Coinbase Maps Bitcoin’s Post-Quantum Security Path as It Holds 5% of Supply

For the transition itself, Coinbase favors staged protection. One option is a “1-of-2” hybrid output in which the same funds carry two spending paths: one authorized by a classical ECDSA or Schnorr key and one by a post-quantum key. Users could keep signing classically today and switch to quantum-resistant signing when required. On scheme selection, Coinbase wants an evaluation set spanning standardized and in-progress algorithms — ML-DSA, SLH-DSA and FN-DSA — plus compact candidates such as SHRINCS, while warning that stateful schemes carry a sharp risk: reusing signing state can enable forgery.

The Coins That Cannot Move

The hardest part of the migration is not the cryptography but the funds that may never be migrated. Coinbase argues legacy coins should be treated as a separate governance and engineering problem, distinct from adding post-quantum signature support. That category includes pay-to-public-key outputs with permanently exposed keys, reused addresses, dormant holdings, and Satoshi-era balances, alongside the possibility of covert quantum theft before the public learns a CRQC exists.

It is the same exposure problem that Europol has flagged for exposed wallet keys. Coinbase says any rescue mechanism — whether based on seed knowledge, zero-knowledge proofs, or rate-limiting tripwires — must itself be quantum-safe, so a quantum attacker holding only a public key cannot exploit the recovery path. The exchange leaves the question open, arguing the discussion can run alongside the signature work rather than delaying it.