Coinbase Lays Out Post-Quantum Needs for Bitcoin Custody

Coinbase says a future BTC signature design should account for transaction fees, full-node validation costs and the limits of block space.

Coinbase, the custodian holding about 5% of all BTC, published a technical blog on October 13 outlining what it wants from Bitcoin’s move to quantum-resistant security.

Its central point is that choosing a new digital signature scheme is only one piece of the job, since any plan also has to fit Bitcoin’s scarce block space and work for custodians and everyday wallets.

Work to Begin Before Quantum Threat Is Certain

In the blog post, the exchange said it is already preparing its own systems, convening talks with Bitcoin developers and backing open-source work through the Bitcoin Security Consortium.

The company pointed to P2MR, proposed in BIP-360, and P2TRv2 as possible output designs that could accommodate future post-quantum signature systems without requiring a complete redesign each time the cryptography changes.

It also proposed evaluating hybrid arrangements in which a wallet could spend funds through either a conventional ECDSA/Schnorr signature or a post-quantum key during the transition.

Coinbase raised particular concerns about stateful post-quantum signatures. Although these schemes can be smaller and faster than stateless alternatives, reusing signing state can make forgery possible. The company warned that recovering from failed updates or lost state could be difficult for exchanges running multiple signing servers, as well as individuals managing their own wallets.