum computing company has projected that around 30,000 physical qubits could potentially decipher Bitcoin wallet encryption in just over an hour.
The estimated capacity required for a computer to break Bitcoin’s cryptography has significantly decreased.
Researchers from the firm Alice & Bob in Paris have determined that a machine equipped with approximately 30,000 physical qubits could extract a Bitcoin private key from its public counterpart in a little over an hour. They urge Bitcoin developers to initiate the transition to quantum-resistant security measures promptly, as the implementation process could span several years.
Reduction from Millions of Qubits to Thousands
It’s notable how swiftly this estimate has dropped. Earlier assessments suggested that cracking Bitcoin’s cryptography would require millions of physical qubits.
In March 2026, Google Quantum AI revised that number down to fewer than 500,000 physical qubits. Now, Alice & Bob’s latest analysis places it at roughly 30,000, marking a reduction of about 17 times compared to Google’s initially proposed figure.
The primary target is the secp256k1, which is the elliptic-curve cryptography safeguarding Bitcoin wallets. The method of attack involves Shor’s algorithm, a quantum technique capable of reverse-engineering a private key from its public key.
To clarify, physical qubits represent the actual hardware elements and are known for their tendency to be error-prone. In contrast, logical qubits are more stable units created from several physical qubits. Reducing the physical qubit requirement minimizes the most challenging and costly components of the hardware.
Alice & Bob utilizes superconducting “cat qubits” in its hardware design. Their efficiency improvements arise from combining this architecture with a streamlined approach to executing the attack.
Importance of Timeline Over Qubit Count
As of now, no machine of this sort has been constructed. Reliable quantum computers at the necessary scale are still anticipated to be several years away, with researchers forecasting the availability of potentially disruptive hardware by the early 2030s.
Alice & Bob is competitive in this field; founded in 2020, the company has secured around €130 million in funding with ambitions to achieve a 100-logical-qubit fault-tolerant system by 2030.
Google’s 2026 whitepaper provided a more precise insight, predicting that an “on-spend” attack could be executed in 9 to 23 minutes with merely 1,200 to 1,450 logical qubits.
An on-spend attack focuses on active transactions. When a Bitcoin transaction is initiated, the public key becomes identifiable before the transaction finalizes. A sufficiently rapid quantum computer could, theoretically, determine the private key in that brief window and redirect the funds.
The other vulnerable area involves coins that are not in motion. It is estimated that about 6 to 7.1 million BTC, symbolizing nearly 30% of the total supply, are held in wallets with already disclosed public keys.
The Challenge of Bitcoin’s Gradual Upgrades
The researchers emphasize that the crux of their argument revolves around governance rather than mere physics. Bitcoin upgrades are not swift, as the system is structured for stability, not speed.
Any adjustments to the protocol, such as adopting quantum-resistant signatures, would necessitate rigorous testing before they can be put into effect. Alice & Bob warns that this could be a lengthy process. If advanced hardware arrives in the early 2030s and the modifications take years to implement, the timing for action becomes evident.
The researchers also noted that efficiency improvements in hardware could unexpectedly accelerate the timeline. This study itself exemplifies such a shift: the required qubit number has significantly reduced in a single year due to advancements in algorithms and designs, not merely a groundbreaking machine.
Implications for Holders and Developers
The most vulnerable demographic includes holders of coins in wallets with already known public keys. This approximately 30% segment of the total supply is where a capable quantum attacker would focus, and it would be difficult for a protocol upgrade to protect it unless users actively relocate their assets.
For developers, the fundamental challenge lies in coordination. Selecting a quantum-resistant signature scheme, testing its effectiveness, and ensuring widespread adoption across a decentralized network is a long-term endeavor even with unanimous agreement.
Disclosure: This article was reviewed by Estefano Gomez. For further details on our content creation and review processes, please refer to our Editorial Policy.