"Locking" an external hard drive

Reader Dustin Kuo is interested in locking down an external hard drive. He writes:

Is there a software that can lock the external hard drive so if someone got hold of it, they wouldn’t be able to view the data?

I wish that waving a magic wand over your drive and barking “Lock!” could work this minor miracle but, alas, even with such a wand and Christopher Plummer’s commanding voice you’re not going to realize the results you’re after.

What you need to do is create an encrypted space on all or a portion of that drive and then move the files you want to protect into it. You have a number of ways to do that.

One is built into Mac OS X. Open Disk Utility, choose File -> New -> Blank Disk Image and in the resulting window choose Sparse Disk Image from the Image Format pop-up menu and either 128-bit AES Encryption or 256-bit AES Encryption from the Encryption pop-up menu. Then choose a size from the Size pop-up menu (select Custom and then enter a size if the preconfigured sizes don’t suit you). Name the image, choose to save it on your external drive, and click the Create button. You’ll be prompted for a password. Enter and verify that password and click OK and you have a protected image that can be opened only with your password. Move your files into this image and you're good to go.

Note that you should choose to not store this password in your keychain if you’re all that concerned about security. Also, this image will take up only as much space as the accumulated content inside it. So, even if you’ve asked for a 5GB image file, if you put 1GB worth of files in it, the image will be only 1GB. You can then add files until you reach that 5GB limit, at which point, the image is full.

Another free option is the open-source TrueCrypt. This is a cross-platform encryption tool that you can use to encrypt folders and volumes. Again, if you intend to encrypt an entire external hard drive you’ll first have to move the files off that drive, format it with TrueCrypt, create an encrypted volume, and then copy your files to that volume. TrueCrypt features more encryption schemes than does Disk Utility.

And then there’s the $35 Knox, which our resident Gemeister Dan Frakes tells me is the goods. Like Disk Utility, it creates images using either the 128- or 256-bit AES standard. Unlike with Disk Utility or TrueCrypt, you can use Spotlight to search the contents of a Knox image (termed a “vault”). (You can search the image only when it’s open.) And Knox includes a backup feature.

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