Plugging in an encrypted USB drive should be simple: macOS asks for the password, unlocks the volume, and shows it in Finder. When that does not happen, the problem can feel alarming—especially if the drive contains work files, photos, backups, or sensitive documents. The good news is that many “USB drive decryption not working on Mac” issues are caused by format incompatibility, a damaged file system, faulty connections, or macOS security prompts that are easy to miss.
TLDR: First, confirm what type of encryption the USB drive uses, because Macs can unlock APFS and Mac OS Extended encrypted drives but do not natively decrypt BitLocker drives. Try a different port, cable, user account, and Mac, then check the drive in Disk Utility. If the volume appears but will not mount, run First Aid and use Terminal commands such as diskutil list to identify it. Avoid reformatting unless you have recovered or backed up the data, because erasing the drive permanently removes the encrypted contents.
1. Confirm the Encryption Type
Before troubleshooting deeply, identify how the USB drive was encrypted. This matters because not all encryption systems are supported by macOS.
- APFS Encrypted: Common on newer Macs. macOS can unlock it if you know the password.
- Mac OS Extended Journaled Encrypted: Older Mac format, also supported by macOS.
- BitLocker: Windows encryption. macOS cannot decrypt BitLocker drives without third-party software or a Windows machine.
- Hardware encrypted USB drives: Some drives require a keypad, manufacturer app, or special unlock process.
If the USB was encrypted on a Windows PC with BitLocker, your Mac may show the drive as unreadable, ask to initialize it, or simply fail to mount it. In that case, do not click “Initialize” if you need the files. Use a Windows computer to unlock it or install reputable BitLocker reader software for Mac.
2. Check the Simple Hardware Issues First
It sounds basic, but connection problems are a frequent reason an encrypted drive will not prompt for a password. Encryption adds another layer of complexity, so a weak connection can make macOS detect the device but fail to mount the encrypted volume.
Try these quick checks:
- Unplug the USB drive and reconnect it firmly.
- Use another USB port, preferably directly on the Mac instead of through a hub.
- If using a USB C adapter, test a different adapter.
- Try another cable if the drive is external and cable based.
- Restart the Mac and reconnect the drive after logging in.
- Test the drive on another Mac or the original computer used to encrypt it.
If the drive works on another computer, your Mac may have a software, permission, or compatibility issue. If it fails everywhere, the drive or its file system may be damaged.
3. Look for the Drive in Disk Utility
Finder may not show a locked or damaged encrypted drive, but Disk Utility often will. Open Applications > Utilities > Disk Utility. Then choose View > Show All Devices. This is important because macOS may hide containers or volumes by default.
Look in the sidebar for your USB device. You may see the physical drive, an APFS container, and one or more volumes beneath it. Select the encrypted volume and check whether there is a Mount or Unlock option. If macOS asks for the password, enter it carefully. Passwords for encrypted drives are case sensitive, and keyboard layout differences can cause mistakes if the drive was encrypted on another system.
If you see the drive but it is grayed out, that is still useful. It means macOS detects the hardware, but the volume may be locked, corrupted, or formatted in a way the Mac cannot read.
4. Run First Aid on the Drive
If the encrypted volume appears in Disk Utility but will not unlock or mount properly, use First Aid. This tool checks and repairs common file system errors.
- Open Disk Utility.
- Select the encrypted volume, not just the physical device.
- Click First Aid.
- Confirm and wait for the scan to finish.
- If First Aid reports repairs, try mounting or unlocking the drive again.
Run First Aid on the volume first, then the container, then the physical disk if needed. If First Aid fails, write down the error message. Phrases like “invalid node structure,” “could not mount,” or “APFS object map is invalid” may indicate file system damage that requires professional recovery tools or services.
5. Use Terminal to Identify and Unlock the Volume
When the graphical tools are not enough, Terminal can reveal what macOS actually sees. Open Applications > Utilities > Terminal and type:
diskutil list
This command lists connected disks and volumes. Find your USB drive by size, name, or format. It may appear as something like /dev/disk4 or /dev/disk4s2.
For APFS encrypted volumes, you can also use:
diskutil apfs list
This shows APFS containers and encrypted volumes. If the volume is locked, macOS may show its encryption status. You can attempt to unlock an APFS volume with:
diskutil apfs unlockVolume diskXsY
Replace diskXsY with the correct identifier, such as disk4s2. Terminal should ask for the password. Be careful: using the wrong erase or format command can destroy the data. If you are unsure which disk is which, stop and verify before continuing.
6. Check Password, Keychain, and Keyboard Issues
Sometimes decryption fails because the password entered is not the password macOS receives. This can happen if your keyboard layout changed, if Caps Lock is on, or if special characters are in different places on another keyboard.
Try typing the password into a plain text field first, such as TextEdit, to confirm the characters appear as expected. If you previously saved the password to Keychain, open Keychain Access and search for the drive name. You may find a saved disk password there, depending on your earlier settings.
Also consider whether the drive was encrypted by another user account. Some encrypted volumes are tied to specific credentials, certificates, recovery keys, or device management profiles, especially in business environments.
7. Update macOS and Try Safe Mode
Older macOS versions may have trouble with newer APFS implementations, especially if the drive was encrypted on a more recent Mac. Go to System Settings > General > Software Update and install available updates.
You can also try booting into Safe Mode, which loads only essential system components and clears certain caches. On Apple silicon Macs, shut down, hold the power button until startup options appear, select your disk, hold Shift, and choose Continue in Safe Mode. On Intel Macs, restart and hold Shift during startup. Once in Safe Mode, connect the USB drive and try unlocking it again.
8. If macOS Says the Disk Is Unreadable
If you see a message saying the disk is unreadable and offering Initialize, be cautious. “Initialize” opens Disk Utility and often leads users toward erasing or reformatting the drive. That may make the USB usable again, but it will not fix access to your existing encrypted data.
If the files matter, try the drive on the computer where it was encrypted. If it is BitLocker, use Windows. If it is a Mac encrypted drive, try another Mac with a similar or newer macOS version. For physically failing drives—clicking sounds, repeated disconnects, excessive heat, or very slow detection—stop repeated attempts and consider professional data recovery.
9. Reformat Only as a Last Resort
If you no longer need the data and simply want the USB drive to work again, you can erase it in Disk Utility. Select the physical drive, click Erase, and choose a format. Use APFS for Mac only storage, Mac OS Extended for older Mac compatibility, or exFAT for sharing between Mac and Windows. If you want encryption, choose an encrypted format and store the password somewhere safe.
Important: reformatting removes the encrypted volume and its contents. It is not a repair step for data you still need.
Final Thoughts
USB drive decryption problems on Mac usually come down to one of four causes: incompatible encryption, connection trouble, file system damage, or password issues. Start with the least risky checks, then move to Disk Utility and Terminal only when needed. Most importantly, never erase, initialize, or reformat an encrypted USB drive until you are certain the data is backed up or no longer needed. With a careful approach, you can often restore access—or at least avoid making recovery harder.
