[thotypous]

This is really interesting!

How does Sia prevent hosts from precomputing the checksums to fake they are behaving but erasing the data itself? Does it checksum over random ranges of data?

Which source does it use for entropy so that the network remains distributed but nodes can't predict the ranges? Does it use the last block nonce?

Which checksum algorithm does it use? Is care taken as to not be vulnerable to prepend or append attacks from hosts who intend to host data partially whilst pretending they are hosting full data?

[Taek]

Sia founder here. The hashing algorithm we use is blake2b. Definitely secure.

We do probabilistic proofs, so we have the host provide us a small random sampling of actual data (so the host can't rely on precomputing), plus a proof that this actual data is what the contract says the host should be storing.

See chapter 5: https://sia.tech/sia.pdf

[Fornax96]

I'm not entirely sure on the specifics of storage proofs, but as far as I know it's something along these lines:

When uploading data the renter (that's what we call the node which pays for storage) computes a merkle tree of the data which the host should be storing. When a contract is nearing its end the host will enter a proof window of 144 blocks (1 full day) in which it will need to prove that it is storing the renter's data. The proof is probably based on the block hash of the block where the window started. The host stores the proof in the blockchain and the renter will be able to see the transaction. If the proof matches the merkle tree (which the renter has stored) the contract will end and the host will receive the payment and their collateral back. If the proof is invalid or was not submitted at all the renter can cancel the contract which destroys the funds in it. The host won't get paid and loses its collateral, but the renter also won't get their money back (to discourage the renter from playing foul)

There is some more info on this on the wiki: https://siawiki.tech/about/trustlessness and the website: https://sia.tech/technology. And here is some incomplete technical documentation: https://gitlab.com/NebulousLabs/Sia/-/blob/master/doc/Resour...

If you want to go more in-depth you can go on our Discord where lots of developers hang out, eager to help others to get started with the network :) https://discordapp.com/invite/sia

EDIT: The whitepaper is of course the best source of knowledge. It's quite old at this point but the core principles still apply https://sia.tech/sia.pdf