Proof-of-Spacetime (PoSt) is a cryptographic primitive or protocol used in some blockchain systems. In this protocol, a client (in this case, the system) asks a prover (usually a miner or storage provider) to show that they have been storing some data over a period of time.
The core idea is to enable decentralized networks to verify that a specific amount of information is being stored over time without the need to transmit or check that information. This is crucial in blockchains that incentivize decentralized storage, like Filecoin, where nodes are rewarded for storing data over a duration of time.
It’s an extension to Proof-of-Space (PoS) protocols, which only demonstrate that a prover has a certain amount of disk space available at a certain point in time. Proof-of-Spacetime extends this to ensure that the prover continues to store this data over a period of time.