Quantum-proof Bitcoin signatures would clog network nodes with 10x larger data

Coinbase’s push to prepare Bitcoin for quantum computing addresses what happens when a wallet returns from an old backup or a signing server fails.Brian Armstrong called on Oct. 20 for preparation and collaboration across the industry. The operational detail comes from Shashank Agrawal’s Oct. 13 Coinbase article, which asks prospective signature schemes to work with ordinary wallets, recovery procedures, and independently operating custody servers.SHRINCS, a draft hash-based signature scheme for Bitcoin, combines smaller signatures that require a reliable record of previous signing with a larger fallback that works without that record. Under its current rules, recovery with uncertain state means taking the larger path.That preserves a route to signing for someone who can recover the secret. The bargain is that keeping the smaller signatures requires additional operational discipline.The recovery test reaches wallets and exchangesThe current SHRINCS specification lists a 48-byte public key, stateful signatures between 548 and 4,619 bytes, and a stateless signature of 5,777 bytes.“State” is the changing record of which one-time signing slots a key has already used. SHRINCS’ compact c...