sudo apt-get install qemu-utils
modprobe nbd
qemu-nbd -c /dev/nbd0 <vdi-file>
mount /dev/nbd0p1 /mnt
umount /mnt
qemu-nbd -d /dev/nbd0
modprobe nbd
qemu-nbd -c /dev/nbd0 <vdi-file>
mount /dev/nbd0p1 /mnt
umount /mnt
qemu-nbd -d /dev/nbd0
https://www.howtogeek.com/427982/how-to-encrypt-and-decrypt-files-with-gpg-on-linux/