Proving Ownership After Q-Day: Project Eleven Proposes Quantum-Resistant Recovery for Lost Bitcoin Wallets

As the digital asset industry prepares for the theoretical arrival of quantum computing, the race to secure decentralized networks is heating up. On Thursday, security firm Project Eleven unveiled a novel cryptographic technique designed to address one of the most complex challenges of this transition: verifying wallet ownership after “Q-Day”—the hypothetical moment when quantum computers become powerful enough to break the elliptic curve cryptography that secures the Bitcoin network.

In a detailed thread on X on Wednesday, Project Eleven CEO Alex Pruden argued that the primary threat to the network isn’t just shielding active wallets from quantum attacks, but rather establishing a secure way to prove who actually owns them once legacy cryptographic defenses fail.

“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 are able to produce identical signatures.”

Under Bitcoin’s current cryptographic framework, transactions are validated using digital signatures. However, if an attacker can utilize a quantum computer to reverse-engineer a private key from its corresponding public key, they can easily forge valid digital signatures. In practice, this means an attacker could target vulnerable wallets, forge their digital signature and move Bitcoin without the owner’s permission.

To solve this, Project Eleven’s technique leverages the mathematical relationship inherent in modern hierarchical deterministic (HD) wallets. Instead of relying on a standard digital signature, the method uses a wallet’s key derivation path. This allows users to prove they control the parent key (the master seed phrase) used to generate a wallet’s private key without revealing it to the public.

Because a quantum computer cannot reconstruct that parent key from a child private 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’s broken your address’s private key does not hold, and can’t compute, the seed phrase it was derived from. Proving you know that parent key, without revealing it, is something only the real owner can do,” Pruden wrote.

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

While the development represents a significant step forward in post-quantum recovery research, the prototype remains unaudited. Furthermore, implementing such a mechanism on the live Bitcoin network would require protocol-level support, meaning the community would need to agree on a soft or hard fork to integrate the verification logic into the blockchain.

The proposal arrives amid a broader, accelerating push within the crypto ecosystem to prepare for the quantum threat. In February, Bitcoin developers advanced BIP-360, a Bitcoin improvement proposal, into the formal review process, laying the groundwork for future quantum-resistant upgrades. Shortly after, 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.

The urgency of these preparations was underscored in June when Coinbase’s quantum advisory council urged blockchain developers to begin planning post-quantum migrations, warning that roughly 7 million Bitcoin could eventually be vulnerable to quantum attacks if owners fail to move funds to quantum-safe addresses. The geopolitical dimension of this cryptographic race also became clearer later that month, when President Donald Trump signed executive orders speeding the federal government’s transition to post-quantum cryptography, adding momentum to broader efforts to prepare for Q-Day.

Project Eleven’s proposed recovery mechanism is specifically intended as a safety net for users who miss a future migration to quantum-safe addresses.

“As much as I’d love for 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 through derivation, not signature, even after that window closes.”