A quantum computer enabled a researcher to steal a 15-bit crypto key and earn one bitcoin

Brief about the event

Independent researcher Giancarlo Lelli cracked a 15‑bit elliptic curve key on a publicly available quantum service and received the Q‑Day Prize from the startup Project Eleven – one bitcoin worth about $78 000. This achievement exceeded the previous public record by 512 times and became the largest demonstration of a practical quantum attack on the cryptography that protects Bitcoin and other blockchains.

How it was done
1. Converting the public key to the private key

Lelli used Shor’s algorithm (1994) – instead of brute‑forcing all possibilities he directly computed the private key from the public one. For a 15‑bit key there are only 32 767 possible combinations.

2. Platform

The attack was carried out on cloud quantum hardware that is publicly accessible, not in a national laboratory or on a proprietary chip.

3. Result

Breaching the key cost 1 BTC (~$78 000) and became the largest public example of Bitcoin cryptography being broken.

What this means for the crypto world
- Crypto wallets at risk – those whose public keys are already visible on the blockchain. According to Project Eleven, about 6.9 million BTC (≈ 1/3 of total supply) reside at such addresses, including the immutable 1 million BTC held by Satoshi Nakamoto.

- Lowering quantum resource requirements – Google Research last month showed that cracking a 256‑bit key will need fewer than 500,000 physical qubits, whereas earlier estimates were in the millions. This means the practical barrier is gradually falling.

- Plans to transition to post‑quantum cryptography

* Bitcoin: BIP‑360 (address types with quantum protection).
* Ethereum, Tron, StarkWare and Ripple have already published migration strategies.

Comparison with the previous record
- Steve Tippenko – in September 2025 he cracked a 6‑bit key on IBM’s 133‑qubit quantum computer.
- Lelli surpassed that result by 512 times over seven months using publicly available cloud hardware.

Conclusion
It has been proven that modern quantum services can perform practical attacks on Bitcoin cryptography. This accelerates the need to move to post‑quantum protocols and highlights the vulnerability of large wallets with public keys on the blockchain.