Sunday, June 5, 2011

[Security] Protect your personal data (gnu/Linux users)

1) What?

This blog presents a secure way to protect your personal data. The solution is designed to run on "Unix like" operating systems, e.g.: gnu/Linux, Mac OSX.
If you are looking for a solution to secure your professional data, please referrer to your corporate security policy.

2) Problem

You are still wondering how to keep your personal data secure. What about?
1) A USB key with plain text files
- the key is stolen, all your data are compromised.
2) A Google Spreadsheet
- if Google is hacked
- when you are off line
3) An encrypted zip file
- if your file is stolen, it might be opened using a brutal force attack
- when you are opening a text file, it is temporally copied to your system temp directory
4) A third party tool
- why will you pay for a closed source tool? This is a matter of confidence
5) An encrypted partition on your hard drive
- yeah, smart idea
- the data can only be accessed from your laptop, and you might need your personal password when you are far from your personal computer
6) An encrypted file partition stored on an USB Key
- Definitely YES!

3) Solution Set-up

You will find similar solutions on the Internet. This one worked pretty well on Ubuntu 10.

I recommend that you run all these steps log in as the root user.

Step 1:
Create a 256MB disk file (zero-filled) called file01. I choose to create it under my home directory:
dd if=/dev/zero of=/home/olivier/virtualfs/file01 bs=1024 count=262144 
Then you might want to change the file owner, e.g.:
chmod olivier.olivier /home/olivier/virtualfs/file01

Step 2:
Get the first free loopback devices:
losetup -f
The command losetup -a lists all the loopback devices already in use.

Step 3:
Attach the first loopback device to your disk file:
losetup /dev/loop0 /home/olivier/virtualfs/file01

Step 4:
Crypt the disk:
cryptsetup luksFormat -c aes -h sha256 /dev/loop0
You will be ask for a pass phrase. Choose it carefully. It must not be equal to another of your passwords. Remember the Play Station Network hacking. Re using several times the same password is highly insecure.

Step 5:
Mount the disk in the system:
cryptsetup luksOpen /dev/loop0 secure01

Step 6:
Format the file system, choose your flavor:
mkfs.ext3 /dev/mapper/secure01

Step 7:
Mount the file system:
mk /media/secure01
mount -t ext3 /dev/mapper/secure01 /media/secure01
chmod 777 /media/secure01

umount /media/secure01
cryptsetup luksClose secure01
losetup -d /dev/loop0

4) Automate the Solution

I wrote these two scripts in order to easily mount/unmount the file disk.
This is a generic script that enable to handle multiple file disks without bothering the mounting order: the first loop device is auto detect and the unmount is based on the path.
If the script is not executed by the root user, it is ran again using a sudo command (assuming the running user is in the sudoers list).

if [ "`whoami`" != "root" ]; then
  sudo $0

# check if already mounted
if [ -n "`losetup -a | grep $DEVICE_FS_PATH`" ]; then
  echo "Device already mounted."

DEVICE=`losetup -f`
cryptsetup luksOpen $DEVICE secure01
mount -t ext3 /dev/mapper/secure01 /media/secure01

if [ "`whoami`" != "root" ]; then
  sudo $0

DEVICE=`losetup -a | grep $DEVICE_FS_PATH | awk -F":" '{print $1}'`

umount /media/secure01
cryptsetup luksClose secure01
losetup -d $DEVICE

You might want to copy the file to a usb key and keep a backup copy on your laptop. If you lost the key, the data will not be compromised. The robber will find a key with an unknown file system, Windows will probably suggest to format it in FAT-32...


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