Google’s Quantum AI research division has published a whitepaper warning that the cryptographic foundations of most major cryptocurrencies are more vulnerable to quantum attacks than previously believed.
The findings suggest that the timeline for when quantum computers could pose a real threat to blockchain security may be shorter than previously assumed.
At issue is elliptic curve cryptography (ECC), the mathematical system that secures Bitcoin, Ethereum, and most other blockchains. Quantum computers running Shor’s algorithm can in theory break ECC, but until now the consensus was that doing so would require a very powerful quantum machine.
Google’s new estimates significantly lower the threshold. The company’s researchers have designed quantum circuits capable of breaking the 256-bit elliptic curve discrete logarithm problem (ECDLP-256) used by cryptocurrencies.
Specifically, they achieved this using fewer than 1,200 logical qubits and around 90 million Toffoli gate operations, which roughly represents a 20-fold reduction in the quantum resources previously thought necessary.
The researchers estimate the attack could be executed in minutes on a machine with fewer than 500,000 physical qubits (down from roughly 10 million). This is still beyond today’s hardware, but the findings significantly shorten the timeline for when quantum computers could break current cryptography.
The news comes just days after Google moved up its timeline for transitioning to post-quantum cryptography, setting a 2029 target after faster-than-expected advances in quantum computing.
The tech giant has urged other major industry players, including the cryptocurrency community, to follow suit.
[ Read: Quantum Decryption of RSA Is Much Closer Than Expected ]
Notably, Google chose not to publish the actual quantum circuits behind their newest estimates, instead releasing a zero-knowledge proof: a cryptographic technique that lets independent researchers verify that the claims are mathematically sound without Google having to hand over details that could be used to reproduce the attack.
The approach, developed in coordination with the US government, is being proposed as a model for how the quantum research community should handle sensitive vulnerability disclosures going forward.
Related: Dell and HP Roll Out Quantum-Resistant Device Security
Related: Cyber Insights 2026: Quantum Computing and the Potential Synergy With Advanced AI
Related: Google Working Towards Quantum-Safe Chrome HTTPS Certificates
