Posts tagged mobileme

Online storage services like iDisk (part of MobileMe) or DropBox are very convenient for sharing and backing up files–but when you put files into the cloud you’re assuming that:

• those companies, and
• all their employees, and
• all their contractors, and
• all their collocation facility employees

will be morally upstanding. And that they will securely erase old drives. And that their systems will never be cracked. Ever.

My point is that sensitive stuff, like tax documents and passwords, must be encrypted before storing them in the cloud.

The solution? Make an encrypted file on your computer that can be mounted as a “secure hard drive”.

(Update August 2009): TrueCrypt is an easy-to-use and cross-platform solution to this issue. The following is a tutorial that is a Mac OS X specific alternative to TrueCrypt.

Example disk image

Using the disk image is easy — when you double click your encrypted disk image, you’ll be prompted for the image’s password, and then the image will be mounted, looking just like another hard drive was attached to your computer. (With TrueCrypt you must “mount” the file using the TrueCrypt software, so it isn’t quite as user-friendly).

You can drag-and-drop private files into the disk image, and even edit them just like a normal disk. When you’re done, eject the drive, and your files won’t be readable until the image’s password is re-entered.

The disk image can be stored on your MobileMe drive for backups, but you make sure you un-mount/eject the drive before you lose your network connection to prevent the disk image from losing your most recent changes.

So — here’s how to create one of these encrypted disk images.

Mac OS X Disk Utility

1. Open Disk Utility (found in /Applications/Utilities/)
2. Click “New Image” in the toolbar
3. The “Save As:” field will be the name of the disk image file, so it should be something like “secret.dmg” or “private.dmg.”
4. The “Volume Name:” is what the name of the disk will be when it’s mounted.
5. A volume size of 100 MB should be fine if you’re just storing documents–and you can resize the image later if you need to.
6. Choose Mac OS Extended (Case-sensitive, Journaled)
7. Choose 256-bit AES encryption
8. Choose No partition map
9. Choose read/write disk image
10. And finally click Create

Settings in Disk Utility to create an encrypted disk image

I’d recommend NOT storing the password in your keychain, so when asked for the password for the disk image, unselect that option, and make sure you remember the password to your new image–because you can’t open it without the password.

Disk Utility will automatically mount the disk image as soon as it’s created. Remember to eject it when you’re done (by right-clicking on the disk image and choosing “Eject”). In the future double-click the image to re-mount it and get access to your secret files again.