Tor, the most popular deployed distributed onion routing network, suffers from performance and scalability problems stemming from a lack of incentives for volunteers to contribute. Insufficient capacity limits scalability and harms the anonymity of its users. We introduce LIRA, a lightweight scheme that creates performance incentives for users to contribute bandwidth resources to the Tor network. LIRA uses a novel cryptographic lottery: winners may be guessed with tunable probability by any user or bought in exchange for resource contributions. The traffic of those winning the lottery is prioritized through Tor. The uncertainty of whether a buyer or a guesser is getting priority improves the anonymity of those purchasing winners while the performance incentives encourage contribution. LIRA is more lightweight than prior reward schemes that pay for service and provides better anonymity than schemes that simply give priority to traffic originating from fast relays. We analyze LIRA's efficiency, anonymity, and incentives, present a prototype implementation, and describe experiments that show it indeed improves performance for those servicing the network.
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