Coinbase plans post-quantum Bitcoin custody, compatible with various signature schemes

Coinbase Chief Cryptographer Yehuda Lindell stated on the MARA Foundation TV program that the exchange is designing a custody system capable of adapting to any post-quantum signature scheme that Bitcoin may adopt in the future. It is currently unclear which post-quantum signature scheme Bitcoin will use in practical applications. Lindell believes it is unlikely that a single signature scheme will be universally adopted, so preparations must be made for different outcomes across various blockchains.

Coinbase is custodian for approximately $250 billion in assets for institutions such as BlackRock. Traditional Multi-Party Computation (MPC) relies on key sharding, but many post-quantum signature schemes may be "not friendly to MPC"; for example, hash-based signatures lack the arithmetic structure required for traditional cryptographic key splitting. Although cryptographers like Dan Boneh are researching relevant solutions, this research is still in a highly experimental phase, and it remains uncertain whether a viable MPC-like solution for hash signatures can be developed.

To this end, Coinbase is exploring a backup architecture centered around programmable Hardware Security Modules (HSM), where private keys will be encrypted with post-quantum cryptography and assembled only within physically secure HSMs. Lindell stated that while the completion timeline is uncertain, once finished, "I will be able to say, I can support any scheme," without worrying about a blockchain adopting a signature scheme that it cannot support.