Quantum Attack Sets New ECC Record With 15-Bit Key Break

• Giancarlo Lelli broke a 15-bit ECC key on public quantum hardware in a record test.
• Project Eleven paid 1 BTC after the result beat the earlier 6-bit break by 512 times.
• Real crypto remains out of reach, but post-quantum migration pressure is rising.

A quantum attack on elliptic curve cryptography has reached a new public milestone. Independent researcher Giancarlo Lelli derived a 15-bit private key using a publicly accessible quantum computer. Project Eleven described it as the largest public break of its kind on quantum hardware so far.

Project Eleven awarded Lelli a 1 BTC bounty through its Q-Day Prize program. The startup launched the challenge last year. It asked participants to break elliptic curve keys ranging from 1 to 25 bits before April 5 this year.

Quantum Break Moves Higher

The company said Lelli recovered the private key from a public key across a search space of 32,767. It added that he used a variant of Shor’s algorithm. That method targets the Elliptic Curve Discrete Logarithm Problem (ECDLP), which supports digital signatures used by Bitcoin, Ethereum, and most blockchains.

Project Eleven said the result remains far below the scale used in real cryptographic systems. Bitcoin uses 256-bit elliptic curve cryptography to secure wallets. That is far more complex than the 15-bit key broken in this test.

In September 2025, engineer Steve Tippeconnic broke a 6-bit elliptic curve key using IBM’s 133-qubit quantum computer. Project Eleven said Lelli’s 15-bit result extends that earlier benchmark by a factor of 512.

The company said the gap between 15 bits and 256 bits is still wide. However, it argued that the distance is increasingly seen as an engineering challenge, not a basic physics limit. 

Quantum Threat Estimates Push Crypto Security Shift

However, a Google Research paper last month estimated that breaking 256-bit elliptic curve cryptography could require fewer than 500,000 physical qubits.

A later paper from the California Institute of Technology and quantum startup Oratomic suggested a lower figure. That report said the requirement could be as low as 10,000 qubits. 

Alex Pruden, chief executive of Project Eleven, said the resources needed for this type of quantum attack keep falling. He also said the barrier to running such an attack in practice is dropping. In his view, that increases the urgency to move toward post-quantum cryptography.

Project Eleven also said that about 6.9 million bitcoins are held in wallets with public keys visible on-chain. It warned that those holdings could face exposure if sufficiently powerful quantum systems are developed.

Some blockchain projects have already started preparing for that possibility. Bitcoin developers have proposed migration paths. Ethereum, Tron, StarkWare, and Ripple have also outlined plans tied to post-quantum cryptography.

Related: Coinbase Raises Alarm Over Quantum Risk to Bitcoin and Crypto Wallets