COINBASE IS BUILDING QUANTUM-PROOF CUSTODY FOR A SIGNATURE SCHEME BITCOIN HAS NOT CHOSEN — ITS OWN COUNCIL COUNTS 1.7 MILLION COINS ALREADY SITTING IN EXPOSED ADDRESSES

Yehuda Lindell runs cryptography at Coinbase, and he is building for a decision nobody has made. “It’s unlikely that there will be a single signing scheme that everybody will use,” he told Decrypt. “That means we have to be prepared and ready for the different outcomes on different blockchains.” The design is a fallback: post-quantum threshold decryption sitting behind programmable security modules, so the custody can be pointed at whichever scheme a chain picks later.

That is an honest answer to an open question, and it is also an admission. Bitcoin has not chosen its post-quantum signature. The proposals are still drafts. A custodian holding other people’s coins cannot wait for the draft to become a rule, so it builds a shape that can bend.

Coinbase’s own quantum council, announced June 11, put numbers on the exposure: about 1.7 million bitcoin sit in old-style addresses that are directly vulnerable, and roughly 7 million are vulnerable once you count reused addresses. On what to do about coins nobody can move, the council listed the choices, freeze them after a deadline, do nothing, or slow them down, and refused to pick: that, it said, is “for the community to decide.”

Which is the real fight. The cryptography is a hard engineering problem with money behind it and it will get solved. Whether anyone gets to decide that an old address is abandoned is not an engineering problem at all. Coinbase can build custody that bends. The chain cannot. At the time of this writing, bitcoin was $86,273.