Expert Analysis on Quantum Computing's Impact on Bitcoin
While the shadow of the quantum computer looms over digital security, opinions diverge on whether Bitcoin could truly waver. Faced with the hypothesis of a network made vulnerable by machines capable of breaking SHA-256, some anticipate an imminent threat, while others temper their expectations. Among them, Adam Back, a prominent figure in the cypherpunk movement and CEO of Blockstream, advocates for a nuanced understanding. His technical and strategic insights reposition the debate on concrete grounds, moving away from catastrophic scenarios and posing crucial questions about the future resilience of the protocol.
Adam Back Reassures: Bitcoin Faces No Direct Risk for Several Decades
While the quantum threat approaches incrementally, Adam Back provided a direct response on November 15 regarding Bitcoin's potential vulnerability to quantum computing: "probably not before 20 to 40 years."
For the CEO of Blockstream, who is cited in Satoshi Nakamoto's whitepaper, fears of a cryptographic collapse are, at this stage, largely premature. He specified that NIST-validated post-quantum cryptography algorithms already exist and could be integrated "well before quantum computers capable of breaking cryptographic systems arrive."
These statements challenge a video by Chamath Palihapitiya that claimed Bitcoin could be compromised within two to five years. Adam Back rejects this prediction, basing his assessment on the current state of quantum hardware, which is still far from reaching the critical threshold required for such an attack.
To illustrate the significant gap between current quantum computer capabilities and the technical requirements to threaten Bitcoin, several concrete elements are highlighted:
- •Breaking SHA-256, the cryptographic foundation of Bitcoin's security, would necessitate approximately 8,000 logical qubits. It is important to note that these are not simple physical qubits but extremely stable and error-corrected qubits.
- •The current record is held by Caltech with 6,100 physical qubits, which is far from sufficient to conduct a viable attack. This machine cannot even break RSA-2048, a task that theoretically requires about 4,000 logical qubits in a perfect model.
- •Error correction represents a major obstacle; for instance, Quantinuum has achieved 98 physical qubits, but this has only enabled the production of 48 truly usable logical qubits.
- •On the side of universal quantum gate systems, Atom Computing has surpassed the 1,000 physical qubit mark, yet it has not approached a capacity exploitable for large-scale cryptanalysis.
In essence, the technological gap remains vast. According to Adam Back, Bitcoin has ample time to adapt and possesses the necessary cryptographic tools to anticipate these developments without undue haste.
An Indirect Vulnerability: The "Harvest Now, Decrypt Later" Threat
While the direct threat of a quantum attack on Bitcoin appears largely premature today, some researchers emphasize a different, more insidious danger: the storage of encrypted data with the intent to decrypt it later. This strategy is known as "harvest now, decrypt later."
Gianluca Di Bella, a specialist in smart contracts and zero-knowledge proofs, believes this threat should prompt immediate action, stating, "we should migrate now." He suggests that even if commercial quantum computers are still ten to fifteen years away, "large institutions like Microsoft or Google could have a solution within a few years," indicating that the race for quantum supremacy might accelerate faster than anticipated.
This attack strategy, while not directly operative on Bitcoin's model where security relies on the possession of private keys rather than data confidentiality, concerns a much broader range of encrypted communications. It could have dramatic consequences in sensitive political or geopolitical contexts. For example, a dissident protected today by asymmetric encryption could see their data compromised in a decade if it was intercepted today by an entity that later acquires a quantum computer capable of reading it.
This raises questions about technological governance and digital sovereignty. If post-quantum standards are already validated, when and how will they be integrated into existing protocols? Who will oversee the implementation? And, crucially, will Bitcoin users be prepared to consent to the potential technical changes required? As giants in cloud computing, AI, and Web3 invest heavily in quantum technology, the question of post-quantum migration emerges as a long-term imperative, though its precise timing remains uncertain.