# cryptsetup luksAddKey --pbkdf pbkdf2
# then remove the new format keys with cryptsetup luksRemoveKey
# then cryptsetup convert DEV --type luks1, then readd old keys and remove temp.
# cryptsetup luksAddKey --pbkdf pbkdf2
# then remove the new format keys with cryptsetup luksRemoveKey
# then cryptsetup convert DEV --type luks1, then readd old keys and remove temp.