It doesn't really make sense to encrypt the keys, but store the secret
literally in the same directory. uploadkeys will now be stored in
plaintext. The branch `legacy` has the old code from before this commit.
Since keygen.py is run as root, uploadkeys is owned by root. This causes
issues when imgupload.py tries to chmod the uploadkeys file since it
doesn't have permissions to chmod it.
Solution: remove UPLOADKEYS_CHMOD option
