Coinbase, holding about 5% of BTC, set out what it wants from Bitcoin's post-quantum shift, favoring flexible outputs like P2MR and asking about late movers.
Key Facts
Coinbase, which holds about 5% of all Bitcoin, published its views on Tuesday on how the network could move to quantum-resistant signatures.
The exchange backed flexible output designs such as P2MR, proposed in BIP-360, and floated a transition design in which funds can be spent with either a classical or a post-quantum key.
Coinbase called the post an input to an open discussion, not a final position, and said it would be useful to consider whether wallets that migrate late could still move funds.
Coinbase, which holds about 5% of all Bitcoin (BTC), set out on Tuesday what it would want from a move to signatures that can withstand quantum computers, including output designs flexible enough to add or replace post-quantum schemes later.
The post details what one of the world's largest crypto custodians would need from an upgrade to replace the signature schemes that a powerful enough quantum computer could break.
"It is intended as an input to an open discussion, not a set of instructions or a final Coinbase position," Coinbase's Shashank Agrawal wrote in the blog post.
Coinbase says it is preparing for risks posed by quantum computing. Source: CoinMarketCap
"Coinbase believes that Bitcoin will continue to be the most trusted crypto-currency in a post-quantum world, and we also recognize that the migration will be a challenging, complex, and multi-year process," the post said.
Coinbase favored output designs that would let new post-quantum digital signature schemes be added or swapped later without a complete redesign. It named P2MR, proposed in Bitcoin Improvement Proposal 360, or BIP-360, and P2TRv2 as options that appear to offer that flexibility.
For the transition itself, it floated a "1-of-2" design in which the same funds could be spent with either a classical ECDSA or Schnorr key or a post-quantum key.
Coinbase Seeks MPC-Friendly Signatures, Path for Late Movers
Coinbase's custody business shapes several of its other points.
"For Coinbase and many of our customers, MPC-friendliness is an important consideration in the choice of PQ schemes," the post said, referring to multi-party computation, which splits signing among several parties.
It said managing state in signatures "is notoriously error-prone and could even lead to forgery," and asked for a stateless option if stateful schemes are supported.
Coinbase also said it would be useful to consider whether and how users who miss any future cutoff for older signatures could move their funds afterward. It said legacy funds, including Satoshi-era holdings and older outputs with exposed public keys, "are best treated as a separate governance and engineering problem."
Coinbase, Stanford University's Dan Boneh and Localhost Research hosted a post-quantum Bitcoin workshop at Stanford, according to a September post. It is also one of the nine firms that unveiled the Bitcoin Security Consortium, which committed $15 million over three years, in July.
Other networks have set timelines. Zcash developers are targeting January for quantum-resistant payments.
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