A warning has been issued that major blockchains such as Bitcoin and Ethereum must immediately begin preparations to shift to counter threats from quantum computers.

On June 11 (all times local), blockchain outlet Decrypt reported that Coinbase's quantum computing and blockchain advisory committee said in a new report that discussions on the technological transition should not be delayed further.

The report focuses less on the technology itself than on the problem of handling coins left behind during the transition. The biggest issue is how to deal with bitcoin that is not moved to quantum-resistant addresses. The committee estimated that about 7 million bitcoin could be vulnerable to future quantum attacks when combining legacy addresses where public keys have already been exposed with cases of address reuse.

The committee explained that a large portion of these coins may be believed to be Satoshi's coins, or funds whose owners may have already lost their keys. Such coins are difficult to migrate to a quantum-resistant system unless holders move them themselves. That means consensus is needed on whether the network will forcibly freeze or burn vulnerable coins, or leave the choice to users.

The report also presented three options for handling coins that are not moved. One approach discussed was permanently freezing or burning vulnerable coins after a certain deadline. It also included a scenario of taking no separate action and leaving it to users' judgment. The committee, however, pointed out that forced burning could "infringe on property rights and could set a precedent for network-level intervention that conflicts with Bitcoin's core principles."

It also proposed an intermediate compromise. Options include limiting the amount of vulnerable coins that can be moved per block, or accepting separate cryptographic proofs instead of existing signatures. In that case, users can prove their intention to transition in advance without moving funds publicly.

This warning comes as major blockchains have already begun discussing quantum-resistant transitions. The Ethereum Foundation formed a team in January to coordinate Ethereum's quantum-security transition and has been reviewing ways to replace validator and wallet signatures with quantum-resistant alternatives. In February, Vitalik Buterin (비탈릭 부테린) presented a quantum upgrade roadmap.

Coinbase's advisory committee also warned in April that proof-of-stake networks such as Ethereum and Solana could be particularly vulnerable. That is because validator signatures protecting these networks rely on cryptographic systems that could eventually be broken by quantum computers. The Stellar Development Foundation also published a roadmap to migrate users to quantum-safe cryptographic systems.

Against this backdrop, internal discussions within Bitcoin are becoming more sensitive. Bitcoin, by structure, has a significant amount left in older addresses, and how the network handles coins that do not move affects both property rights and protocol principles. Coinbase previously said, "The right time to prepare for a cryptographic transition is just before it becomes urgent," adding, "Customer assets are safe as of today, but just because it is not imminent does not mean it is not important."

Ultimately, the issue is less about when quantum computers emerge than about what transition rules are put in place beforehand. Bitcoin developers are continuing discussions on how to move vulnerable coins to quantum-resistant addresses and on standards for handling coins that ultimately do not move.