If there is cooperation with another client who has the file you could just get the file from them in the first place.

Perhaps the bandwidth between (dropbox + all your syncing devices) is greater than what the conspiring client can provide, so such a scheme may still be beneficial.

I think they could just share the folder with you on Dropbox, allowing you to download it from there.

You don't need to "get" the file from anyone, you just need convince Dropbox to mark your account as having that file.

Maybe I'm missing something. What possible purpose (other than getting the file) could there be to convincing Dropbox that you have a file?

By "get" I just meant download directly, which could be slow and eat a lot of bandwidth. And then if you actually want that file in your Dropbox, you'd eat even more bandwidth doing the upload again. But syncing once from Dropbox is faster than downloading from someone else and then uploading to Dropbox and then waiting for your other computers to sync. And since you don't have to get the file from the original sharer, they don't have to have enough bandwidth to go around, just let Dropbox handle the copying.

Other than? "Having files" is the entire point of Dropbox.

>> You don't need to "get" the file from anyone, you just need convince Dropbox to mark your account as having that file.

That post made it sound like there was a purpose to having the file in dropbox other than getting it.

I think you missed the part where byte 1257 was "randomly chosen"

It depends. If I already have the full file, it's much easier (and efficient) to tell you the value of a random byte and let DB give you the file than having to transfer it all.

If you're dealing on a small scale (e.g. "Hey, icebraining, let me grab that file from you!"), it's going to be easier to just send a share request from your Dropbox account to mine, which has the same end result (flipping an ownership bit in Dropbox's system).

That doesn't really scale, no, but sharing hashes doesn't really either, unless you want to spend a significant amount of time building infrastructure to keep track of who has what files and automate the management of sharing hashes.

Of course, but then you still need infrastructure to figure out who else has the file, how to keep things private, etc. You can't just distribute a hash and be done with it.

I didn't miss that part, I was simply saying that a client that had the file could tell what byte 1257 was to the other client (or some other random byte, as requested by dropbox).