Clear DefinitionsProof-of-Space and Time
1 min read
Pronunciation
[proof uhv speys and tahym]
Analogy
Imagine a lottery where your chances of winning depend on how much shelf space in your warehouse (Proof-of-Space) you've filled with special, pre-calculated lottery numbers. When a draw happens, you quickly check your stored numbers. If you find a potential winner, you then have to take that potential winning ticket to a special, slow, but verifiable 'time-stamping machine' (Proof-of-Time / VDF) that takes a fixed amount of time to process. Only after this time-stamping can you claim your prize. This prevents people from quickly trying many tickets or predicting winners too far in advance.
Definition
A consensus mechanism that combines Proof-of-Space (PoSpace), where miners allocate hard drive capacity to store data ('plots'), with Proof-of-Time (PoTime), which uses a Verifiable Delay Function (VDF) to ensure a delay between block productions. This aims to be more energy-efficient than Proof-of-Work and more decentralized than some Proof-of-Stake variants.
Key Points
Combines Proof-of-Space (PoSpace) with Proof-of-Time (PoTime).
Miners (farmers) dedicate disk space to storing cryptographic 'plots'.
A challenge is issued, and farmers search their plots for a qualifying PoSpace proof.
The best PoSpace proofs are then run through a Verifiable Delay Function (VDF) for PoTime, introducing a delay.
The farmer whose VDF output is first or meets certain criteria wins the right to create a block.
Aims for energy efficiency (like PoSpace/PoC) and resistance to certain attacks (via PoTime).
Example
Chia Network is the most prominent example of a blockchain using Proof-of-Space and Time. Farmers 'plot' their hard drives and then 'farm' by responding to challenges with proofs of space that are then processed through VDFs.
Technical Deep Dive
In PoST, farmers first create plots using a computationally intensive process. Then, for each block challenge, they quickly scan these plots. If a plot contains a good proof for the current challenge, this proof is broadcast. A small number of the best proofs are selected and submitted to VDFs. The VDF introduces a verifiable delay, and the output of the VDF determines the block winner. The PoTime component (VDF) helps prevent grinding attacks (where miners try to optimize plots for future challenges) and ensures a more regular block time.
Security Warning
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