If you need to securely email tax documents to your accountant, or store highly sensitive personal files on an external USB flash drive, simply putting them in a standard macOS folder is not safe. If the drive is lost, anyone can plug it in and read the contents. To secure your data, you should use the built-in macOS Disk Utility to create a password-protected, encrypted disk image (.dmg file) that acts like a highly secure digital vault.
How to Create the Encrypted Image
Creating an encrypted disk image does not require any third-party software; the tool is built directly into the core of the macOS operating system.
- Open the Launchpad or use Spotlight Search (Command + Space) to open the Disk Utility application.
- Look at the top menu bar (next to the Apple logo) and click on File.
- Hover over New Image, and select Blank Image… from the drop-down menu.
A complex configuration window will appear. You must carefully configure the settings of your new digital vault.
- Save As: Type a name for the .dmg file itself (e.g.,
Secure_Vault). Choose where you want it saved (like your Desktop). - Size: By default, this is set to 100 MB. You must increase this if you plan to store large video files or thousands of high-resolution photos. (Note: The file will take up this much space on your hard drive immediately, even when empty).
- Encryption: Click the drop-down menu and select 256-bit AES encryption. This is military-grade encryption and highly recommended.
The moment you select the encryption level, a new dialog box will pop up demanding a password. Type a strong, memorable password, verify it, and click Choose. Warning: If you forget this password, there is absolutely no backdoor or recovery method. Your files will be lost forever.
- Leave all other settings (Format: Mac OS Extended (Journaled), Partitions: Single partition) at their defaults.
- Click Save.
Disk Utility will take a few moments to mathematically generate the encrypted vault. When it finishes, click Done.
How to Use the Encrypted Image
Using the image is incredibly straightforward.
- Navigate to your Desktop (or wherever you saved the file) and double-click the new
.dmgfile. - A secure password prompt will immediately appear. Type your password and click OK.
Once unlocked, the image will “mount” to your Mac exactly like a physical USB thumb drive. A new white drive icon will appear on your Desktop (or in the Finder sidebar). You can double-click this drive to open it, and then simply drag and drop your sensitive PDFs and photos into it.
When you are finished working with your sensitive files, you must “eject” the drive to lock the vault. Right-click the white drive icon and select Eject (or click the small eject symbol in the Finder sidebar). The vault is now locked, heavily encrypted, and safe to email or transfer to a portable flash drive.