PQC output type discussion

The integration of CISA into the P2TRv2 bundle poses significant challenges and considerations, particularly in terms of its impact on the adoption timeline and user experience. Introducing CISA from the outset could potentially delay the availability of P2TRv2, which might decrease its adoption prior to the critical Q-day. This is a concern since the benefits of fee incentives might not sufficiently offset the drawbacks of a delayed rollout.

From a technical standpoint, one proposed solution to mitigate these risks involves designing version 2 of SegWit (Segregated Witness) to allow for a later soft fork that incorporates CISA. This approach would prevent the necessity for another version bump, streamlining the update process. In terms of practical implementation, once wallets incorporate CISA, they could facilitate a seamless migration of coins to the new system without causing noticeable disruptions for users. Moreover, this strategy would avoid fragmenting the anonymity set, maintaining privacy and security standards across transactions.

Further technical suggestions include allocating a single bit of the public key to denote it as 'anyone-can-spend', which could be set by default in all wallets following the CISA update. Alternatively, adding an additional byte and removing x-only keys has been considered, utilizing the remaining seven bits as flags. However, both methods raise concerns regarding their effect on anonymity, as well as potential implications for revealing wallet capabilities through such flags. These considerations underscore the need for careful planning and design in the development of blockchain technologies to balance functionality, user experience, and security.