Bitcoin's developer community should stop waiting for certainty around quantum computing timelines and focus on deploying a post-quantum signature scheme, Project Eleven CEO Alex Pruden told CoinDesk at Consensus Miami on Wednesday. Pruden said the asymmetry between acting now and waiting favors action.
"We added some new cryptography, we sort of baked in this optionality, turns out we didn't need it yet, but at least we have it," he said, describing the worst-case scenario of early action. The worst case of delay is far graver: a sufficiently powerful quantum computer could derive private keys from any exposed public key using Shor's algorithm, the 1994 algorithm that remains the canonical example of what a quantum machine can achieve that a classical machine cannot. Pruden assessed the assets at risk at approximately $2.3 trillion. "In a very real sense, someone with a sufficiently powerful and capable quantum computer sort of possesses everyone's digital assets or bitcoins for the public key they can see," Pruden said.
The Path Forward: From Research to Production
The way forward, Pruden said, is to introduce a new signature scheme into Bitcoin that does not rely on the classical mathematics underpinning the Elliptic Curve Digital Signature Algorithm (ECDSA) it uses today. The National Institute of Standards and Technology has standardized post-quantum schemes based on hash functions and lattices, he noted, and discussions within the Bitcoin community tend to favor the hash-based option. BIP-360, proposed last year, laid groundwork for adding a quantum-resistant Taproot output type, and Blockstream has deployed a hash-based signature scheme on its Liquid network. "Turning research into actual production is, I think, what we really need to focus on," Pruden said. "Let's focus on the D in R&D."
Harder Than Taproot: All Hands on Deck
The migration will be significantly harder than the Taproot upgrade, Pruden warned. "Taproot took five years, but that's not even really the full challenge this will represent." Where Taproot was opt-in and most users never bothered to migrate, every bitcoin holder as well as every wallet, exchange, and institution handling the asset will need to participate in a post-quantum migration. Pruden said the timing risk is acute: if a quantum computer arrives before users have migrated, an attacker could front-run pending transactions within a single block interval by paying higher fees to capture funds whose private keys they just derived.
The Sleeping Bitcoin Dilemma
When asked about the unresolved debate regarding dormant bitcoins in addresses vulnerable to quantum attack—including more than 5 million coins attributed to Satoshi Nakamoto via the so-called "Patoshi" pattern of early miner blocks—Pruden urged the community to defer that conflict and focus on the migration itself. "The question of Satoshi's coins in particular is tricky," Pruden said, as it pits two philosophical commitments against each other: Bitcoin's fixed-supply ethos and its commitment to digital property rights. Asked for his personal view, Pruden said dormant coins could potentially be "reintroduced at the tail end of the supply curve" to extend Bitcoin's mining incentive duration after the block subsidy runs out.