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How to decrypt the Filevault encrypted volume using Recovery HD ?

There might be a time where you want decrypt the FileVault encrypted mac, but you are facing issues in logging into Mac to perform decryption using system preferences. In such cases the following steps will help you in decrypting the disk using Recovery HD.
  1. Reboot the Mac, Go to recovery HD partition of the system. (To start your computer from Recovery, restart your Mac and hold down the Command and R keys at startup.)
  2. Open Terminal application from Utilities -> Application. 
  3. First will need to identify the Logical Volume UUID of the encrypted drive using the diskutil corestorage list command:
          diskutil corestorage list 

      4.  Once you have the UUID of the logical volume as shown in above picture, you can then either             unlock or decrypt the encrypted volume using the following commands.

      a) Using the password of an authorised account or the recovery key ( Provided by the                                FileVault at the time of enabling it) on the command line
           To unlock: diskutil corestorage unlockVolume UUID –stdinpassphrase  

           The -stdinpassphrase flag will cause the command to prompt you for the password/passphrase
          of an account that’s authorised to unlock the encryption or the recovery key for the system. If              successful, the drive will unlock and mount.

      5.   Once we have unlocked the disk, we can now decrypt the volume.
            To decrypt: diskutil corestorage revert UUID –stdinpassphrase  

          You’ll be prompted for the password/passphrase of an account that’s authorised to unlock the              encryption or the recovery key. Once provided, decryption of the encrypted volume will                      begin. To track its progress, you can use the diskutil corestorage list command. Once the drive            has been completely decrypted, it will no longer be listed as a CoreStorage volume by diskutil            corestorage list. In Disk Utility, it will appear as a normal hard drive.  

      6.   Reboot the mac , It is now no longer encrypted with FileVault.



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