Aligning privacy incentives in P2MR

The recent discussion in the Bitcoin Development Mailing List highlights some critical considerations concerning the development and implementation of rescue protocols in blockchain technology, particularly in response to potential quantum computing threats. The dialogue underscores the importance of preparing for scenarios where migration to post-quantum (PQ) cryptographic outputs may be lackluster. Despite the advancements in making newer cryptographic methods like P2TR cheaper and more private, there remains a realistic possibility that adoption could be underwhelming. Thus, optimizing our systems to handle a quantum disaster recovery scenario is deemed essential, as it appears increasingly plausible and its severe impacts can be mitigated at a relatively low cost.

Rescue protocols, contrary to discouraging PQ migration, might actually promote it by retroactively securing vulnerable unspent transaction outputs (UTXOs) into PQ-safe ones. This mechanism is particularly crucial even if no one initially adopts the PQ output type since it ensures the preservation of ownership at rates comparable to immediate mass migration to PQ outputs. Moreover, these protocols can effectively address the more challenging segment of the market—coins that possess no quantum-hard knowledge asymmetries, such as those held in older wallet types or by potentially deceased users, whose keys might be lost.

Regarding the technical deployment of these rescue protocols, there is a preference for implementing them through a soft fork, which tightens existing rules rather than relaxing them. This approach would require all EC spends to also satisfy the new rescue protocol conditions alongside current consensus rules. However, the feasibility of integrating various rescue protocols into a cohesive system without creating complexities still requires thorough research. A promising direction involves developing a generalized two-step proof system that can validate any quantum-hard relation and verify the spender's knowledge of the related witness, though this remains an open problem.

This ongoing conversation reflects a proactive approach in the Bitcoin community towards safeguarding digital assets against emerging quantum threats and ensuring the resilience of blockchain technology in diverse future scenarios. The commitment to maintaining 'neutral internet money' amidst evolving technological landscapes is evident, emphasizing the need for continuous innovation and adaptation in blockchain security practices.