Proof-of-space is essentially stored Proof-of-work. You are pre-filling your drive with many cryptographic hash's. When a challenge comes in the software will do a quick check to see if any of your plots could possibly have a proof (a hash with sufficient zeros for that challenge). If any of your plots pass this filter then the plot is looked up on the HDD to check if it does indeed contain a proof. The difficulty, the number of zeros needed for a hash to be considered a proof, adjusts as the network grows to ensure a steady supply of coins. With proof-of-work you are printing lottery tickets every time a challenge comes in, then throwing them away and starting again, with Proof-of-space you are printing your tickets once and then storing them for years. There is extra layers, Chia is actually proof-of-space-and-time, so that you can't win by faking proof-of-space with proof-of-work.

For someone uninitiated: what if you had high computing power? Instead of scanning your HDD, can’t you generate these hashes on the spot?

Yes, you can. That's called a grinding attack. There is mitigation in the proof-of-space construction for exactly that. That is also the reason that they will have to move to more expensive proofs as time goes on, and hardware improves.

> with Proof-of-space you are printing your tickets once and then storing them for years.

So then where's the issue with SSD wear, and wouldn't it be more interesting for people to have spinning drives (for the better ratio of GB / $)?

> There is extra layers, Chia is actually proof-of-space-and-time, so that you can't win by faking proof-of-space with proof-of-work.

Is it because of this? So you'd have to print your lottery tickets often enough that a faster drive may help you?

Yes you absolutely want to be farming with spinning drives for the better price to capacity ratio as you mention! (Hopefully in a few years this will change and SSDs will overtake spinning disks in this metric)

The most efficient way to start your farm is to build your plot with a temporary drive (an SSD) and then move it to a destination drive (Spinning HDD) where the actual farming takes place.

The building of the plot is what does heaps of writes and reads and puts the wear on an SSD.

You absolutely can plot directly to Spinning Disk however it is slow and you will really be trashing the heads if you try and plot multiples to the same disk.

The solution is an enterprise SSD with proper endurance. If a consumer SSD doesn't state it's TBW then you can be pretty sure its not very much.

> wouldn't it be more interesting for people to have spinning drives (for the better ratio of GB / $)?

You do trade off for a slower read rate. If the rate of requests coming in is fast enough, your spinning drive/s may not be fast enough to go through the indexes for each one.

Spinning disks are more than fast enough for farming. Many use network connected spinning disks. Tape drive is not fast enough however.

I'm probably missing something here. CPU/GPU cycles are irreversible, you can't get them back after you have used them. Storage space is reversible, you can get it back at any time by deleting what has been stored. I'm sure they have a way of detecting and preventing this, but wouldn't that imply that constant network connectivity is required to check that the storage is still allocated?

Think of proof of work, where you create loads of hashes for each challenge that comes in, once people came along with ASICs they could create so many more hashes in the same amount of time! The chances of finding a proof with an ASIC is directly correlated with how much more hashes you can create than a CPU in a given time. With proof-of-space you are storing the hashes on disk. The more hashes you have stored the more chance you have of finding a proof. You can delete those hashes at any time if you would like (to use the space for some other purpose) and the only effect is that you will just be lowering your chances of finding a proof for any future challenges. You don't have to be connected to the network all the time, however you will only have a chance of winning Chia while you are connected to the network. The positives of this approach: 1) Once you have plotted you drive and the plots are farming you use very little electricity (many people farm with Rasberry Pi's) 2) You can utilize unused storage on drives you already own and then as you need that space for some other purpose you can delete the plots. 3) Your chances of wining are directly correlated with your share of the network space ie. someone who plots twice as much has you has on average twice the chance of wining a block, no more, no less. 4) Building a special ASIC for proof of work serves no useful benefit beyond what it was intended to do. Whereas if someone was to build a cheaper more efficient form of storage, well that would be a benefit to everyone!

One way is using zero knowledge computational integrity proofs. They allow me to prove to you that I know of pre-image of some hash without revealing what it is.

Say the network has seen 1TB of data before with hash H. It can generate a random number as a challenge, and request a miner to prove they have access to the 1TB worth of pre-image at the same time it has access to the random challenge. The only way for a miner to compute such a proof is to have the 1TB of data stored somewhere.

What you describe is an instance of the Hashcash Proof-of-Work. There are many other types of PoW, which don't amount to just computing a hash function [1].

[1] https://cryptorials.io/beyond-hashcash-proof-work-theres-min...

There are multiple flavors of proof of space and they seem to be based on quite complex math to the extent that a simple explanation may not be possible.

There always is a simple explanation:

Resulting from (1) removing irrelevant details (details crucial for an implementation, but irrelevant for an initial mental model) and (2) making use of analogies built around already known concepts.

"Complex maths" is never an excuse to not find that explanation.

Disclaimer: I am a pure mathematician.

I don’t think I have ever heard of proof of space, is it the same as proof of stake?

Completely different things.

In Proof of Stake, the network (roughly!) allocates rewards for validating transactions based on the amount of coins you have, i.e., your stake in the network.

In Proof of Space, the network allocates rewards based on you proving that you are really storing the data you were supposed to store. If you fail to produce a proof for some data item the network expected you to have stored, you lose the reward.

More info:

https://en.wikipedia.org/wiki/Proof_of_space

https://en.wikipedia.org/wiki/Proof_of_stake

> In Proof of Space, the network allocates rewards based on you proving that you are really storing the data you were supposed to store.

Sort of? But you're usually not really storing data for proof of space. That's a different kind of system.

Yeah, that is called proof of storage in Filecoin:

https://spec.filecoin.io/#section-algorithms.pos

Another important wrinkle is that Chia’s proof-of-space needs you to prove you’ve stored the right cryptographic noise - rather than, for example, any useful data.

Another proof of waste shitcoin. Just what the world needed.

They are different. Chia isn't Proof of Stake because how many XCH has no impact on your odds of winning more.

https://en.wikipedia.org/wiki/Proof_of_space

https://en.wikipedia.org/wiki/Proof_of_stake

Sorry, dropped a couple words: "how many XCH you have has no impact"

No - it’s a bit more like preprinting big ranges of lottery tickets, that require giant look-up tables moreso than raw computation.

So it requires the dedication of some hard/rivalrous real resource, storage space, other than either strictly energy/CPU (PoW) or the protocol’s own tokens (PoStake).

See the Chia ‘Green Paper’ for more details.