A quantum computer cracked a 15-bit ECC key — Bitcoin's 256-bit security is still intact, but the timeline is tightening

Researcher Giancarlo Lelli won Project Eleven's Q-Day Prize by using a ~70-qubit quantum computer and a variant of Shor's algorithm to derive a 15-bit elliptic curve private key from its public key — the largest public demonstration of this attack class to date, and a 512x jump over the previous 6-bit benchmark set in September 2025. The prize was one Bitcoin, won by breaking a miniature version of the math that protects Bitcoin.

The gap to a real attack remains enormous. Bitcoin's signature scheme rests on 256-bit elliptic curve cryptography; a 15-bit key represents a search space of 32,767. No publicly known quantum computer can threaten live Bitcoin wallets today. But the surrounding context has shifted: Google cut its ECDLP-256 resource estimates roughly 20-fold in March and set a 2029 post-quantum migration deadline, matched by Cloudflare on April 7. A Caltech/Oratomic preprint —…