Many cryptocurrencies are forced to implement either a fee-for-service model or a proof-of-work model. In fee-for-service models such as Siacoin, users pay for the services that they use. While fee-for-service models are effective at reducing Sybil attacks, they drive many users away from the system especially when similar services are available for free. Proof-of-work systems such as those used in Hashcash and Nano require users to calculate a small proof- of-work before sending a message or transaction. These small proof-of-work systems can be more egalitarian than the fee-for-service model but can be vulnerable to attackers who possess large amounts of computing power.