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How to encrypt an external drive or card in macOS

Looking to encrypt removable storage on macOS, but can’t figure out how? Jack Wallen shows you the way to make this work.

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Image: iStockphoto/nicescene

In this day and age, encryption has become a necessary part of doing business for some. It might not be the most efficient way of working, but the added security gained by making use of encryption technologies more than makes up for having to take a few extra steps. Because sensitive information is not only the domain of business, this holds true for home users as well.

Depending on your platform, you might have to install third-party software to encrypt externally-attached drives, such as USB drives and memory cards. With macOS, however, you don’t. Everything you need to encrypt those drives is built right into the platform.

I want to walk you through the steps of encrypting an SD card using only the included software on a MacBook Pro, running macOS 10.15.5.

SEE: Flash storage: A guide for IT pros (TechRepublic Premium)

What you’ll need

As you probably expect, you’ll need an Apple machine to make this work. You’ll also need an SD card and a card reader or a USB drive.

How to enable encryption

Chances are probably good that encryption is already enabled on your macOS device. If not, you can make it so by opening System Preferences and navigating to Security & Privacy. Once there, click on the FileVault tab. If FileVault is enabled, Turn Off FileVault will be grayed out (Figure A).

Figure A

Encryption is already enabled.

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Encryption is already enabled.

If FileVault isn’t enabled, make sure your machine is plugged into a power outlet, click Turn On FileVault, type your user password, and wait for the process to complete. During this process you’ll be asked if you want to use iCloud to decrypt the drive. This is offered in case you forget your encryption password. 

The one caveat to using iCloud for this purpose is that your machine must have an internet connection in order for it to work. So your best bet is to remember your encryption password and save the 20-digit recovery code as that recovery code can also be used decrypt your drive.

How to encrypt a memory card

Let’s encrypt an SD memory card. Before we dive into this, understand that the process will erase everything on the card. So make sure to copy all of the files from the card to local storage. You can then copy everything back, once the drive is encrypted.

To encrypt the card, insert it into your reader and attach the reader to the machine. Once the card is recognized, open the Disk Utility app (found in Launchpad). You should see the card listed in the left pane. However, that’s not the view you want. In the top-left of the Disk Utility window, click the View drop-down and select Show All Devices (Figure B).

Figure B

Viewing all devices in Disk Utility.

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Viewing all devices in Disk Utility.

You should now see the actual name of the card listed (such as Generic – Multi-Card Media). Select that entry and click Erase from the top toolbar. In the resulting window, give the card a new name (or the same name it had), select Mac OS Extended from the Format drop-down, and select GUID Partition Map from the Scheme drop-down. Click Erase to format the card (Figure C).

Figure C

Formatting an SD card in macOS.

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Formatting an SD card in macOS.

Once the formatting is finished, click Done.

How to encrypt the newly-formatted card

It’s now time to encrypt the newly-formatted card. Open Finder and right-click (or double-finger tap) the SD card listing in the left pane. From the menu, select the Encrypt entry (Figure D).

Figure D

Encrypting an SD card in macOS.

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Encrypting an SD card in macOS.

You will be prompted to type and verify an encryption password, and add a (required) password hint (Figure E).

Figure E

Adding a password and hint for the SD card encryption in macOS.

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Adding a password and hint for the SD card encryption in macOS.

Once you’ve filled out the necessary information, click Encrypt Disk. When this process completes, you can then add the files back to the disk, and eject it from the machine. Your SD card is now protected behind a layer of encryption. The only way anyone can read that disk is by entering the encryption password you created.

Congratulations, the data on that removable device is now protected. 

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