Proof-of-Spacetime (PoSt) is a consensus mechanism that requires a network participant to prove they have dedicated a storage space to maintain a copy of certain information over a period of time. In PoW-based protocols such as Bitcoin and Ethereum, “work” is done by solving complex mathematical puzzles using vast amounts of computational resources ( generating sufficient hash power) before a single block reward is issued.
While the cost of accumulating these computing resources is rewarded in PoW-based protocols, PoSt consensus protocols reward the cost of storage to honest miners.
How does the Proof of Spacetime confirm that given data is stored over time?
In a Proof-of-Spacetime (PoSt) consensus protocol, two cryptographic hash puzzles (known as WinningPoSt and WindowPoSt) are issued to test any blockchain user involved in the network . These two challenges are such that a miner can only solve them correctly if a given data has been stored over a period of time.
The WinningPoSt challenge selects a miner expected to mine the next block at random, queries them for a copy of the blockchain data and expects an answer to be returned within a short time frame. The short time frame given for the answer guarantees the miner maintained a copy of the data.
On the other hand, the WindowPoSt challenge ensures the copy of the data is continually maintained by repeatedly requesting the data be provided in specific time intervals. This works because it is considerably more expensive to quickly seal a copy of the data every time it is queried.
In summary, the WinningPoSt challenge verifies the copy of the data when a participant is chosen to mine the next block, and the WindowPoSt challenge verifies the data is continually present.