Concerns about quantum computer attacks on Bitcoin, long viewed as a distant threat, are becoming increasingly real. Project Eleven, a company focused on quantum security, has awarded the so-called Q-Day prize—worth 1 BTC—to independent researcher Giancarlo Lelli. Lelli succeeded in breaking the encryption of a 15-bit elliptic curve key using public quantum hardware and managed to derive the private key from the public key.
Rapid developments in quantum attacks
Valued at roughly $78,000, this award marks the largest publicly documented quantum attack demonstration to date. The attack method used poses a potential future threat not just to Bitcoin, but to other major blockchain networks such as Ethereum (ETH). Crypto wallets rely on elliptic curve cryptography to verify ownership of funds—while public keys are visible to everyone, the underlying private keys are presumed unbreakable under current conditions.
However, the quantum technique called Shor’s algorithm, first described in 1994, fundamentally challenges this assumption. Despite Lelli’s achievement, Bitcoin is not expected to be breached imminently, as its security depends on far more complex 256-bit elliptic curve keys, compared to the 15-bit key cracked in this experiment—a drastic difference, with Bitcoin’s unrestricted keys exceeding the smaller keyspace by trillions of times.
Breakthroughs in hardware and research
Until seven months ago, the largest known public quantum cracking feat involved IBM’s 133-qubit quantum computer breaking a 6-bit key. Lelli’s demonstration increases that complexity by 512-fold. In this context, “bit” refers to the basic unit in classical computing, while “qubit” is its quantum counterpart, exponentially expanding computational possibilities.
The theoretical progression in this field is also accelerating. Last month, Google Research published a study reducing the estimated number of physical qubits needed for a full 256-bit attack to below 500,000—down from previous projections that cited several millions.
Alex Pruden, CEO of Project Eleven, pointed out that the resources needed for this kind of attack are dropping quickly, effectively lowering the practical threshold for a real-world breach.
Mounting concerns and countermeasures in the Bitcoin community
Pruden further underlined that the winning submission did not originate from a state lab or with proprietary quantum chips, but from an independent researcher utilizing cloud-accessible quantum hardware. Currently, an estimated 6.9 million Bitcoin—about a third of all BTC, including 1 million believed to belong to Satoshi Nakamoto—are held in wallets whose public keys are visible on the blockchain.
If a quantum computer capable of breaking 256-bit elliptic curve cryptography ever materializes, these wallets could face significant risk. To counter this, Bitcoin developers have introduced quantum-resistant address formats such as BIP-360. Other blockchains, including Ethereum, Tron, StarkWare, and Ripple, have also released their own quantum migration strategies.
“A 15-bit key is still far too small for real-world systems, yet the evolution has sparked notable activity among developer communities and the broader blockchain ecosystem,” industry analysts observe.
In summary, cracking a 15-bit key does not directly endanger Bitcoin, but it signals rapid progress in real-world quantum attack attempts and increasingly narrow theoretical limits. These developments underscore the growing need for quantum-secure measures in blockchain-based assets.
