Proof-of-Space-Time (PoST) is a novel consensus algorithm that aims to replace the energy-intensive Proof-of-Work (PoW) scheme used by Bitcoin and other cryptocurrencies. PoST allows a network participant to prove that they have allocated a certain amount of storage space for a certain period of time, without requiring much computation or electricity. In this blog post, we will explain the basic idea and benefits of PoST, as well as some of the challenges and open questions.

The motivation behind PoST is to use a more environmentally friendly and scalable resource as a payment for participating in a decentralized network. PoW requires participants to compete for solving hard cryptographic puzzles, which consumes a lot of CPU power and electricity. This leads to high operational costs, centralization risks, and environmental concerns. PoST, on the other hand, uses storage space as the main resource, which is cheaper, more abundant, and more distributed than CPU power.

Moreover, PoST can adjust the difficulty of the proof by varying the time duration of the storage, rather than increasing the computation complexity. This means that PoST can achieve a similar level of security as PoW with less energy consumption.

The basic idea of PoST is as follows: A participant who wants to join the network must first reserve some storage space on their device and fill it with some random data. Then, they must periodically prove to the network that they are still storing this data and have not modified or deleted it. This proof is called a Proof-of-Space-Time, and it consists of two components: a Proof-of-Space (PoS) and a Proof-of-Time (PoT).

A Proof-of-Space is a proof that shows the participant has reserved a certain amount of storage space and has filled it with some specific data. This can be done by using a hash function that maps the data to a short output, called a commitment. The participant sends this commitment to the network as a proof of their storage allocation.

The network can then challenge the participant to provide some portion of their data that corresponds to their commitment. The participant must respond with the correct data within a short time frame, otherwise they are considered dishonest or offline.

A Proof-of-Time is a proof that shows the participant has kept their storage space unchanged for a certain period of time. This can be done by using a verifiable delay function (VDF) that takes a long time to compute but is easy to verify. The participant applies this function to their commitment and obtains an output, called a proof. The participant sends this proof to the network as a proof of their storage duration. The network can then verify that the proof is correct and matches the commitment, and that it took at least the expected time to compute.

By combining these two components, PoST ensures that the participant has spent both space and time resources to join the network. The more space and time they spend, the more likely they are to be rewarded by the network for their contribution. PoST also prevents participants from cheating by reusing or sharing their storage space with others, or by pre-computing or outsourcing their proofs.

PoST is an elegant and simple solution for achieving consensus in a decentralized network without relying on wasteful computation or electricity. However, it also faces some challenges and open questions that need further research and development.

To participate in a PoST network, a node has to generate and store a large dataset, called a plot, on its disk. The plot consists of cryptographic proofs that are derived from a public parameter, called a challenge. The challenge is periodically updated by the network to ensure that the plots are fresh and valid.

To generate a new block, a node has to submit a proof that it has stored the plot for a certain amount of time, called an epoch. The proof consists of a subset of the plot that matches the current challenge. The node that submits the fastest and most accurate proof wins the right to produce the block and receive the reward.

The network verifies the proof by checking that it corresponds to the challenge and that it is consistent with the previous proofs submitted by the same node. This ensures that the node has not tampered with or deleted its plot during the epoch.

Proof-of-Space-Time has several advantages over other consensus mechanisms:

It is more energy efficient than PoW, as it does not require intensive computations or specialized hardware. It is more secure than PoS, as it does not depend on the distribution of wealth or stake among the participants.

It is more scalable than both PoW and PoS, as it allows for parallel block production and verification, reducing the network latency and increasing the throughput. It is fairer than both PoW and PoS, as it gives equal opportunities to all nodes regardless of their resources or influence.

Proof-of-Space-Time is still an emerging technology that faces some challenges, such as plot generation time, storage cost, and network synchronization. However, it is also a promising solution that could enable more efficient, secure, and inclusive blockchain networks in the future.