Encrypted Filesystems

Revision as of 08:31, 30 October 2015

Introduction

You might be asking yourself what is an encrypted filesystem good for? There are many answers, and a few might be storage of: RSA private keys, password lists, tripwire checksums, Mafia book keeping, plans for world domination, or whatever you can think of! When the men in black suits come to get your private info, they will have a very difficult job. You will be using the following commands in this exercises: dd, df, gbde, mdconfig, and mount.

First thing is to man the above commands, and take a look at the "Encrypted Filesystem" example in the FreeBSD Handbook. This is an extension of the example found in the handbook.

There are two programs used to encrypt file systems, which are gdbe and geli.

Swap encryption through /etc/fstab

Swap encryption is useful to keep passwords and other confidential information out of view. To encrypt swap partitions the geli program is useful. Open the file /etc/fstab and add .eli at the end of the swap device, under the colum #Device. For example:

#Device			Mountpoint		Fstype		Options		Dump		Pass#
/dev/ada0p1.eli		none			swap		sw		0		0

The above and a reboot are sufficient to encrypt swap.

The gbde program can also be used to encrypt swap space. It uses the .bde suffix in the /etc/fstab file. Please read it's manpage for details, and read below.

Configuration

Load GEOM_BDE support into the kernel. (Note: if you wish, you may also add GEOM_BDE support to the kernel statically and recompile it - use options GEOM_BDE.)

# kldload geom_bde

If you chose to use dynamic GEOM kernel support instead of recompiling it into the kernel, you may also want to make sure it's autoloaded at boot time from here on out:

# echo geom_bde_load="YES" >> /boot/loader.conf

Create a few directories. One for lock files, and the other for a mount point.

# mkdir /private
# mkdir /etc/gbde

Create an empty image file of 1000Mb.

masta# touch /usr/local/cryptfs.img
masta# dd if=/dev/zero of=/usr/local/cryptfs.img bs=1024k count=1000

Create a virtual device that points the empty file.

# mdconfig -a -t vnode -u 9 -f /usr/local/cryptfs.img

Invoke the gbde program on the new virtual device. This will ask for a passphrase twice, and open an editor.

# gbde init /dev/md9 -i -L /etc/gbde/md9

In the Editor, alter the "sector_size" line, and exit.

g/sector_size = 512/s//sector_size = 2048/g

NOTE: You should have a /dev/md9.bde device-node.

Invoke the gbde program to attach the image file to the kernel.

# gbde attach /dev/md9 -l /etc/gbde/md9

NOTE: You will be prompted for the passphrase.

Format the attached image with UFS2:

# newfs -U -O2 /dev/md9.bde

Now mount the md9.bde filesystem to the mount-point we created earlier.

# mount /dev/md9.bde /private

Check to make sure everthing worked.

# df -h

NOTE: this article was reproduced and minorly reformatted from http://www.ezunix.org/modules.php?op=modload&name=Sections&file=index&req=viewarticle&artid=67&page=1 and has not been tested for accuracy. Information on updates to encrypt swap are based on Network Administration with FreeBSD7.

You can automount encrypted partitions with 2 rc.conf variables:

gbde_autoattach_all="YES"
gbde_devices="encrypteddrivedeveicename"