The userspace partition leaves no space for the key, so it has to be shrunk
Similar to OnePlus One with CM11: TeamWin/Team-Win-Recovery-Project#291
data_dev_size=$(cat /sys/class/block/sda13/size)
new_fs_size=$(( (($data_dev_size/2)-16) ))
umount /data
mkfs.ext4 /dev/block/sda13 $new_fs_size