Feature request: Public key encryption of chunks similar to Duplicacy

[dfloyd888]

One feature that has been helpful when it comes to security on Duplicacy is that the actual chunk data is encrypted, even though the hashes are still available to use for deduplication. This ensures that host A can back up to the repository, but doesn't have the ability to restore, so it can't see what other hosts can do. This is useful, especially if the key could be moved to a hardware device like a Yubikey, to ensure a solid layer of security even if the backup repository password is compromised.