Giving teeth to expected EC disabling: P2XX(-T)(-ML)

In recent discussions within the Bitcoin development community, there has been an exploration into enhancing the security and robustness of new output types such as P2TRv2 through the implementation of mechanisms that could automatically disable Elliptic Curve (EC) opcodes/paths. This consideration is driven by the anticipation of quantum computing developments that might compromise current cryptographic practices. Notably, the P2TRv2 was designed with a soft expectation that a future softfork would disable these EC opcodes/paths to secure the network against potential cryptographic vulnerabilities.

Two primary proposals have been put forward to facilitate this automatic disabling: the Tripwire and Miner Lockdown mechanisms. The Tripwire approach involves using a specific transaction type as a trigger; for instance, the presence of a NUMS point spend in a transaction would immediately deactivate EC opcodes/paths from the next block. This method, suggested by Tadge Dryja, sets a definitive boundary on the timeline for the disabling, ensuring it's not delayed indefinitely. On the other hand, the Miner Lockdown allows for a majority of the mining hashrate to initiate the disabling, providing a quicker response option to emerging threats, as discussed by Sjors Provoost in offline forums.

The integration of these mechanisms does introduce additional complexity but is argued to be beneficial. For example, the Tripwire ensures that any user can unilaterally enforce the disabling, which could encourage broader testing and adoption of Post-Quantum Cryptographic (PQC) methods necessary for future-proofing coins. This proactive approach not only enhances security but also aligns with the decentralized ethos of cryptocurrency by enabling users to participate directly in critical consensus decisions.

Furthermore, by integrating these mechanisms directly into the consensus rules, rather than relying on future commitments or plans, the network can ensure that these protections are reliably enacted when needed, without requiring further agreement or additional forks. This strategy helps mitigate risks associated with the evolving landscape of quantum computing and its potential impact on cryptographic systems currently in use within blockchain technologies.