To allocate transactions to blocks, cryptocurrencies use an auction-like transaction fee mechanism (TFM). A conjecture of Roughgarden [44] asks whether there is a TFM that is incentive compatible for both the users and the miner, and is also resistant to off-chain agreements (OCAs) between these parties, a collusion notion that captures the ability of users and the miner to jointly deviate for profit. The work of Chung and Shi [12] tackles the problem using the different collusion resistance notion of side-channel proofness (SCP), and shows an impossibility given this notion. We show that OCA-proofness and SCP are different, with SCP being strictly stronger. We then fully characterize the intersection of deterministic dominant strategy incentive-compatible (DSIC) and OCA-proof mechanisms, as well as deterministic MMIC and OCA-proof ones, and use this characterization to show that only the trivial mechanism is DSIC, myopic miner incentive-compatible (MMIC) and OCA-proof. We also show that a randomized mechanism can be at most 0.842-efficient in the worst case, and that the impossibility of a non-trivial DSIC, MMIC and OCA-proof extends to a couple of natural classes of randomized mechanisms.

翻译：为将交易分配至区块，加密货币采用类似拍卖的交易费用机制（TFM）。Roughgarden [44] 提出一个猜想：是否存在一种TFM，既能对用户和矿工同时实现激励相容性，又能抵抗双方之间的链下协议（OCA）——这种合谋概念刻画了用户与矿工联合牟利的能力。Chung与Shi [12] 的研究基于另一种合谋抵抗概念——侧信道证明性（SCP）来探讨该问题，并在此概念下证明了不可能性结果。我们证明OCA抗性和SCP存在本质差异，且SCP严格强于前者。随后，我们完整刻画了确定性占优策略激励相容（DSIC）且OCA抗性机制，以及确定性MMIC且OCA抗性机制的交集，并利用该刻画证明：仅平凡机制能同时满足DSIC、短视矿工激励相容（MMIC）及OCA抗性。我们还证明，随机化机制在最坏情况下效率最多为0.842，且非平凡DSIC、MMIC与OCA抗性机制的不可实现性可推广至若干自然类别的随机化机制。