# open encrypted partition /dev/sdb1 (reachable at /dev/mapper/backup)
cryptsetup open --type luks /dev/sdb1 backup

# open encrypted partition /dev/sdb1 using a keyfile (reachable at /dev/mapper/hdd)
cryptsetup open --type luks --key-file hdd.key /dev/sdb1 hdd

# close luks container at /dev/mapper/hdd
cryptsetup close hdd

# create encrypted disk
cryptsetup luksFormat --type luks2 /dev/sdd