This already existed in a way via Millchan on Zeronet.
>>15280
An idea that I had to fix this was to split every file into two parts, a "file" and a "key", with checks on both sender and recipient to make sure that no user ever possessed both the key and file for the same object at the same time, and that when a file was browsed by a user only then would the network also seek out the key and decode it. But it had to be implemented in a particular way. You can't just encrypt a file because possessing "encrypted CP" is still CP, so the idea was that the file would actually be split somehow, like a pattern of alternating bytes, such that the "file" and "key" were each half of the completed object and not merely an encoding scheme applied to the whole.