An Italian researcher, Giancarlo Lelli, has successfully breached a significantly reduced version of a Bitcoin-style cryptographic key using a publicly available quantum computer. This marks the most substantial public demonstration to date of a quantum attack on elliptic curve cryptography.
On Friday, Project Eleven awarded its ‘Q-Day Prize’ of 1 Bitcoin (worth nearly $78,000) to Lelli for decrypting a 15-bit elliptic curve cryptographic key utilizing a variant of Shor’s algorithm. Elliptic curve cryptography secures digital signature systems in Bitcoin, Ethereum, and numerous other blockchains; however, the breached 15-bit key is much smaller than the 256-bit keys protecting real Bitcoin wallets. This breakthrough progresses toward the hypothetical ‘Q-Day’ when quantum computers could threaten hundreds of billions of dollars worth of cryptocurrencies.
“We’re still objectively far from breaking Bitcoin,” stated Alex Pruden, CEO of Project Eleven, in an interview with Decrypt. “But it’s uncertain how long it will take to close that gap and whether we’ll recognize the approach.”
Project Eleven announced today they awarded Lelli the Q-Day Prize for what is considered the most significant quantum attack on elliptic curve cryptography so far. This achievement signifies a 512-fold improvement over previous public demonstrations.
The initiative, launched in 2025 and named after the theoretical date when a sufficiently powerful quantum computer might compromise modern cryptography, aims to assess if publicly accessible quantum systems can overcome criticisms of performing only trivial calculations. Lelli’s work expanded this capability to a 15-bit elliptic curve problem with 32,767 possible solutions.
“This demonstrates that progress is being made in the field,” Pruden commented. “It shows advancements are occurring.”
The successful attack utilized a quantum machine with approximately 70 qubits—capable of existing in multiple states simultaneously, unlike binary bits in traditional computers—and was executed within minutes after development. A panel comprising quantum researchers from academia and industry reviewed the submission, including experts from the University of Wisconsin–Madison and quantum software firm qBraid.
This announcement coincides with major quantum firms and research institutions publishing increasingly aggressive hardware roadmaps and closer estimates for breaching modern cryptography. In March, Google announced a 2029 deadline to transition its systems to post-quantum cryptography due to advancements in quantum hardware, error correction, and reduced timeframes for breaking existing encryption.
Google’s research suggests that less than 500,000 physical qubits might be needed to break Bitcoin, while another study from Caltech and Oratomic estimates the requirement at between 10,000 and 20,000 qubits using a neutral-atom architecture. Pruden predicts ‘Q-Day’ could occur as soon as 2029 in the worst-case scenario, acknowledging that predicting technological breakthroughs is uncertain.
When this breakthrough happens, approximately 6.9 million Bitcoin with publicly visible keys on-chain may become vulnerable to large-scale quantum computers, according to Project Eleven. Nonetheless, some researchers and investors believe the risk is real but years away, suggesting it should be viewed as a long-term engineering challenge rather than an immediate crisis.
Bitcoin developers are evaluating proposals such as BIP-360 for introducing a quantum-resistant transaction format and BIP-361 for phasing out older signature schemes. The Ethereum Foundation has also formed a post-quantum security team, with co-founder Vitalik Buterin outlining steps to replace vulnerable cryptographic elements in Ethereum.
Pruden additionally noted advances in artificial intelligence could accelerate the Q-Day timeline by enhancing quantum error correction or identifying weaker cryptographic targets. “AI can significantly improve the efficiency of quantum computing at scale,” he added. “A key component is error correction.”