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How To Create an Encrypted Drive in a File Container
Posted by Bob Jonkman on 9th October 2017
Inspired by The Linux Experiment, I want to create an encrypted drive in a file container using only the command line.
Creating an encrypted file container
Create the container file. We’ll call it containerfile.img:
laptop:~/temp$ fallocate -l 250MB containerfile.img
laptop:~/temp$ ls -l
total 244148
-rw-rw-r-- 1 bjonkman bjonkman 250000000 Oct 8 22:45 containerfile.img
laptop:~/temp$
Create the encrypted LUKS volume. Note that creating volumes and file systems requires elevated privileges, so we use the sudo command:
laptop:~/temp$ sudo cryptsetup luksFormat containerfile.img
[sudo] password for bjonkman:
WARNING!
========
This will overwrite data on containerfile.img irrevocably.
Are you sure? (Type uppercase yes): YES
Enter passphrase:
Verify passphrase:
Command successful.
laptop:~/temp$
Of course, the passphrase doesn’t show on the screen, not even as asterisks. That would give a shouldersurfer an idea of how long the passphrase is. It is a long passphrase, right?
Open the encrypted LUKS volume, which we’ll call cryptvolume:
laptop:~/temp$ sudo cryptsetup luksOpen containerfile.img cryptvolume
Enter passphrase for containerfile.img:
laptop:~/temp$
Let’s see if the encrypted LUKS volume exists:
laptop:~/temp$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 465.8G 0 disk
├─sda1 8:1 0 243M 0 part
├─sda2 8:2 0 14G 0 part /
└─sda3 8:3 0 1K 0 part
loop4 7:4 0 238.4M 0 loop
└─cryptvolume 252:11 0 236.4M 0 crypt
laptop:~/temp$
Yay!
Now we create a filesystem inside the encrypted LUKS volume. We’ll give it the label cryptdrive:
laptop:~/temp$ sudo mkfs -L cryptdrive -t ext4 /dev/mapper/cryptvolume
mke2fs 1.42.13 (17-May-2015)
Creating filesystem with 253952 1k blocks and 63488 inodes
Filesystem UUID: 040765be-eddb-4ea6-b8d8-594b81233465
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729, 204801, 221185
Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
laptop:~/temp$
Create a mount point, which we’ll call mountpoint, then mount the encrypted drive:
laptop:~/temp$ mkdir mountpoint
laptop:~/temp$ sudo mount /dev/mapper/cryptvolume mountpoint
laptop:~/temp$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 465.8G 0 disk
├─sda1 8:1 0 243M 0 part
├─sda2 8:2 0 14G 0 part /
└─sda3 8:3 0 1K 0 part
loop4 7:4 0 238.4M 0 loop
└─cryptvolume 252:11 0 236.4M 0 crypt /home/bjonkman/temp/mountpoint
laptop:~/temp$ ls -l
total 244149
-rw-rw-r-- 1 bjonkman bjonkman 250000000 Oct 8 23:19 containerfile.img
drwxr-xr-x 3 root root 1024 Oct 8 23:14 mountpoint
laptop:~/temp$
Note that the encrypted file system still belongs to root:root because we used the sudo command.
Change file ownership to bjonkman:bjonkman so I can read/write to it without elevated permissions:
laptop:~/temp$ sudo chown bjonkman: mountpoint/
laptop:~/temp$ ls -l
total 244149
-rw-rw-r-- 1 bjonkman bjonkman 250000000 Oct 8 23:19 containerfile.img
drwxr-xr-x 3 bjonkman bjonkman 1024 Oct 8 23:14 mountpoint
laptop:~/temp$
Since an encrypted container file is probably secret, it shouldn’t be visible to groups or others, so remove those file permissions:
laptop:~/temp$ chmod go-rwx containerfile.img
laptop:~/temp$ ls -l
total 244149
-rw------- 1 bjonkman bjonkman 250000000 Oct 8 23:34 containerfile.img
drwxr-xr-x 3 bjonkman bjonkman 1024 Oct 8 23:14 mountpoint
laptop:~/temp$
Do some work in the encrypted drive:
laptop:~/temp$ echo "Hello World" > mountpoint/hello.txt
laptop:~/temp$ ls -l mountpoint/
total 13
-rw-rw-r-- 1 bjonkman bjonkman 12 Oct 8 23:53 hello.txt
drwx------ 2 root root 12288 Oct 8 23:14 lost+found
laptop:~/temp$
And finally, unmount the encrypted filesystem and close the encrypted volume:
laptop:~/temp$ sudo umount mountpoint/
laptop:~/temp$ sudo cryptsetup luksClose cryptvolume
laptop:~/temp$
Using an encrypted file container
Next time you want to do some work:
laptop:~/temp$ sudo cryptsetup luksOpen containerfile.img cryptvolume
Enter passphrase for containerfile.img:
laptop:~/temp$ sudo mount /dev/mapper/cryptvolume mountpoint
laptop:~/temp$ echo "Hello again" > mountpoint/again.txt
laptop:~/temp$ ls -l mountpoint/
total 14
-rw-rw-r-- 1 bjonkman bjonkman 12 Oct 9 00:12 again.txt
-rw-rw-r-- 1 bjonkman bjonkman 12 Oct 8 23:53 hello.txt
drwx------ 2 root root 12288 Oct 8 23:14 lost+found
laptop:~/temp$ sudo umount mountpoint/
laptop:~/temp$ sudo cryptsetup luksClose cryptvolume
laptop:~/temp$
Using an encrypted file container from the GUI
Once the encrypted file container has been created you can open it from the graphical file manager just by double-clicking:
Enter the passphrase to unlock the volume:
A file manager window for the encrypted volume opens:
Note that the mountpoint is /media/bjonkman/cryptdrive/, chosen by the Gnome Disk Mounter application that runs when you doubleclick the container:
laptop:~/temp$ lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 465.8G 0 disk
├─sda1 8:1 0 243M 0 part
├─sda2 8:2 0 14G 0 part /
└─sda3 8:3 0 1K 0 part
loop5 7:5 0 238.4M 1 loop
└─luks-54f8e41b-73bf-4adf-aa29-a147733c5202 252:11 0 236.4M 1 crypt /media/bjonkman/cryptdrive
laptop:~/temp$
Also, note that the encrypted drive is mounted read-only:
laptop:~/temp$ mount | grep cryptdrive
/dev/mapper/luks-54f8e41b-73bf-4adf-aa29-a147733c5202 on /media/bjonkman/cryptdrive type ext4 (ro,nosuid,nodev,relatime,data=ordered,uhelper=udisks2)
laptop:~/temp$
Gnome Disk Mounter can be launched from the command line with a --writeable or -w parameter:
Happily, this all works without elevated privileges; no sudo required. I don’t know how to open an encrypted file container using only command line tools without using sudo, nor how to launch Gnome Disk Manager in writeable mode just by doubleclicking — if you know, leave a comment or send me e-mail!
TL;DR:
fallocate -l 250MB containerfile.img
sudo cryptsetup luksFormat containerfile.img
sudo cryptsetup luksOpen containerfile.img cryptvolume
sudo mkfs -L cryptdrive -t ext4 /dev/mapper/cryptvolume
mkdir mountpoint
sudo mount /dev/mapper/cryptvolume mountpoint
sudo chown bjonkman: mountpoint/
chmod go-rwx containerfile.img
(do some work)
sudo umount mountpoint/
sudo cryptsetup luksClose cryptvolume
-----
sudo cryptsetup luksOpen containerfile.img cryptvolume
sudo mount /dev/mapper/cryptvolume mountpoint
(do some work)
sudo umount mountpoint/
sudo cryptsetup luksClose cryptvolume
Tags: Crypto, encrypted volume, encryption, LUKS
Posted in GNU/Linux | 1 Comment »
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