Hashed keys are actually fully quantum secure

The discussion opened with the clarification of a common misconception regarding the security of hashed keys in the context of quantum computing threats. It's pointed out that hashed keys, contrary to popular belief, can be secured through a specific scheme even after quantum computers become a viable threat, albeit with some economic cost involved. This proposed method hinges on the use of Quantum Resistant (QR) signing mechanisms and involves a user obtaining bitcoin via external means to pay for transaction fees, which would then be held on a QR script.

The process further detailed entails creating a transaction that commits to a signature of the QR public key alongside a usual spendable output. This setup proves the user’s knowledge of the private key without revealing the public key. After a sufficient number of blocks, the user is required to spend both the old and QR output in a single transaction, where spending the old output alone is deemed invalid. This mechanism is designed to prevent attackers from stealing by making it necessary to revert the blockchain, an action considered infeasible.

A potential weakness identified in this scheme is the treatment of extended public keys (xpubs) as de facto private keys, necessitating their protection for privacy reasons and to avoid being flagged as "dirty" by regulatory agencies, which could lead to them becoming unspendable. The typical non-disclosure of non-extended public keys unless spending occurs was also noted.

Two significant implications of this scheme were highlighted. Firstly, the urgency to develop a quantum-resistant scheme now, in anticipation of quantum computing becoming more mainstream, is less critical than previously thought. Although implementing such measures too late could temporarily freeze assets, this scenario is seen as preferable to outright theft. Secondly, freezing coins in this manner was discussed in terms of morality and the potential reputational harm it could inflict on Bitcoin, especially when considering coins with revealed public keys, though no definitive stance was taken on this matter.

The message concluded with a willingness to support a soft fork that sensibly implements this strategy, underscoring a proactive approach to enhancing Bitcoin's security against quantum computing threats.