I want to efficiently back up an encrypted copy of my hard drive. I am currently using rsync to backup an unencrypted copy, and I find it quite efficient.
I looked at duplicity and rsyncrypto, but duplicity makes incremental backups, and rsyncrypto uses a unique key for each encrypted file. Duplicity also ran out of memory, and I would need to backup the rsyncrypto keys somewhere. I find these to be space-inefficient, so I don't want to use them.
What I think would work well is if I could loopback/bind mount / and backup the encrypted mountpoint. I looked at eCryptfs and EncFS, but they both seem to only mount encrypted directories, and not allow encrypting a mounted directory. They both support encrypting the filename, which is also a desirable feature.
If I could have an encrypted version of my file system, then my existing rsync-backup would work efficiently. When very little has changed, only the file names need to be encrypted.
Is there a way to encrypt a mounted directory as another directory? Any other suggestions?