Suppose you have a portable USB drive to use with your Linux system. If you are security conscious, you may want to encrypt your USB drive, so that no one else tamper with content in your USB drive. For that, you can use dm-crypt and LUKS, which together provide transparent encryption of block devices by using device mapper subsystem.
To encrypt a partition using dm-crypt+LUKS on Linux, install the following.
On Ubuntu, Mint or Debian:
On CentOS, Fedora or RHEL:
Using fdisk, create a new partition to encrypt as follows. In this example, I assume that /dev/sdb is mapped to your hard drive to encrypt.
A newly created partition to use with LUKS is mapped to /dev/sdb1. Initialize this partition by using cryptsetup command. This command will overwrite the partition with random data, and prompt you for an initial passphrase to use.
You can check LUKS configuration of the partition by running the following command, which will dump LUKS header information.
LUKS header information for /dev/sdb1 Version: 1 Cipher name: aes Cipher mode: cbc-essiv:sha256 Hash spec: sha1 Payload offset: 4096 MK bits: 256 MK digest: 18 1d 6d 3e e9 44 2a fe bf 67 78 8f aa 02 7f 91 2a f4 f2 17 MK salt: 26 cc 29 9f 0b 7d ea ff 44 9f fe 34 91 40 6e 9b af 1e bd 8f d0 d2 1c 3a 70 30 35 5f 2d 49 9a 95 MK iterations: 222875 UUID: 5acc17e0-80be-40ba-beae-626e47b57379 Key Slot 0: ENABLED Iterations: 891733 Salt: 26 20 29 39 a5 1d 02 7b ca 8c bd 18 bc 29 64 7e 28 dc 06 65 78 0e 16 95 1a 67 14 66 12 2d a3 c1 Key material offset: 8 AF stripes: 4000 Key Slot 1: DISABLED Key Slot 2: DISABLED Key Slot 3: DISABLED Key Slot 4: DISABLED Key Slot 5: DISABLED Key Slot 6: DISABLED Key Slot 7: DISABLED
Next, open the LUKS partition as follows.
The above command will ask you to enter a passphrase. Once the LUKS partition is successfully opened with a correct passphrase, the encrypted partition will be mapped to /dev/mapper/sdb1. To check if this block device is created successfully, use this command:
Disk /dev/mapper/sdb1: 1067 MB, 1067156992 bytes 255 heads, 63 sectors/track, 129 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x7b0402f6
Finally, you can create a new filesystem on /dev/mapper/sdb1, and mount it on your Linux system:
$ sudo mount /dev/mapper/sdb1 /mnt
Mount LUKS-Encrypted Hard Drive Automatically on Boot
If you want to have your LUKS-encrypted partition mounted automatically upon boot, follow this procedure.
First, create a randomly generated key file used to open the encrypted partition during boot sequence. Make this key file readable by the root only.
$ sudo chmod 400 /root/key.sdb1
Add the key file to LUKS configuration:
Verify that the key file has been successfully added:
Key Slot 0: ENABLED Iterations: 891733 Salt: 26 20 29 39 a5 1d 02 7b ca 8c bd 18 bc 29 64 7e 28 dc 06 65 78 0e 16 95 1a 67 14 66 12 2d a3 c1 Key material offset: 8 AF stripes: 4000 Key Slot 1: ENABLED Iterations: 404242 Salt: 9d b9 05 d4 06 be 8c db 74 bd cb 59 de 9a 95 8a 91 8c 09 5d 91 5f 0a e6 b5 86 3c 81 73 22 e1 db Key material offset: 264 AF stripes: 4000
As you can see above, the key slot 1 has been occupied with the key file.
Next, obtain the UUID of the encrypted block device.
Now, edit /etc/crypttab to add the following entry.
sdb1 /dev/disk/by-uuid/5acc17e0-80be-40ba-beae-626e47b57379 /root/key.sdb1 luks
The format of the entry in /etc/crypttab is as follows.
<name of encrypted block device> /dev/disk/by-uuid/<UUID of block device> <location of key file> luks
Finally, create a mount point, and edit /etc/fstab to add mount point information:
$ sudo vi /etc/fstab
/dev/mapper/sdb1 /mnt_sdb1 ext3
Reboot now. The encrypted partition should be auto-mounted upon boot up.
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