Hashed keys are actually fully quantum secure

The discussion revolves around an innovative approach to enhancing the security of Bitcoin transactions against quantum attacks, as proposed by Martin Habovštiak. The method involves a two-step transaction process where a user initially commits to a Quantum-Resistant (QR) signature in a primary transaction. This commitment demonstrates the ownership of the QR private key without revealing any sensitive information that could be vulnerable to theft. In a subsequent transaction, the user spends both the original Pay to Public Key Hash (P2PKH) output and the QR output simultaneously. This dual spending reveals the QR signature and is designed with specific rules to prevent the old output from being independently spent, thus ensuring its security.

The proposed mechanism aims to address the potential threat of quantum computing to Bitcoin's cryptographic security by making it practically impossible for an attacker to either forge a QR signature or to alter the blockchain to revert past the initial transaction's confirmation. This approach not only provides a robust defense mechanism against quantum-enabled theft but also navigates the delicate balance between temporary freezing of assets—seen as a lesser evil compared to their permanent loss—and maintaining the cryptocurrency's reputation.

Several technical queries arise from this proposal, highlighting areas that require further elaboration or development. There is a question about how the QR signature commitment would be encoded into the blockchain and verified during transactions, which might necessitate the introduction of new operational codes or script functionalities for checking these commitments. Additionally, there is curiosity regarding the enforcement mechanism ensuring that the original P2PKH output can only be expended alongside the QR output. This part of the implementation suggests the need for a soft fork of the Bitcoin protocol, prompting inquiries about the specific consensus changes that would be required to facilitate this security feature.

Through this exchange, it becomes evident that while the concept introduces a promising avenue for enhancing Bitcoin's resilience against quantum computing threats, it also opens up a range of technical challenges and considerations that need thorough exploration and resolution within the developer community.