Quantum computers may break bitcoin’s core cryptography with 20 times fewer resources than previously estimated. The revised threshold compresses the industry’s timeline to transition toward quantum-resistant security models.
Google Research said new circuit designs could solve the elliptic curve discrete logarithm problem (ECDLP-256), which underpins bitcoin, using fewer than 500,000 physical qubits. The models rely on 1,200 to 1,450 logical qubits and up to 90 million Toffoli gates, with execution times measured in minutes. That speed introduces the possibility of real-time attacks within bitcoin’s 10-minute block window.
Can Quantum Computers Attack Bitcoin Transactions In Real Time?
The updated estimates suggest attackers could target transactions while they are still pending in the mempool. These so-called “on-spend” attacks differ from earlier concerns focused on dormant wallets, expanding the threat surface to active network usage. But the timeline remains measured in years, not months, according to Google’s assessment.
Still, the margin for mitigation is narrowing. Google now targets 2029 for a full transition to post-quantum cryptography (PQC), aligning with broader industry efforts. By comparison, many blockchain systems have yet to finalize upgrade paths for quantum resistance, leaving coordination risks across decentralized ecosystems.
“This is not merely a distant danger to dormant keys,” Google’s research team wrote, warning that faster quantum systems could compromise transactions before confirmation.
The firm urged blockchain networks to accelerate migration efforts without delay.
Yet quantum risk is already influencing capital allocation decisions. Christopher Wood, global head of equity strategy at Jefferies, removed a 10% bitcoin allocation from a model portfolio earlier this year, citing long-term cryptographic uncertainty. Will institutional investors reassess exposure as quantum timelines tighten?
The next catalyst will center on concrete implementation plans for PQC across major networks, including whether bitcoin developers converge on a standardized upgrade path before quantum hardware reaches critical thresholds.
