Security firm Project Eleven has introduced a cryptographic technique designed to allow Bitcoin users to prove wallet ownership even after quantum computers become capable of breaking the network's digital signatures—a moment known as Q-Day.
The announcement, made on Thursday, outlines a recovery mechanism for users who fail to migrate to quantum-safe addresses before such an attack becomes feasible. The core innovation relies on a wallet's key derivation path, enabling the legitimate owner to demonstrate control of the master seed phrase without revealing it. According to Alex Pruden, CEO of Project Eleven, after Q-Day a quantum adversary could derive an elliptic curve private key from a public key, rendering traditional signatures useless as proof of ownership.
“How do you prove you still own a wallet after a quantum computer can forge its signatures?” Pruden wrote on X. “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.”
The work was developed in collaboration with Jim Posen, lead maintainer of the open-source Binius zero-knowledge proof system, and builds on earlier academic research known as “signature lifting,” originally proposed by Alon Sattath and Robert Wyborski. Project Eleven funded Posen’s implementation using Binius to accelerate hash-heavy cryptographic operations. Because a quantum computer cannot reconstruct the parent key from a compromised private key, the technique can differentiate between a real owner and an attacker.
“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,” Pruden explained. “Proving you know that parent key, without revealing it, is something only the real owner can do.”
The recovery mechanism is intended as a fallback for users who miss future migration deadlines. It arrives amid accelerating efforts to prepare Bitcoin for a post-quantum future. In February 2026, Bitcoin developers advanced BIP-360, a quantum-resistant upgrade proposal, into formal review. In March, BTQ Technologies launched a testnet implementation. Then in June, Coinbase’s quantum advisory council warned that roughly 7 million bitcoins could be vulnerable if owners fail to move funds to quantum-safe addresses, and the U.S. government signed executive orders to speed federal post-quantum cryptography transitions.
The prototype is unaudited and would require blockchain protocol support before deployment. Pruden acknowledged the gaps: “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. This gives them a fallback: prove ownership through derivation, not signature, even after that window closes.”
