The security of the Bitcoin system is based on having a large amount of computational power in the hands of honest miners. Such miners are incentivized to join the system and validate transactions by the payments issued by the protocol to anyone who creates blocks. As new bitcoins creation rate decreases (halving every 4 years), the revenue derived from transaction fees start to have an increasingly important role. We argue that Bitcoins current fee market does not extract revenue well when blocks are not congested. This effect has implications for the scalability debate: revenue from transaction fees may decrease if block size is increased. The current mechanism is a pay your bid auction in which included transactions pay the amount they suggested. We propose two alternative auction mechanisms: The Monopolistic Price Mechanism, and the Random Sampling Optimal Price Mechanism (due to Goldberg et al.). In the monopolistic price mechanism, the miner chooses the number of accepted transactions in the block, and all transactions pay exactly the smallest bid included in the block. The mechanism thus sets the block size dynamically (up to a bound required for fast block propagation and other security concerns). We show, using analysis and simulations, that this mechanism extracts revenue better from users, and that it is nearly incentive compatible: the profit due to strategic bidding relative to honest biding decreases as the number of bidders grows. Users can then simply set their bids truthfully to exactly the amount they are willing to pay to transact, and do not need to utilize fee estimate mechanisms, do not resort to bid shading and do not need to adjust transaction fees (via replace-by-fee mechanisms) if the mempool grows. We discuss these and other properties of our mechanisms, and explore various desired properties of fee market mechanisms for crypto-currencies.
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