Bitcoin Q-Day Recovery Proposal Aims to Let Users Prove Ownership After Quantum Attack

As concerns about Bitcoin’s quantum security continue to grow, security firm Project Eleven unveiled a cryptography on Thursday technology designed to address a major problem by allowing users to prove ownership of a wallet after quantum computers become capable of deriving private keys and generating valid digital signatures.

In one wire On Wednesday, Project Eleven CEO Alex Pruden said the central challenge is not protecting wallets from quantum attacks, but proving ownership once those attacks become possible.

“How do you prove you still own a wallet after a quantum computer can forge its signatures?” Pruden wrote. “After Q-Day, once a quantum computer can derive an ECC private key from its public key, a valid signature no longer proves ownership. Both the quantum adversary and the legitimate owner can produce identical signatures.”

“Q-Day” refers to the moment when a quantum computer can break the elliptic curve cryptography that secures Bitcoin transactions. The concern in the industry is that an attacker could use a quantum computer to derive a private key from a public key, making digital signatures unreliable as proof of wallet ownership.

What that means in practice is that an attacker can target vulnerable wallets, forge their digital signature, and move Bitcoin without the owner’s permission.

Project Eleven’s technique leverages a wallet’s key derivation path, allowing users to prove they have control over the parent key used to generate a wallet’s private key without revealing it.

Because a quantum computer can’t reconstruct that parent key, the company says it can distinguish a legitimate owner from an attacker even after a wallet’s private key has been compromised.

“So even after Q-Day, an attacker who has cracked your address’s private key cannot understand or compute the core phrase from which it is derived. Proving that you know that parent key, without revealing it, is something only the real owner can do,” Pruden wrote.

According to Pruden, the work was developed in collaboration with Jim Posen, lead maintainer of the open-source Binius zero-knowledge proof system, and builds on a technique known as “signature lifting,” first proposed by researchers Alon Sattath and Robert Wyborski. Project Eleven funded Posen to implement the approach using Binius, an open-source proof system designed to accelerate hash-heavy cryptographic operations.

The proposed recovery mechanism is aimed at users who miss a future migration to quantum-safe addresses and comes as efforts to prepare Bitcoin for a post-quantum future accelerate.

In February, Bitcoin developers brought BIP-360, a Bitcoin improvement proposal, to the formal review process, laying the groundwork for future quantum-resistant upgrades. In March, BTQ Technologies released the first working implementation on its Bitcoin Quantum testnet, allowing developers to test the proposal while highlighting the challenge of building consensus for a network-wide upgrade.

In June, Coinbase’s quantum advisory board urged blockchain developers to start planning post-quantum migrations, warning that around 7 million Bitcoin could ultimately be vulnerable to quantum attacks if owners fail to move funds to quantum-safe addresses. Later that month, President Donald Trump signed executive orders speeding the federal government’s transition to post-quantum cryptography, boosting broader efforts to prepare for Q-Day.

“As much as I would like the entire world to take a quantum migration plan seriously, the reality is that some digital asset wallets will miss the window,” Pruden wrote. “This gives them a fallback: prove ownership by inference, not by signature, even after that window closes.”