ctmg is an encrypted container manager for Linux using
cryptsetup and various standard file system utilities. Containers have the extension
.ct and are mounted at a directory of the same name, but without the extension. Very simple to understand, and very simple to implement;
ctmg is a simple bash script.
Usage: ctmg [ new | delete | open | close | list ] [arguments...] ctmg new container_path container_size[units_suffix] ctmg delete container_path ctmg open container_path ctmg close container_path ctmg list
ctmg with no arguments will call
list if there are any containers open, and otherwise show the usage screen. Calling
ctmg with a filename argument will call
open if it is not already open and otherwise will call
Create a 100MiB encrypted container called "example"
zx2c4@thinkpad ~ $ ctmg new example 100MiB [#] truncate -s 100MiB /home/zx2c4/example.ct [#] cryptsetup --cipher aes-xts-plain64 --key-size 512 --hash sha512 --iter-time 5000 --batch-mode luksFormat /home/zx2c4/example.ct Enter passphrase: [#] chown 1000:1000 /home/zx2c4/example.ct [#] cryptsetup luksOpen /home/zx2c4/example.ct ct_example Enter passphrase for /home/zx2c4/example.ct: [#] mkfs.ext4 -q -E root_owner=1000:1000 /dev/mapper/ct_example [+] Created new encrypted container at /home/zx2c4/example.ct [#] cryptsetup luksClose ct_example
Open a container, add a file, and then close it
zx2c4@thinkpad ~ $ ctmg open example [#] cryptsetup luksOpen /home/zx2c4/example.ct ct_example Enter passphrase for /home/zx2c4/example.ct: [#] mkdir -p /home/zx2c4/example [#] mount /dev/mapper/ct_example /home/zx2c4/example [+] Opened /home/zx2c4/example.ct at /home/zx2c4/example zx2c4@thinkpad ~ $ echo "super secret" > example/mysecretfile.txt zx2c4@thinkpad ~ $ ctmg close example [#] umount /home/zx2c4/example [#] cryptsetup luksClose ct_example [#] rmdir /home/zx2c4/example [+] Closed /home/zx2c4/example.ct
# make install
Or, use the package from your distribution:
# emerge ctmg
Report any bugs to firstname.lastname@example.org.
This runs as root and auto-
sudos itself to achieve that. As such, you shouldn't run this on paths you don't trust or paths that could be controlled by malicious users.
cryptsetup and the LUKS infrastructure, it uses the Linux block device encryption APIs. The state of the art in block device encryption, as of writing, is XTS mode, which is what
ctmg uses. But do note that this does not guarantee, entirely, the integrity of data, just the secrecy. As such, if a malicious user is able to modify the encrypted content, it is possible this could result in differing decrypted content without you noticing. So,
ctmg is useful for keeping things secret, but not for guaranteeing the authenticity of the data. If your laptop gets stolen, sleep safely knowing that your
ctmg-secured data is safe, but if an attacker is actively modifying the
.ct file while you're using it in one way or another, you've got trouble.
In order to conserve space,
truncate to make sparse files. This means that the file grows as it's used. An attacker can therefore see how much of the container is utilized. If you care about this, it's easy enough to replace the single call to
truncate with a single call to
dd if=/dev/urandom to make a completely full file containing only random data.