In this book, I will explain how to encrypt your partitions using Linux Unified Key Setup-on-disk-format (LUKS) on your Linux based computer or laptop.
- 1 Linux encryption methods
- 2 Install cryptsetup utility
- 3 Configure LUKS partition
- 4 Format LUKS partition
- 5 How do I unmount and secure data?
- 6 How do I mount or remount encrypted partition?
- 7 Can I run fsck on LUKS based partition / LVM volume?
- 8 How do I change LUKS passphrase (password) for encrypted partition?
Linux encryption methods
There are two methods to encrypt your data:
Filesystem stacked level encryption
- eCryptfs - It is a cryptographic stacked Linux filesystem. eCryptfs stores cryptographic metadata in the header of each file written, so that encrypted files can be copied between hosts; the file will be decrypted with the proper key in the Linux kernel keyring. This solution is widely used, as the basis for Ubuntu's Encrypted Home Directory, natively within Google's ChromeOS, and transparently embedded in several network attached storage (NAS) devices.
- EncFS -It provides an encrypted filesystem in user-space. It runs without any special permissions and uses the FUSE library and Linux kernel module to provide the filesystem interface. You can find links to source and binary releases below. EncFS is open source software, licensed under the GPL.
Block device level encryption
- Loop-AES - Fast and transparent file system and swap encryption package for linux. No source code changes to linux kernel. Works with 3.x, 2.6, 2.4, 2.2 and 2.0 kernels.
- Truecrypt - It is free open-source disk encryption software for Windows 7/Vista/XP, Mac OS X and Linux. (Deprecated)
- dm-crypt+LUKS - dm-crypt is a transparent disk encryption subsystem in Linux kernel v2.6+ and later and DragonFly BSD. It can encrypt whole disks, removable media, partitions, software RAID volumes, logical volumes, and files.
Install cryptsetup utility
You need to install the following package. It contains cryptsetup, a utility for setting up encrypted filesystems using Device Mapper and the dm-crypt target. Debian / Ubuntu Linux user type the following apt-get command:
# apt-get install cryptsetup
Reading package lists... Done Building dependency tree Reading state information... Done The following extra packages will be installed: cryptsetup-bin libcryptsetup4 Suggested packages: busybox The following NEW packages will be installed: cryptsetup cryptsetup-bin libcryptsetup4 0 upgraded, 3 newly installed, 0 to remove and 7 not upgraded. Need to get 168 kB of archives. After this operation, 669 kB of additional disk space will be used. Do you want to continue [Y/n]? y Get:1 http://ap-northeast-1.ec2.archive.ubuntu.com/ubuntu/ precise/main libcryptsetup4 amd64 2:1.4.1-2ubuntu4 [55.8 kB] Get:2 http://ap-northeast-1.ec2.archive.ubuntu.com/ubuntu/ precise/main cryptsetup-bin amd64 2:1.4.1-2ubuntu4 [32.2 kB] Get:3 http://ap-northeast-1.ec2.archive.ubuntu.com/ubuntu/ precise/main cryptsetup amd64 2:1.4.1-2ubuntu4 [80.0 kB] Fetched 168 kB in 0s (268 kB/s) Preconfiguring packages ... Selecting previously unselected package libcryptsetup4. (Reading database ... 25374 files and directories currently installed.) Unpacking libcryptsetup4 (from .../libcryptsetup4_2%3a1.4.1-2ubuntu4_amd64.deb) ... Selecting previously unselected package cryptsetup-bin. Unpacking cryptsetup-bin (from .../cryptsetup-bin_2%3a1.4.1-2ubuntu4_amd64.deb) ... Selecting previously unselected package cryptsetup. Unpacking cryptsetup (from .../cryptsetup_2%3a1.4.1-2ubuntu4_amd64.deb) ... Processing triggers for man-db ... Processing triggers for ureadahead ... Setting up libcryptsetup4 (2:1.4.1-2ubuntu4) ... Setting up cryptsetup-bin (2:1.4.1-2ubuntu4) ... Setting up cryptsetup (2:1.4.1-2ubuntu4) ... update-initramfs: deferring update (trigger activated) Processing triggers for libc-bin ... ldconfig deferred processing now taking place Processing triggers for initramfs-tools ... update-initramfs: Generating /boot/initrd.img-3.2.0-31-virtual
RHEL / CentOS / Fedora Linux user type the following yum command:
# yum install cryptsetup-luks
Configure LUKS partition
WARNING! The following command will remove all data on the partition that you are encrypting. You WILL lose all your information! So make sure you backup your data to an external source such as NAS or hard disk before typing any one of the following command.
In this example, I'll use partition called /dev/xvdc, and our first task will be to overwrite that partition 3 times with random data, that's enough to protect you against forensic investigation. It took me nearly 30 minutes for 20 GB partition to be overwritten 3 times.
# shred --verbose --random-source=/dev/urandom --iterations=3 /dev/xvdc
Next, I'm going to encrypt /dev/xvdc. Type the following command:
# cryptsetup --verbose --cipher aes-xts-plain64 --key-size 512 --hash sha512 --iter-time 5000 --use-urandom luksFormat /dev/xvdc
WARNING! ======== This will overwrite data on /dev/xvdc irrevocably. Are you sure? (Type uppercase yes): YES Enter LUKS passphrase: Verify passphrase: Command successful.
This command initializes the volume, and sets an initial key or passphrase. Please note that the passphrase is not recoverable so do not forget it.Type the following command create a mapping:
# cryptsetup luksOpen /dev/xvdc backup2
Enter passphrase for /dev/xvdc:
You can see a mapping name /dev/mapper/backup2 after successful verification of the supplied key material which was created with luksFormat command extension:
# ls -l /dev/mapper/backup2
lrwxrwxrwx 1 root root 7 Oct 19 19:37 /dev/mapper/backup2 -> ../dm-0
You can use the following command to see the status for the mapping:
# cryptsetup -v status backup2
/dev/mapper/backup2 is active. type: LUKS1 cipher: aes-cbc-essiv:sha256 keysize: 256 bits device: /dev/xvdc offset: 4096 sectors size: 419426304 sectors mode: read/write Command successful.
You can dump LUKS headers using the following command:
# cryptsetup luksDump /dev/xvdc
Format LUKS partition
First, you need to write zeros to /dev/mapper/backup2 encrypted device. This will allocate block data with zeros. This ensures that outside world will see this as random data i.e. it protect against disclosure of usage patterns:
# dd if=/dev/zero of=/dev/mapper/backup2
The dd command may take many hours to complete. I suggest that you use pv command to monitor the progress:
# pv -tpreb /dev/zero | dd of=/dev/mapper/backup2 bs=128M
To create a filesystem i.e. format filesystem, enter:
# mkfs.ext4 /dev/mapper/backup2
To mount the new filesystem at /backup2, enter:
# mkdir /backup2 # mount /dev/mapper/backup2 /backup2 # df -H # cd /backup2 # ls -l
How do I unmount and secure data?
Type the following commands:
# umount /backup2 # cryptsetup luksClose backup2
How do I mount or remount encrypted partition?
Type the following command:
# cryptsetup luksOpen /dev/xvdc backup2 # mount /dev/mapper/backup2 /backup2 # df -H # mount
See shell script wrapper that opens LUKS partition and sets up a mapping for nas devices.
Can I run fsck on LUKS based partition / LVM volume?
Yes, you can use the fsck command on LUKS based systems:
# umount /backup2 # fsck -vy /dev/mapper/backup2 # mount /dev/mapper/backup2 /backup2
See how to run fsck On LUKS (dm-crypt) based LVM physical volume for more details.
How do I change LUKS passphrase (password) for encrypted partition?
Type the following command
### see key slots, max -8 i.e. max 8 passwords can be setup for each device #### # cryptsetup luksDump /dev/xvdc # cryptsetup luksAddKey /dev/xvdc
Enter any passphrase: Enter new passphrase for key slot: Verify passphrase:
Remove or delete the old password:
# cryptsetup luksRemoveKey /dev/xvdc
Please note that you need to enter the old password / passphrase.