Crypto glossary
Proof of space and time
Proof of space and time is a consensus design that uses allocated disk storage instead of computing power to choose who adds the next block.
In proof of space, participants fill hard drives with large precomputed files called plots. When a new block is needed, the network issues a challenge and farmers check their plots for the best matching answer; more storage means more chances to win. Proof of time, a verifiable delay function, adds a sequential computation so that blocks cannot be produced faster than real time.
Chia, launched in 2021 by BitTorrent creator Bram Cohen, is the best-known network using the model, and its participants are called farmers rather than miners. The pitch is lower energy use than proof of work, since checking a plot costs almost nothing once it is written, and the use of hardware many people already own.
In practice, Chia's launch caused a shortage of large hard drives and SSDs, and creating plots wore out solid-state drives quickly. Storage-based consensus still favours whoever controls the most capacity, so industrial farms emerged much as they did in mining. Proof of space is also distinct from storage networks that pay for keeping useful data.
Example
A farmer with 100 TB of plots receives a challenge, finds the closest proof in a fraction of a second and has a proportionally larger chance of winning the block reward than someone with 1 TB.