Setup access to encrypted device. If necessary, passphrase is requested interactively. Option device configures specific grub device (see Naming convention); option -u uuid configures device with specified uuid; option -a configures all detected encrypted devices; option -b configures all geli containers that have boot flag set.
GRUB suports devices encrypted using LUKS and geli. Note that necessary modules (luks and geli) have to be loaded manually before this command can be used.