Insert the encrypted device in your Mac. It will tell you it can’t use it and would invite you to initialize it. Just click “Ignore”. Run the disk utility to identify what disk is your encrypted device (probably it will be “disk2”).

Then open a terminal and run the following:

$ sudo VBoxManage internalcommands createrawvmdk -filename mydevice.vmdk -rawdisk /dev/disk2

Replace “disk2” by the actual disk for you.

WARNING Don’t get this wrong or you can corrupt your Mac’s hard drive!

In VirtualBox, select your VM and click “Settings”. Then click “Storage” and “Controller: SATA”. Then click on the “plus” icon next to “Controller: SATA” (either optical drive or hard disk). Then click “Choose existing disk”. Click the “Add” button and locate the “mydevice.vmdk” file. Ensure it is selected and click “Choose”. Then start your Ubuntu VM and `lsblk` should see the new device now.

For some reason, Nautilus doesn’t show it, so I had to set it up manually:

$ sudo lsblk  # Locate your encrypted partition
$ sudo cryptsetup open /dev/sdb1 mydevice  # Replace sdb1 by what you identified in lsblk
$ sudo mount /dev/mapper/mydevice /mnt