The game-theory problems of PQ sunsetting modes

The complexities of implementing a sunset fork in the context of cryptocurrency blockchains, especially when dealing with company-specific quantum-resistant cryptosystems (CQRC), are significant. The presence of CQRCs introduces a high level of uncertainty due to various incentive structures that could potentially sabotage the effectiveness of such forks. It is noted that as soon as a blockchain incorporates even one CQRC, challenges related to deep chain history examinations become prevalent. When multiple CQRCs are involved, there arises an incentive for entities to expend more in transaction fees to reorganize the blockchain to their advantage, thus undermining the concept of chain finality.

Mining strategies and economic implications of blockchain reorganizations further complicate the scenario. Miners might engage in activities like halting their mining efforts on the authentic chain, which users have migrated to, and instead focus on mining a revisionist chain starting from an older block. This strategy involves significant risk and investment, as the payoff only materializes if the revisionist chain's cumulative proof-of-work eventually surpasses that of the authentic chain. During this period, the more established chain continues without the support of these miners, potentially leading to idle honest validator nodes.

Moreover, the potential for large miners to exploit this setup by short-selling coins from the authentic chain and reinvesting in the revisionist chain is highlighted. Such actions could lead to double-spending and acquiring new coinbase rewards if the revisionist chain prevails. However, these maneuvers might also result in the rollback of previously settled transactions, causing dissatisfaction among exchanges and possibly devaluing the currency itself.

One proposed solution to mitigate these risks involves the implementation of periodic checkpoints that are secured by PQ-safe public keys. These checkpoints would be recognized by consensus and finalized by signatures from a specified percentage of these secure keys. This mechanism would effectively limit the depth to which a mining coalition can alter the blockchain, thereby capping the potential budget available for economically motivated reorganizations. This idea, while still preliminary, suggests a direction towards enhancing blockchain security against coordinated attacks involving CQRCs and ambitious miner coalitions.

In conclusion, the discussion reflects a deep concern over the incentive structures and potential economic consequences brought about by the integration of quantum-resistant mechanisms within existing blockchain frameworks. The exploration of new designs like PQ-safe signing algorithms and secure checkpoint systems indicates ongoing efforts to find robust solutions to these emerging challenges.