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I have an external hard drive with a couple hundred gigabytes of backups (music, photos, video, etc). I want someone I know to back it up on their hard drive, but I want to password protect my files on his hard drive. What is the best way to do this? I'm running Mac OS X 10.6 (Snow Leopard).

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for Windows you could use a password-protected .zip archive -- I don't know of anything like that for Mac though – Nate Koppenhaver Nov 3 '11 at 3:40

Duplicity can do remote backups where the files are encrypted at the destination. Everything is controlled from the client end.

It is posix compliant so will work on OSX, there are tutorials around to get it installed.

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Duplicity is more for remote backups and kinda overkill this just needs a encrypted disk image that Mac OS can easily created without the hassle of PGP and crap. – OliverS Nov 3 '11 at 9:11
That is fine if it is a one time deal, but it is hardly a backup if you only do it once. Duplicity will allow for updating the backup remotely so is a far more robust ongoing solution. – Paul Nov 3 '11 at 22:09
True, duplicity is the only solution for incremental backups. Depends on Mason if it is a once every 6 months thing or every week. – OliverS Nov 4 '11 at 9:34

If you are in a pure Mac OS X environment just use Ken's solution, but if you want to read the files on Linux and Windows as well, try TrueCrypt.

It lets you also create encrypted disk images but has versions for Linux and Windows as well.

  • Create encrypted image
  • Mount image
  • Copy files to be encrypted on the mounted drive
  • Unmount the image
  • Copy the disk image to your friends drive

Only disadvantage of the disk image approach is, when you add a new file no matter how small, you have to copy the complete 100GB to your friend's drive again. If you need delta logic to only copy the modified bytes, have a look at Paul's answer and Duplicity.

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Create an encrypted disk image: it mounts like a disk, and is password-protected. Put your files in there and make as many copies as you want; give them to whomever.

The disk image can be a single file, or a bundle (Sparse Bundle Disk Image). Like app bundles, Finder will show them as a single thing, but in reality it's a directory with multiple files (called "bands"). Because it's sparse, it grows as you put stuff in it. Because it's a bundle, it can be backed up more efficiently. With a single monolithic file, changing a single bit "on the disk" modifies that file and the whole thing has to be backed up again. With a bundle, only the bands that change have to be copied. Also, a bundle may be stored on a disk formatted with FAT32, because the bands are much smaller than the single-file size limit; yet it can still store a dozen-GB file.

On the external drive, create one disk image or many, organized however you want. The size of the images should allow for future expansion; you can move the images to larger and larger external drives over time. Make backups of your files. Unmount/eject the external drive, and the bundles it contains are unmounted at the same time.

Give the drive to the friend, who can then copy the .sparsebundle "files". If they're savvy, they can do an rsync on subsequent backups to minimize the copying. Note that if they put their copy onto a disk that is backed up by Time Machine, the bundle will also be backed up efficiently.

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Have you considered CrashPlan? The free product seems to fit your requirements quite nicely. It's pretty simple to set up. Both you and your friend install CrashPlan and set up accounts. Then your friend gives you the Backup Code for his machine, and then you can configure it to be a backup destination. Your files are backed up over the internet automatically. You should be able to first back up to an external drive, which you can then take over to your friend's house and hook up to his computer and use as a backup destination. I have not personally tested this "seeding" feature, but anecdotal evidence seems to support that it works fine. CrashPlan is cross-platform, supporting Windows, Mac OS X, and Linux.

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I suggest you use ENCFS.

Make a long password, create an encrypted folder and mount it.

That's all, now you can start copying your files to the mounted folder.

When you umount it nobody will be able to see your data until you mount it again.

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