Securing Private Data On Your Mac Using An Encrypted Disk Image

Last modified
Wednesday, February 24, 2021

Though I’m not always the best writer, I do enjoy writing down my thoughts from time to time. There’s just one problem with that. It’s not secure.

Sure, there are all kinds of apps for the mac and your I device that allow you to journal. However, most of the apps I have seen are only somewhat usable, or just way too fancy for what I want to do. I played with the MacJournal app for the mac a few months ago, but I was not impressed. It would always crash on me while I was writing, and I finally just tossed it out the window, so to speak. So, now, what to do?

I had a few personal documents scattered around the mac, well in the documents folder of course, but I was always afraid of prying eyes. OK, I understand what some are thinking. Turn off your computer when your not using it, and you will be fine. Yes, this is true, and for the most part I do. There’s always just that one part of me that has always wanted to take that extra step. So, how can we make our files and important data more secure? Enter the encrypted disc image.

In simple terms, it is a partition you create that is… Well… Encrypted. Once created, you may access the DMG file at any time, just like you would any other DMG, or disc image file. You enter your Password, and a new volume appears on your desktop, allowing you to save and write data, just as you would anywhere. Once your finished, you simply eject the volume, and your data is secure. For now, I see this as the best solution for keeping private data secure. Plus, if you do not have the funds to spend on extra software to secure private data, this is the perfect solution, as this way is totally free.

So, how do we do this? Let me start off by saying, this is a very simple process, even if your not real advanced with the Mac. It’s just a matter of following the prompts.

  1. Open the utilities folder with the keystroke, Command plus Shift Plus U. The Utilities folder is under the Applications folder in case anyone is wondering.
  2. Locate the Disc Utility, and press Command plus O to open it.
  3. Press Command-N to open the dialog to create a new blank disk image.
  4. You will be placed in the save as name field. Obviously, this is where we name the image. Give the image a name that is meaningful to you. For the purpose of this guide, let’s call it “TechTips” Excluding the quotes of course. From here, we will want to use our VO commands. That is, VO right, and VO Left arrows.
  5. VO Right to the normal popup menu that asks where you want to save your image. It should default to Desktop. If not, choose it from the popup menu, or simply press Command Shift D to choose Desktop. VO right until you land in another name field. Give it the same name as in step four, TechTips. This ensures that the volume inside the disc image has the same name as the image itself. If you decided to put something else in this field, the volume will have a different name. For instance, in step four, we put “TechTips” in the save as field. Let’s say you decide to put the name “AppleVis” in this second name box. When the image is created, the DMG will say “TechTips” and the volume you see once your image is successfully open will say “AppleVis”. So to avoid confusion, I would recommend the same name in both fields. In this case, it’s “TechTips”
  6. VO right, and you will land on a textfield that defaults to 100 MB. This is where we enter the size of the image. You can give it a size by typing X.00 where X is the number for the size of the partition, followed by either MB or GB, depending on how big you want your image to be.
  7. VO right to the popup menu that should default to “APFS Format”. If it does not default, VO space and choose this option from the menu.
  8. VO Right to the popup that is the Encryption menu. it defaults to none. You may choose either 128-bit AES encryption, or 256-bit AES encryption. The former is recommended, and the latter is slower, but more secure. Choose whatever works for you. Note: The next two steps have to do with the technical details of the partition. I understand the basic concept of a partition, but that is all. Because of this, I have left the other popup buttons in the dialog in their default states. If anyone who knows more about these options wants to comment, please do so.
  9. After choosing an encryption option, you will be asked to give your image a password. Make sure it’s a good secure Password, then click Choose. Note: If you forget your password, there is no way to access your encrypted image, Nor is there a way to recover your lost password. Make sure it’s a password you will remember.

After you enter your password, and click Choose, the computer will inform you that it is creating the image. This may take a little while depending on what you select, so be patient.

Once your image is created, it will appear on your Desktop as TechTips.dmg, provided you gave it the same name as in this guide. Also, your newly created volume itself will appear as well. Note that the volume only appears once automatically just after creation. Anytime you want to access it in the future after it has been ejected, you will need to go through the steps. CMD Plus O on this image, and you will be asked for your password. When entered correctly, your volume will magically appear on the Desktop, just like a thumb drive. Move, copy, delete, and create just like normal.

Some final thoughts.

When your done with your encrypted volume session, make sure to eject the volume, either by VO Shift M and choosing the eject option, or by simply pressing CMD plus E on the volume. Your volume will disappear, leaving the DMG image file intact. When you open it again, everything will be just as you left it.

Important, make sure you do not loose your DMG file, or you will not be able to access your encrypted volume at all. Have fun.


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