The game-theory problems of PQ sunsetting modes

A notable strategy includes a "tripwire" scenario, where a NUMS puzzle embedded in a honeypot UTXO with Bitcoin rewards is designed to expose quantum computing capabilities by triggering a freeze on all legacy coins once the puzzle is solved. However, this raises questions about the tactical advantage for a quantum entity to reveal its presence when it could instead covertly secure assets. Further complexity arises with the potential collusion between quantum entities and a 51% majority of miners to exclude post-quantum proofs, aiming to access $215 billion worth of legacy P2Pk coins. Such actions would likely shift strategic preferences towards overt over covert operations due to economic incentives such as higher reorganization fees offered by competing quantum entities.

Additionally, sunsetting measures like those proposed in BIP361, which suggests a flag-day activation to enhance security, do not fully mitigate risks such as deep chain reorganizations before activation. This gap allows quantum entities to potentially exploit timing discrepancies between quantum breakthroughs and network responses, thereby increasing coordination costs and highlighting existing informational asymmetries. The removal of checkpoints from Bitcoin software further exacerbates vulnerabilities, exposing the network to potential quantum attacks targeted at legacy coins. There is an urgent need for continued research and development to address these emerging challenges and reassess current security protocols in light of quantum advancements.

The concept of a sunset fork introduces further complexities, particularly when integrating company-specific quantum-resistant cryptosystems (CQRC). The introduction of even a single CQRC can lead to significant uncertainties and incentive structures that may undermine the effectiveness of such forks. For instance, entities might be motivated to pay higher transaction fees to manipulate blockchain reorganization to their benefit, thereby threatening the concept of chain finality. The situation becomes increasingly complicated if miners decide to abandon the established chain for a revisionist one, requiring a higher cumulative proof-of-work to yield returns. This strategy risks major economic fallout, including potential double-spending and dissatisfaction among exchanges should older transactions be negated by successful revisionist mining efforts.

To mitigate these risks, the implementation of secure periodic checkpoints recognized by consensus and finalized through signatures from PQ-safe public keys has been suggested. This approach would restrict the depth to which the blockchain can be altered retrospectively, effectively capping the economic resources available for reorganization. While preliminary, these ideas mark a critical step towards fortifying blockchain integrity against coordinated quantum and miner coalition attacks, reflecting ongoing efforts to adapt and secure blockchain technologies against evolving threats. For more insights into strategies for handling quantum emergencies in blockchain technology, you can reference discussions like those found on Ethereum Research, which explore the feasibility of hard forks in response to quantum threats.