dropship

This is pretty close to how their deduplication used to work, and isn't too different than how rsync works. Of course, this gave rise to the ability to transfer files (even non-public files) quickly between Dropbox accounts provided knowledge of the hashes of its chunks, and Dropbox has since changed their deduplication. See https://github.com/driverdan/dropship

Edit: I now find out that wladimir has had this idea and shipped code on the same idea: https://github.com/driverdan/dropship I have wondered for a while if it could be done without the API by hooking into whatever checksumming is done before uploading. For example, if you were to find a popularly pirated file (for example, a widely distributed MKV of an episode of Break Bad) and copy it to your Dropbox, the upload is instant as there is a high probability that someone has already uploaded it. If you were able to somehow able to hook into Dropbox's checksumming functions it may be possible to report a checksum on a 'fake' non-existent file that is the same as what would be provided by the real copy of the file. The file then appears in Dropbox where you are free to download it at top speed having only known the hash of the file previously

What's yours stays yours. Unless somebody knows the hash. https://github.com/driverdan/dropship

As I've understood it, it's already (partially) reverse-engineered by dropship. https://github.com/driverdan/dropship/blob/master/dropbox/me... Still, I see no reason to use Droxbox servers when you could setup your own.