Coinbase lays out flexible designs as key priority for Bitcoin's post-quantum migration

Coinbase published a set of technical priorities for Bitcoin's post-quantum transition, urging the community to begin preparations as it would be a complex, multi-year process.

The exchange, which holds 5% of the total bitcoin Bitcoin (BTC) supply, said it is currently preparing its own systems for a post-quantum future. It stated that protecting the Bitcoin network from quantum threats involves more than selecting a quantum-resistant signature scheme. 

An ideal approach, according to Coinbase, would protect both exposed and newly created funds, fit within Bitcoin's limited block space, preserve independent validation by full nodes, work with institutional custody systems, support ordinary wallets, and provide a credible path for coins that cannot or will not move.

"We believe it is important to begin preparing well ahead of any CRQC (Cryptographically Relevant Quantum Computer) announcement," Coinbase said. "Bitcoin consensus changes and ecosystem migrations can take years, so it is important that we begin this work now."

High-level recommendations

The exchange listed several high-level preferences. It said post-quantum output designs should separate the "container" from the signature scheme, allowing systems to be introduced, replaced, or supplemented without a complete redesign. Coinbase pointed to P2MR (BIP-360) and P2TRv2 as constructions that appear to offer this flexibility. 

Coinbase also said it favors staged protection in which active wallets could use a PQ-capable or hybrid construction before any final policy on legacy signatures is settled. One option it described was a 1-of-2 construction giving the same funds two alternative spending paths, one authorized by a classical ECDSA or Schnorr key and one by a post-quantum key.

On signature schemes, the company said it is important that any support for stateful signatures also include a stateless option, as stateful designs carry risks from state mismanagement that could lead to forgery.

Coinbase further noted that multiparty computation (MPC) friendliness is another important consideration for institutional custody and that at least one viable post-quantum option should have promising MPC compatibility.

"When implemented effectively, MPC can provide strong protection against key theft, and it is an important layer of defense for large organizations that face constant attacks on their infrastructure," Coinbase said.

Regarding abandoned or inaccessible coins, Coinbase said these questions are difficult and deserve debate, but that the discussion can continue in parallel with technical work to add post-quantum signature support. 

"Coinbase believes that Bitcoin will continue to be the most trusted cryptocurrency in a post-quantum world," the exchange said. "We want to contribute to the community's efforts and help create the conditions for careful, sustained progress."