Just read the reappeared sourcecode (assuming it works as advertised): The hash is an SHA256 of pure 4MB blocks in the input file. They add no message type information which could prevent mixups between Dropbox-deduplication hashes and hashes computed for other purposes.
The following dropship file was assembled using only shasum, ls and vi:
The following dropship file was assembled using only shasum, ls and vi:
Could someone who has never shared files with me verify that it indeed produces a picture of a beach?