Sparse Image Dialog Box

Sparse Image: A Secure Disk Image For Your Mac

The Sparse Image is a very robust and pretty much hidden in the Mac OS X Disk Utility program.  When you create a Sparse Image, you create an encrypted password protected disk image.  You can use the disk image to store private files, documents, photos, and other data.

There are other programs that work similar to Sparse ImageTrueCrypt (discussed here: is the most popular example; however,  Sparse Image has this functional difference with TrueCrypt:

  • With TrueCrypt you specify the size of the image, and the total size of the image is dedicated on your hard drive.  As a metaphor, with TrueCrypt, you create a secure “container” for your data.
  • When setting up the Sparse Image, you set up the maximum size of the image, but the image itself grows dynamically as you begin to use it for storage.  For example:  a 2.6 GB Sparse Image will begin with only 26 MB of dedicated space on your hard drive.  As the 26 MB space begins to fill, the Sparse Image will begin to take more hard drive real-estate until the maximum allocation of 2.6 GB is reached. Unlike TrueCrypt, the container created by Sparse Image is elastic, expanding as you need it, and capping off at its maximum size.

To create a Sparse Image, go to Disk Utilities, and choose File> New> Blank Disk Image.  This dialog box will appear:

Sparse Image Dialog BoxDo the following in the New Blank Image dialog box:

  1. Enter the name for the Sparse Image you are creating in the Save As dialog box.
  2. Choose where you want to save your Sparse Image.  I suggest the Desktop.  It makes it easier to open the disk image.
  3. From the drop down dialog box, choose the maximum Size (Cd and DVD references are used to help you evaluate sizes) you want for the Sparse Image.
  4. Select the level of encryption to be used.  The recommended 128 Bit AES will work fine.  For those paranoid about security, a 256 Bit AES is offered, though some performance penalties will result.
  5. Choose Sparse Disk Image as the image format.
  6. Click the Create button.
  7. Another dialog box opens asking you make up a secure password and type it twice.  DO NOT place this password on your Keychain (uncheck the Keychain access box below your passwords).  If you store the password with Keychain access, no password will be needed to open the Sparse Image.
  8. Click the Create button.

Now, on your desktop is a disk image file icon with the name you provided, and the tag “.sparseimage”.  Double click the icon.  A dialog box appears requesting your password.  Supply it, and click OK.  An icon appears on your desktop that is named Disk Image.  Double click it.  A window opens.  You now can treat this space just like any other space on your hard drive:  add or delete files, copy, drag and drop, create folders, etc.  When you are done, eject the disk image, and all your data is stored securely.  Should you decide at some point you no longer need the Sparse Image you created, simply delete it, and the disk image, and anything saved on it will be gone.

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