(There's been some progress on getting proof-of-replication working, but it's still early stages and I haven't seen anything on proof-of-spacetime.)

Also, the economics of FileCoin don't make a lot of sense ... https://blog.dshr.org/2018/06/the-four-most-expensive-words-...

I just dug it up and they say Proof of Replication is going great. But don't show anything, they promise to open the code in the 'coming months' so people might see what progress has been done if any.

No progress was mentioned for Proof of Spacetime.

Edit: The link to their update, the only substantial one since the ICO last year I think... https://filecoin.io/blog/update-2018-q1-q2/

They wrote a paper describing a plausible system that - if it existed - could do a thing. They've been much less successful actually finding a way to implement it.

You can probably do it by mixing the data with some extra data so replicated copies actually look different so you have to do proof of possession on each replica, and you dont even know they are replicas.

GP suggests making each copy unique. It seems to me that the difficult part is making it cheap for uploaders, verifiers and downloaders to translate between the original data and the various unique copies, without also making it cheap for storers to do so (otherwise they could just store the original data and generate parts of the copies on the fly when challenged).

A similar problem arises in memory-hard functions used for password hashing, such as scrypt and Argon2. Those functions are designed to ensure that you have to use a large amount of memory to compute the function - or at least, to ensure that a space/time tradeoff that allows you to use a smaller amount of memory is very expensive. I wonder if techniques from memory-hard functions could be useful in proof of (unique) storage?