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You probably have sensitive data on your MacBook or iMac. That data might live in a folder that contains various files with company secrets or your own personal information. Unencrypted, that folder can be viewed by anyone with access to your desktop or laptop.
However, if you encrypt that folder, only those with the decryption password are able to access the contents within.
What is encryption? Simply put, encryption is the process of encoding information such that the information can only be viewed with the key (think "password") that was used to encrypt the data. This is called decryption and until that data is decrypted, it cannot be read. If you are the only person holding the decryption key, it means only you can unlock the data.
Also: The best encryption software: Protect your data
You can achieve folder encryption with a third-party application, but there's also a built-in tool that can do this for you. Said tool is Disk Utility, and it makes encrypting existing folders on your MacOS machine very easy.
The caveat to the method I will outline is that it creates an encrypted image from the folder and leaves the original intact. On top of this, once you've created the encrypted image, you cannot add new items to it. Because of this, the method is really best suited for either encrypted backups or encrypting folders that will not need to be changed. However, if you really want to protect that data, you would create the encrypted image and then delete the original folder, otherwise anyone could still view the contents (if they have access to your desktop).
Let me show you how it's done.
The only thing you'll need for this is an updated version of MacOS running on either a MacBook or iMac. I'll be demonstrating on a MacBook Pro with an Apple Silicone M1 chip and MacOS Monterey (v 12.6).
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I would highly recommend you test out this process on a folder that doesn't contain any important documents. Once you know how to successfully encrypt folders, you can then do so with those folders that do contain important information.
Click the Launchpad icon on your Dock and type Disk Utility. When the Disk Utility launcher appears, click it to open the app.
With Disk Utility open click File > New Image > Image from Folder. When the folder picker popup appears, navigate to and select the folder you want to encrypt, and click Choose.
In the resulting popup window, do the following:
When you select the encryption type, you'll be prompted to type and verify an encryption password. Make sure this password is strong and unique (and not the same as your user password).
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Disk Utility will then encrypt the folder. When it completes, click Done.
Open Finder and navigate to the folder housing the encrypted image. If you double-click on that image (it'll end in .img), you'll be prompted for the password you added during the image creation. Upon successful authentication, Finder will open the image and you can access the contents within.
And that is all there is to create an encrypted folder in MacOS with Disk Utility. Although this option is somewhat limited, it is a good way to keep sensitive information from prying eyes. And if you have no need to add new files and folders to the encrypted image, you can feel free to delete the original folder, so the data contained within cannot be accessed without going through the encrypted image.