Mount encrypted QNAP disk (crypto_LUKS) on an external computer

If one attempts to mount a QNAP disk encrypted with LUKS without unlocking it first, the following error will be shown:
mount: unknown filesystem type 'crypto_LUKS'

To mount and read data from a disk encrypted with crypto_LUKS (for example from a QNAP backup), use cryptsetup as per the below:

Install cryptsetup if not already installed:
sudo apt-get install cryptsetup

Unlock the disk (in this case /dev/sdb1 – adjust based on the device you wish to unlock). Select a good name for the unlocked disk. In this case we use “cryptodisk” but any name will work:

sudo cryptsetup luksOpen /dev/sdb1 cryptodisk
Enter passphrase for /dev/sdb1: 

The disk will be listed under /dev/mapper/. In this case /dev/mapper/cryptodisk:
sudo mount /dev/mapper/cryptodisk /home/user/mount/usb/

Now data can be accessed as normal via the mount point /home/user/mount/usb/

To unmount, do the following:
sudo umount /home/user/mount/usb

Finally lock the disk:
sudo cryptsetup luksClose cryptodisk

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