Guest Post :: How to Protect Files on USB Drives

Today, I am pleased to present a guest post from one of my readers, Robert E. Nuddleman, Esq. of San Jose, California which explains how to protect files on USB "thumb" drives.  Robert has used Macs in his practice for about six years, and he says that he is "continually amazed with the performance versus Windows."  He is also a blogger, and you should check out his Employment Law Blog.  Without further adieu, here is Robert's guest post:

Many attorneys use USB thumb drives to transport files from one computer to another.  As the federal government can tell you, however, losing the thumb drive can have serious consequences.  You do not want to face disciplinary proceedings because that confidential memo was lost and recovered by someone savvy enough to get it into the wrong hands.  The best option is to encrypt the data on the thumbdrive.

While there are a plethora of programs and methods for protecting files on a USB thumb drive if you are using a Windows machine, there are very few options for Mac users.  You can find a third party program on versiontracker.com or you can create an encrypted disk image using Mac’s native Disk Utility.  After I tried a couple of third party programs I was not satisfied so I decided to give Disk Utility a try.  After reading a few tutorials, I figured it out and it’s a lot easier than I thought.

Launching into the how-to, it can be helpful to understand Disk Images.  If you ever downloaded a Mac program and installed it, you are familiar with Disk Images.  A Disk Image is a .dmg file that contains the applications or documents that you drag and drop into your applications folder. A Disk Image acts like a folder where you can put files, applications, folders, etc.  Disk Images have many uses, including creating an encrypted file that you can use to transfer confidential information.

So, here’s how to create an encrypted Disk Image on your thumbdrive that you can use to easily transport confidential information.  Please note that I am running OS X 10.3.9, and the exact method may be a little different if you are running OS X 10.4.

1. Put your thumbdrive into your USB port.
2. Open Disk Utility (under Applications --> Utilities).
3. From the top menu, choose Images, then New, then Blank Image.
4. In the "Save As" box, choose the file name for your Disk Image.  I like to use the size of the Disk Image as a file name because I have several different-sized thumbdrives and I have a different Disk Image for each drive.
5. Choose where you will save the Disk Image file.  I like to save it right onto the thumbdrive, but you can save it to your harddrive and copy it later if you’d like.  If you are saving it directly to your thumbdrive, it may be a good idea to remove any files from the thumbdrive.
6. On the "Size" dropdown menu, I usually choose "Custom" and then designate the size of the file.  There are defaults for various sizes.  I like to make the Disk Image slightly smaller than the full capacity of the thumbdrive (i.e., if I have a 1 gigabyte drive I will make a 900 megabyte Disk Image).  That way I can transfer some files without using the disk image if I want.  You can choose any size file you want and you can place more than one Disk Image on your thumbdrive.
7. Under "Encryption", choose AES-128.  This is a fairly high level of encryption.  The federal government certified AES-128 for classified information at the secret level.  Top Secret requires AES-192 or AES-156, but 128-bit encryption is plenty powerful.
8. Under "Format", choose read/write Disk Image, then click on "Create".
9. Disk Utility will create the Disk Image and ask you for a password.  Choose your password carefully because if you lose the password you will not be able to recover the data.  You have to input the password twice to make sure you don’t make any mistakes.  Secure passwords do not use words that can be found in a dictionary and are best if they have a combination of upper case letters, lower case letters, numbers and symbols.
10. You can choose to add the password to your keychain, which will mean you do not have to input the password to open the file when attached to the computer you used to create the Disk Image, but you will have to input the password to open the file on any other computer.  If you do not add the password to your keychain, you will have to input the password every time you open the Disk Image even if you open it with the computer you used to create the Disk Image.
11. Your Disk Image is now complete so you can close Disk Utilities.

When you open the Finder, you will see the newly created Disk Image mounted on your system (i.e., it will have an eject button that will unmount the drive when you are done).  You can now drag and drop any files you want onto the Disk Image.  You can work directly off the Disk Image so you don’t have to worry about copying the files back and forth. Simply open the files the same way you would as if it were on any other drive.

When you are done, you simply eject the Disk Image.  Note: You must eject the Disk Image before you eject the USB drive.  Otherwise you’ll get a warning telling you that the Disk is in use.  You can now carry your USB thumbdrive without worrying about falling into the wrong hands.

Comments

[Victor Medina]

Great post. Extremely useful information and something that I didn't already know. Thanks - VJM

[Stacey Warren]

Great post! Any idea how this affects the USB drive if it's used on a Windows PC?

I keep a so-called "CommonPlace" book (a fancy term for an all-in-one reference list/journal/to do list) on my USB drive in a TiddlyWiki, which is basically a hyperlinked, souped-up text file. The beauty of it is that it lets me easily transport my data back and forth between my home iMac (love it) and my office Windows laptop (detest it).

Any idea whether encrypting the USB drive data via your Mac method would affect the ability to access it when plugged into a PC?

Love your blog. I keep it on my list of "must-reads" in Bloglines.

[rob quackenbush]

Thank you...this is just the information I was looking for!

[San Francisco Doctor]

Superb post, thank you. Worked like a charm. I am always "shuttling" between my office and home computer so I keep ALL my documents on a thumb drive so they are with me when I need them. Your suggestions just made things a lot more secure. You would think Mac would want to explain this process in detail, but the Disk Utility help file is of little value. Your instructions were spot on and easy to follow.
Bravo!

[Bentley Skeie]

Thanks!

I just did this. The only item I would add is to make sure your thumbdrive is formatted for Mac OS Extended.

I tried this first with the drive formatted for Fat32 and the disk image would not copy or be created. Once I reformatted to Mac OS Extended, it worked like a charm.