#general help
cryptsetup luksFormat --help

#format
cryptsetup luksFormat /dev/sdc1

#open
cryptsetup luksOpen /dev/sdc1 mywd

#see dev mapper devices
ls -lh /dev/mapper/

#zero it out (could take a long time - use pv to monitor)
pv -tpreb /dev/zero | dd of=/dev/mapper/mywd bs=512M

#make partition
mkfs -t ext2 /dev/mapper/mywd

#mount
mount -t auto /dev/mapper/mywd /mnt/mywd

#see status
cryptsetup -v status mywd


#add a keyfile (will aask for exisiting pass)
cryptsetup luksAddKey /dev/sdc1 /etc/keys/sdc1_key

#then it's possible to
cryptsetup --key-file=/etc/keys/sdc1_key luksOpen /dev/sdc1 mywd

#finally to kill the old passphrase
cryptsetup --key-file=/etc/keys/sdc1_key luksKillSlot /dev/sdc1 0

#to close 
cryptsetup luksClose mywd