stoRNA: Stateless Transparent Proofs of Storage-time

Proof of Storage-time (PoSt) is a cryptographic primitive that enables a server to demonstrate non-interactive continuous availability of outsourced data in a publicly verifiable way. This notion was first introduced by Filecoin to secure their Blockchain-based decentralized storage marketplace, using expensive SNARKs to compact proofs. Recent work employs the notion of trapdoor delay function to address the problem of compact PoSt without SNARKs. This approach however entails statefulness and non-transparency, while it requires an expensive pre-processing phase by the client. All of the above renders their solution impractical for decentralized storage marketplaces, leaving the stateless trapdoor-free PoSt with reduced setup costs as an open problem. In this work, we present stateless and transparent PoSt constructions using probabilistic sampling and a new Merkle variant commitment. In the process of enabling adjustable prover difficulty, we then propose a multi-prover construction to diminish the CPU work each prover is required to do. Both schemes feature a fast setup phase and logarithmic verification time and bandwidth with the end-to-end setup, prove, and verification costs lower than the existing solutions