the problem with this theory is that deduplication works so well with file backup as the largest files we have are most often music and video, something that is highly replicated amongst file sharing users. i.e millions of users have the same Beatles album. Yet, when each persons album is encrypted it will be entirely different than every other persons album. If they were in any way similar it was not correctly encrypted. Thus the hit rate will be almost negligible. So than you say OK, but maybe the block level code of the encryption of my Beatles album is similar to the block level code of the encryption of my Eminem album, and than we can save storage there. The problem with this is that encryption algorithms aim to make their input files output as close to a random distribution as possible. Meaning not only are those two copies of the beetles albums going to be as different from each other, but they will be different from any other file. To sum it up, a well encrypted file should be uniformly random -> meaning it is uncompressible - > two different uniformly random files are still random relative to each other and when put together still cannot be compressed.