  Peer-to-peer (p2p) content delivery is promising to reduce the cost of
traditional CDNs and complement the decentralized storage networks such as
Filecoin. However, reliable p2p delivery requires proper enforcement of
delivery fairness, i.e., the deliverers should be rewarded according to their
in-time delivery. Unfortunately, most existing studies on delivery fairness are
based on non-cooperative game-theoretic assumptions that are arguably
unrealistic in the ad-hoc p2p setting. We for the first time put forth the
expressive yet still minimalist securities for p2p content delivery, and give
two efficient solutions FairDownload and FairStream via the blockchain for p2p
downloading and p2p streaming scenarios, respectively. Our designs not only
guarantee delivery fairness to ensure deliverers be paid (nearly) proportional
to his in-time delivery, but also ensure the content consumers and content
providers to be fairly treated. The fairness of each party can be guaranteed
when the other two parties collude to arbitrarily misbehave. Moreover, the
systems are efficient in the sense of attaining asymptotically optimal on-chain
costs and optimal deliverer communication. We implement the protocols to build
the prototype systems atop the Ethereum Ropsten network. Extensive experiments
done in LAN and WAN settings showcase their high practicality.
