Reader Dan, who would like the data on his flash drive to be a little more secure, is just the kind of questioner I like—one who both asks and answers the question. He writes:
After reading Joe Kissell’s piece entitled
Your Apps in your Pocket, I looked around the Web for 2gig flash drives. Most say that they are Mac OS X compatible, but when you read the fine print the software that comes with them (including security software) isn’t. Does this mean that the only way to make sure your data is secure would be to put an encrypted disk image on the flash drive?
In Joe’s article he pointed to
Lexar’s JumpDrive Secure USB Flash Drive as an option because it includes security software for both the Macintosh and Windows. But I understand that those non-Lexar flash drives you find at Costco are mighty tempting.
The short answer to your question is yes, the way to do it is to create an encrypted disk image, load the stuff you want onto that disk image, and copy it to the flash drive.
The long answer is, here’s how:
1. Launch Disk Utility.
2. Click the New Image button in the toolbar.
3. In the sheet that appears select a size for your disk image (a number of presets are offered in the Size pop-up menu but by clicking Custom you can create a disk image of any size you like).
4. From the Encryption pop-up menu choose AES-128 and leave the Format pop-up menu at Read/Write Disk Image.
5. Name the image in the Save As field and click Create.
6. An Authenticate dialog box will appear. Enter and verify a password for your disk image and click OK.
If you’d like to save yourself a few steps along the way, download a copy of Jaan Patterson’s
safeThis. This utility provides a slicker front end to OS X’s built-in disk encryption technology.
An additional note: When you decrypt that disk image you’ll be offered the option to add the password to the connected Mac’s keychain. Allowing this will make the whole setup less secure if both your laptop and flash drive are stored in the same bag and stolen. To be safe rather than sorry, don’t add the password to the keychain (and carry the flash drive somewhere other than your laptop bag).