A security firm has rolled out a proposed fix for one of Bitcoin’s most worrying post-quantum problems: how to prove you still own a wallet once quantum computers can forge signatures.
Project Eleven on Thursday published a cryptographic approach intended to let legitimate wallet owners prove control of funds even after “Q-Day” — the point at which a quantum computer can break the elliptic-curve cryptography (ECC) that underpins Bitcoin signatures. In a thread on X, CEO Alex Pruden framed the central problem plainly: once a quantum computer can derive a private key from a public key, valid signatures no longer distinguish the real owner from an attacker. “After Q-Day … a valid signature no longer proves ownership. Both the quantum adversary and the legitimate owner are able to produce identical signatures,” Pruden wrote.
How the proposal works
- Instead of relying on a signature tied to a compromised private key, the technique uses a wallet’s key-derivation path. It allows a user to prove control of the parent key (the seed or root key that generates child private keys) without revealing that parent key itself.
- Project Eleven argues that even if a quantum adversary can derive a child private key and forge signatures for an address, they cannot reconstruct the parent key from that child key. Only the true owner — who actually knows the parent seed — can produce the specific proof required.
- The implementation leverages zero-knowledge proof techniques (so the owner proves possession of the parent key without revealing it) and was developed with Jim Posen, lead maintainer of the open-source Binius proof system. Project Eleven funded Posen to implement the approach using Binius, which is optimized for hash-heavy cryptographic workloads.
Origins and context
- The idea builds on a concept known as “signature lifting,” first proposed by researchers Alon Sattath and Robert Wyborski.
- Project Eleven positions the mechanism as a recovery fallback for users who fail to migrate funds to quantum-resistant addresses before Q-Day.
Why this matters now
- The Bitcoin ecosystem is actively preparing for a post-quantum future. In February, BIP-360 entered formal review as a candidate framework for quantum-resistant upgrades. In March, BTQ Technologies launched a working implementation on its Bitcoin Quantum testnet to facilitate development and testing, while drawing attention to the challenge of achieving consensus for any network-wide migration.
- In June, Coinbase’s quantum advisory council warned that roughly 7 million BTC could become exposed if owners don’t move funds to quantum-safe addresses. The same month, U.S. President Donald Trump signed executive orders accelerating the federal government’s adoption of post-quantum cryptography, adding political momentum to the technical work.
- Pruden acknowledged the reality that not every wallet will migrate in time: “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,” he wrote. Project Eleven’s scheme aims to give those users a way to prove ownership “through derivation, not signature,” even after Q-Day.
Bottom line
Project Eleven’s proposal doesn’t stop a quantum-powered thief from deriving a compromised private key and creating valid signatures. Rather, it attempts to re-establish a verifiable distinction between a legitimate owner and an attacker by moving the proof to the wallet’s derivation structure, backed by zero-knowledge techniques. It’s a targeted recovery option that complements broader migration efforts as the industry races to harden Bitcoin against the quantum threat.
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