In this article rewritten and translated into Spanish, we explore the theoretical limits of mechanism design in transaction fee markets known as TFMs. Under the title UIC, MIC, and OCA Walk Into a Bar… and Break Mechanism Design, we present in a clear and accessible way how the combination of three desirable properties leads to a fundamental contradiction when blocks are of finite size.
First, we define the three key properties. The User Incentive Compatibility (UIC) property requires that users have no incentive to lie about their valuations or payment priorities. The Miner Incentive Compatibility (MIC) property requires that miners cannot improve their utility by deviating from the protocol, for example through reordering, censorship, or replacement of transactions. Off Chain Attack Proofness (OCA proofness) seeks immunity against off-chain attacks in which external actors or collusions exploit payment dynamics to extract value.
Based on the conceptual tool of Myerson's lemma adapted to the TFM context, we characterize the payment rules that enable truthfulness. Myerson's lemma describes how allocation and payment rules must be structured so that agents report their preferences in a dominant manner. When attempting to simultaneously impose UIC, MIC, and OCA proofness, tensions arise that we examine through a series of auxiliary lemmas.
A first lemma shows that any mechanism granting payments that depend too heavily on block composition creates externalities between transactions. Those externalities open opportunities for miners to change the order or include and exclude transactions in order to increase their total payment, violating MIC. Another lemma demonstrates that if miners' capacity is limited, then certain forms of payment induce incentives for users to manipulate their bids, breaking UIC.
Combining these results, the argument culminates in an impossibility theorem formulated as Theorem 6.9. The theorem establishes that no truthful mechanism exists that simultaneously satisfies UIC, MIC, and OCA proofness when block size is finite. The proof reveals a cycle of contradictions: the restrictions necessary for UIC force payments that miners can exploit, while ensuring MIC restricts the family of payments to the point of offering off-chain attack windows that break OCA proofness.
The implications are practical and profound for auction and mechanism design in blockchains. There is no single recipe that guarantees truthfulness, full alignment of miner incentives, and perfect resistance to off-chain attacks in real environments with limited blocks. Therefore, designers must prioritize and manage trade-offs. Some alternatives include relaxing full truthfulness to approximately truthful incentivization, introducing cryptographic or economic penalties for miners, using hybrid mechanisms with off-chain layers, or accepting limits on resistance against certain attacks in exchange for better guarantees for users.
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