Researcher breaks 15-bit elliptic curve key in ‘largest quantum attack,’ wins 1 bitcoin bounty from Project Eleven

Independent researcher Giancarlo Lelli derived a 15-bit elliptic curve key using a publicly accessible quantum computer, in what Project Eleven called the “largest quantum attack” on elliptic curve cryptography to date, albeit at a scale far below that used in real-world cryptographic systems.

Project Eleven, a post-quantum security startup, awarded a 1 BTC bounty, currently worth over $78,000, to Lelli as part of its “Q-Day Prize.” The bounty program was launched last year by the project to break elliptic-curve keys ranging from 1 to 25 bits before April 5 this year.

Before Lelli, an engineer named Steve Tippeconnic broke a 6-bit elliptic curve key in September 2025 using IBM’s 133-qubit quantum computer. That demonstration was the first public break of this type on quantum hardware, Project Eleven said, noting that Lelli’s 15-bit result extends it by a factor of 512.

“Lelli derived a private key from its public key across a search space of 32,767 using a variant of Shor’s algorithm,” Project Eleven said. “Shor’s targets the Elliptic Curve Discrete Logarithm Problem (ECDLP), the math underlying the digital signature schemes securing Bitcoin, Ethereum, and most blockchains.”

Bitcoin uses 256-bit elliptic curve cryptography to secure wallets, which is far larger than the 15-bit key broken in this demonstration.

“The distance from 15 bits to 256 bits is large, but the gap is increasingly viewed as an engineering problem and not a fundamental physics problem,” the project said, though experts remain divided on how quickly such systems could scale to real-world cryptographic levels.

Quantum risks for crypto

Discussions about quantum risks for crypto have grown in recent months. A Google Research paper last month estimated that breaking 256-bit elliptic curve cryptography could require fewer than 500,000 physical qubits. A subsequent paper from the California Institute of Technology and quantum startup Oratomic suggested that the number could be as low as 10,000 qubits. Current quantum systems remain far below these thresholds.

“The resource requirements for this type of attack keep dropping, and the barrier to running it in practice is dropping with them,” said Alex Pruden, CEO of Project Eleven. He added that Lelli’s demonstration highlights the urgency to migrate to post-quantum cryptography sooner rather than later.

Project Eleven said roughly 6.9 million bitcoin are held in wallets where public keys are visible onchain, exposing them to quantum attacks if sufficiently powerful systems are developed.

Blockchain projects have started to prepare for such risks. Bitcoin developers have proposed migration paths, while other networks and companies, including Ethereum, Tron, StarkWare, and Ripple, have outlined plans related to post-quantum cryptography.

At the same time, some analysts have cautioned against overreacting. Research firm Bernstein recently said quantum computing should be seen as a medium to long-term upgrade cycle rather than an immediate risk.

Project Eleven is backed by investors including Castle Island Ventures, Coinbase Ventures, and Variant. Earlier this year, the company raised $20 million in a Series A round at a $120 million post-money valuation to support its work on post-quantum security.

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