[DigitalToday reporter Yoonseo Lee] Cryptocurrency exchange Coinbase has proposed a compromise for dealing with coins left unattended during a transition to quantum-resistant addresses, after assessing that bitcoin vulnerable to quantum attacks could total about 7 million BTC.

Coinbase on June 15 released a report by an independent advisory committee that reviewed quantum computing and bitcoin governance, CoinPost, a blockchain media outlet, reported.

The report said a substantial amount of bitcoin could be vulnerable to quantum attacks, particularly in older P2PK-format addresses and addresses whose public keys are already exposed on the blockchain. It viewed adding quantum-resistant signatures to the blockchain itself as a "solvable technical problem." It said the real issue is how to handle assets that are not moved to new addresses by the transition deadline.

The issue is also tied to the bitcoin network's basic principles. The report cited as a representative case that early mined bitcoin, believed to be owned by Satoshi Nakamoto, is stored in P2PK addresses. Letting a third party arbitrarily freeze such coins or move them to safer addresses could spark controversy over infringement of property rights.

The report said views on abandoned bitcoin broadly split into two camps. One argues they should be burned by a set deadline. That view reflects concern that if an attacker using quantum computers steals those holdings, it could lead to funding for malicious states or a sharp price drop from large-scale selling in the market.

The opposing view prioritises ownership. It argues that even if quantum-resistant addresses are prepared, each holder should decide whether to move funds, and that network-level freezing or confiscation could undermine bitcoin's non-censorship principle.

The Coinbase advisory committee proposed an approach combining three measures as a middle ground between the two positions. The first is an "hourglass protocol." It would cap the amount of bitcoin that can be moved from P2PK addresses per block, aiming to reduce the risk of stolen coins flooding the market at once and amplifying price shocks.

The second is applying BIP-361. This measure focuses on phasing out legacy addresses and signature schemes vulnerable to quantum attacks. It also leaves a relief mechanism for some older wallets. The report proposed that if ownership can be proved using zero-knowledge proofs (ZK), holders should be able to move bitcoin even after existing methods are blocked.

The third is Provable Address Control Timestamps, or PACTs. It uses bitcoin's timestamp function to pre-schedule future transfers. It is designed to allow funds to be moved even after the current signature format is no longer valid.

In the market, discussion of quantum security is spreading beyond a technical issue to concerns about supply shocks and changes to network rules. The report acknowledged that handling abandoned assets is not easy, but stressed that technical implementation to introduce post-quantum signatures should proceed immediately. It said preparation for the quantum-resistant transition can no longer be delayed, separate from any consensus on whether to freeze assets.

Concerns about holdings with exposed public keys have also resurfaced. A cited Glassnode analysis estimated that 6.04 million BTC, about 30 percent of issued bitcoin supply, is already in an exposed-public-key state. The basis for that figure may differ from the roughly 7 million BTC cited in the Coinbase report, but both point to older address structures and public-key exposure as central to quantum risk.

The key point to watch is likely to shift more toward governance consensus than technical implementation. Even if a new quantum-resistant address system is introduced, the bitcoin network's principles and market impact could change depending on how long holders are given to transfer existing coins and what restrictions are imposed on assets that miss the deadline. The report put weight on a compromise combining phased retirement, limits on transfer speed and mechanisms to prove ownership, rather than choosing solely between burning and leaving assets untouched.

JUST IN: A Coinbase-backed quantum report estimates around 7 million BTC could be vulnerable to future quantum attacks, including roughly 5 million BTC linked to reused addresses. The report urges the Bitcoin ecosystem to begin migration planning now as quantum-resistant… pic.twitter.com/NUXQdG93Cd