  Community networks are prone to free-riders, i.e., participants who take
advantage of cooperation from others' routers but do not contribute
reciprocally. In this paper, we present HARPIA, a system for credit-based
incentive mechanisms for data forwarding in community networks aimed to prevent
selfish behavior. HARPIA does not require a trusted third-party or
tamper-resistant security modules as in other incentive mechanisms. Instead, it
uses a distributed accounting scheme (DPIFA) to estimate the balance of data
forwarding contribution and consumption of each network router and settle
correspondent cryptocurrency debts on an Ethereum smart contract. On-chain
settlement transactions are performed every HARPIA cycle (e.g., daily, weekly,
monthly) and must be validated by at least m-of-n network routers using a
multi-signature scheme (MuSig). We also realized a performance evaluation,
security threat assessment, and cryptocurrency costs estimation. Results show
that our proposal is suitable for community networks with up to 64
infrastructure routers under specific m-of-n MuSig thresholds.
