The option names changed since this nice howto has been posted, and it doesn't seem to be documented, so here's how to do it in 0.8:
zpool set feature@encryption=enabled tank head -c 32 /dev/random >/root/key zfs create -o encryption=aes-256-gcm -o keyformat=raw -o keylocation=file:///root/key tank/encrypted
Edit 2019-11-18: The above is not enough to have ZFS auto-mount the filesystem after reboot, at least not on CentOS 8. Here's the systemd unit file which makes it work (don't forget to systemctl enable zfs-load-key.service):
[root@db ~]# cat /etc/systemd/system/zfs-load-key.service [Unit] Description=Load ZFS keys Documentation=man:zfs(8) DefaultDependencies=no After=systemd-udev-settle.service After=zfs-import.target After=systemd-remount-fs.service Before=zfs-mount.service [Service] Type=oneshot RemainAfterExit=yes ExecStart=/sbin/zfs load-key -a [Install] WantedBy=zfs.target