## Cryptology ePrint Archive: Report 2016/035

Proofs of Space-Time and Rational Proofs of Storage

Tal Moran and Ilan Orlov

Abstract: We introduce a new cryptographic primitive: Proofs of Space-Time (PoSTs) and construct a practical protocol for implementing these proofs. A PoST allows a prover to convince a verifier that she spent a spacetime'' resource (storing data---space---over a period of time). Formally, we define the PoST resource as a linear tradeoff between CPU work and space-time (under reasonable cost assumptions, a rational user will prefer to use the lower-cost space-time resource over CPU work).

Compared to a proof-of-work, a PoST requires less energy use, as the difficulty'' can be increased by extending the time period over which data is stored without increasing computation costs. Our definition is very similar to Proofs of Space'' [ePrint 2013/796, 2013/805] but, unlike the previous definitions, takes into account amortization attacks and storage duration. Moreover, our protocol uses a very different (and simpler) technique, making use of the fact that we explicitly allow a space-time tradeoff.

Category / Keywords: cryptographic protocols / proofs of work, proofs of space, bitcoin, crypto-currency