A Post Quantum Migration Proposal

The discussion revolves around a strategic approach to enhancing the security of a blockchain system against potential quantum computing threats through a phased deployment plan, which includes phases A, B, and C. The conversation highlights the flexibility of this plan, allowing for adjustments based on the progress of quantum computing advancements or the development speed of the zk-STARK proof system intended for phase C. This adaptability is crucial, especially considering the possibility of merging phases B and C if conditions permit, to streamline the deployment process. However, concerns are raised regarding the permanent restrictions imposed by phase A on sending to pre-quantum addresses, suggesting that a revision could be necessary to avoid a hard fork in the future.

A specific technical challenge discussed is the treatment of BIP360 P2QRH addresses in this phased approach. These addresses, which can contain EC signature spending conditions, might face restrictions under phase B's rules, potentially leading to the accidental locking of funds until phase C is implemented. This scenario underlines the necessity of careful consideration in how these addresses are managed, particularly in preventing funds from being irretrievably locked due to the enforcement of stricter rules before the full quantum-resistant solution is in place.

The dialogue further explores the implications of restricting Elliptic Curve (EC) spending from P2QRH UTXOs. A suggestion is made that phase B should universally restrict EC spending across all script types to safeguard users' assets until phase C introduces a robust quantum-resistant framework. To mitigate potential challenges arising from these restrictions, standardizing P2QRH address derivation and encouraging the use of addresses that include at least one post-quantum spending path are proposed. This measure, coupled with providing libraries to generate addresses with ML-DSA and SLH-DSA leafs, aims to ensure users do not inadvertently create addresses that could lock their funds or expose them to quantum attacks.