Adam Back says 15-bit quantum hack does not threaten Bitcoin

A debate has started in the crypto market after researcher Giancarlo Lelli received a 1 BTC reward from Project Eleven. 

The prize followed his reported success in cracking a 15-bit ECC key using a cloud-based quantum computer.

Project Eleven said Lelli used a modified version of Shor’s algorithm for the test. The group also said its challenge had moved from 6-bit keys to 15-bit keys within seven months, showing faster progress in quantum testing.

Adam Back disputes quantum breakthrough claim

Blockstream CEO Adam Back challenged the idea that the test marked a real quantum attack on crypto. He argued that the result did not prove a useful quantum method against Bitcoin or modern cryptographic systems.

Back said the test looked closer to statistical guessing than a technical breach. In his view, the quantum computer did not solve the kind of hard problem that protects Bitcoin private keys.

Meanwhile, the main criticism focused on the small 15-bit key size. A key of that size has a limited search space, which makes it far easier to test possible answers than real Bitcoin keys.

Former Bitcoin Core developer Jonas Schnelli also questioned the result. He said the researcher checked about 20,000 possibilities out of 32,497, giving the method a high chance of success without quantum advantage.

Schnelli described the result as similar to “flipping a coin.” He also said, “Quantum computing contributed nothing useful here,” arguing that the experiment did not show a real threat to crypto security.

Bitcoin security debate continues

The claim has raised fresh discussion about quantum computing and Bitcoin. Some market watchers see the Project Eleven result as a step toward future risks, while critics say it does not apply to full-strength cryptography.

Back maintained that Bitcoin remains far from the reach of current quantum machines. He said quantum systems would likely target state secrets or banking systems before becoming a practical concern for Bitcoin.

Bitcoin uses far larger key sizes than the one tested in the experiment. For that reason, Back and other skeptics view the challenge as a small-scale test rather than proof that Bitcoin faces an immediate quantum threat.

The episode shows growing interest in post-quantum security across crypto. However, experts remain divided on whether the Project Eleven result marks real progress or only a controlled experiment with limited market relevance.