Unlock your FileVault-encrypted boot drive using Disk Utility on macOS Mojave
In the event that you need to unlock an unbootable FileVault-encrypted boot drive on macOS Mojave, it’s possible to do so using Disk Utility and the password to a FileVault-enabled account on the drive.
For more details, see below the jump.
To unlock an encrypted boot drive, please use the procedure shown below:
Note: For this example, I’m using Recovery HD‘s Disk Utility though you can also use Disk Utility from a regular boot drive.
1. Open Disk Utility.
2. Select the locked encrypted drive.
3. Click the Mount button.
Alternatively, you can select the Mount command under the File menu.
4. In the password blank which appears, enter the password to a FileVault-enabled account on the drive.
5. If the authentication is accepted, the drive should unlock and mount.
Note: You will not be able to decrypt from Disk Utility on macOS Mojave. If decryption is necessary, you will need to use the command line method documented at the link below:
One item of interest is that on macOS High Sierra, it is possible to unlock a FileVault-encrypted boot drive with Disk Utility using one of the following authentication credentials:
- The password to a FileVault-enabled account on the drive
- A personal recovery key
As of macOS Mojave 10.14.2, the ability to use a personal recovery key with Disk Utility to unlock an encrypted drive has apparently been removed.
Der Flounder 
Great site! Have you ever seen a case where on step 4, it won’t allow you to type in the password field? It’s like the field is totally disabled. I’m guessing perhaps that means the user account has become corrupted somehow, but don’t know for sure.
Hi Mark, i’m experiencing exactly the same on a MacBook Pro with Mojave currently. The machine does not boot at all, and i’m not able to enter anything in the password field that pops up in recovery. I tried all related passwords, even in the diskutil tool via commandline, but no way of unlockng the drive. Do you have any hints for me? I need to recover some data that exists in the locked partition 😦
Unfortunately I was never able to recover the data. I tried many of the same things you mention above, to no avail. My best understanding of what happened is that reformatting to APFS corrupted the user account and there was no way to recover it. I eventually just wiped it, sold it, and started over (this time with iCloud auto backup enabled).
Thanks for the feedback! I will make one try with Apple Support and see whether they can help me. Otherwise i believe the data is gone 😦