I had submitted a document to this list a few weeks back that gave instructions
for whole disk encryption which would cover /tmp /home /swap and everything
other than /boot. I did not ask for space in the wiki because i thought it was
waiting for "peer review" for accuracy. That entire thread seemed to
simply die so I haven't pursued the wiki any further. I already have this
document in a wiki format at work and would be happy to submit it to the CentOS
wiki should it pass muster. The contents of my last post are:
Whole (Most) Disk Encryption on CentOS 5
This document is in the process of being developed
Credit To Others
The primary source for this document was
http://www.tummy.com/Community/Articles/cryptoroot-f8/. It was heavily used but
adapted to CentOS5 and with some changes which simplify and improve the process.
Other sources that were used are http://musialek.org/?p=3 and
http://agiletesting.blogspot.com/2008/05/encrypting-linux-root-partition-with.html.
Summary
This document contains step by step instructions for encrypting the entire disk
including swap space with the exception of the /boot partition on CentOS 5. It
assumes that you are planning to encrypt your disk from install and that your
disk is /dev/sda. This document was created with with CentOS 5.0 before any
patches or updates were applied. There are some optional components within this
document that are not technically necessary for encrypting the disk. Those
components can be ignored for testing, but they should be followed on any ?real?
systems.
The end of the document contains optional configurations. This is useful if you
prefer to have additional partitions on the disk. The step by step instructions
will leave a disk with two partitions, /boot (/dev/sda1) and an LVM (/dev/sda2)
partition which contains all system volumes. The optional section will contain
the differences needed to have an additional partition (/dev/sda3) which may be
used as a data store, NFS share, etc.
Step One: Prepare the disk
The first step is to prepare the disk. The installer partitioning software
doesn't have the flexibility to be able to do this, so you will need to
switch to the shell and perform the setup manually.
Once the installer has moved into the GUI, press Ctrl-Alt-F2 to get a command
prompt.
OPTIONAL ? Overwrite and randomize the entire disk. Use shred or dd to overwrite
the disk. The technical merits of multiple overwrites of shred vs. using
/dev/random with dd are beyond the scope of this document. The default options
of shred take a very, very long time to run. The time to complete on any
sizeable disk would likely be measured in days. This note applies to all
statements about radomizing the disks or partitions in this document.
# shred -v /dev/sda
or
# dd if=/dev/urandom of=/dev/sda
Use fdisk to create the partitions for install. You will need to create a /boot
partition and an LVM partition at the end of the disk. The gap in between the
two partitions will become your encrypted file-system. This document will refer
to the boot partition as /dev/sda1 and the install partition at the end of the
disk as /dev/sda3. The encrypted partition will become /dev/sda2.
The partition at the end of the disk should be smaller than the empty space
between /boot and your LVM partition so that there is room for the meta-data
associated with the encryption. The LVM partition really only needs to be large
enough to install the system. You will be able to expand the system volumes if
you like after you have a working, encrypted system.
# fdisk /dev/sda
RedHat documentation recommends 100MB for the boot partition. Over time, the
/boot partition can fill up as a result of updated kernels if it is not
regularly cleaned. Using a larger /boot partition may be beneficial. /dev/sda1
should be of type 83 (Linux) and should be bootable. /dev/sda3 should have
sufficient space to perform the installation. The partition type of /dev/sda3
should be 8e (Linux LVM). When done, it should look something like:
Device Boot Start End Blocks Id System
/dev/sda1 * 1 65 521955 83 Linux
/dev/sda3 20000 30401 83554065 8e Linux LVM
If you are not familiar with the fdisk commands, you can type ??? at the fdisk
prompt to see a list of commands. Once you have the disk partitioned correctly
(view the partition table with the ?p? command within fdisk), remember to write
the partition table while exiting with the ?w? command.
Return to the GUI to complete the installation. Press Ctrl-Alt-F6 to return to
the GUI.
Step Two: Installing the OS
The installation must be done using the graphical installer because the text
installer doesn't allow a custom installation to use LVM.
For the partitioning, select ?Custom?, and tell it to format sda1 as /boot, and
sda3 as an LVM physical partition.
Then use the ?LVM? button to create a volume group, and a logical volumes within
it for the / file-system. Create the swap partition within LVM to ensure that
your swap space is ultimately encrypted as well. You can create /usr, /var,
/tmp, and other volumes within LVM if you choose. Note that you'll be able
to resize the partitions later, so they don't need to be the desired target
space or proportion right now.
Complete the rest of the installation process as normal.
Step Three: Create the encrypted partition
Boot into the installed system and create /dev/sda2 using fdisk. It needs to be
the space between sda1 and sda3, and it should have a partition type of 83
(Linux) (it does not need to be type 8e, Linux LVM). Write the partition table
and quit fdisk.
Once you have create the partition, use the partprobe command to read new
partition.
# partprobe
If you did not randomize the disk via shred or dd, you should randomize the
partition using dd. This may take a while depending on the size of the
partition.
# dd if=/dev/urandom of=/dev/sda2
You now need to set up encryption.
# cryptsetup --key-size 256 --verbose --verify-passphrase --cipher
aes-cbc-essiv:sha256 luksFormat /dev/sda2
Confirm that you want to destroy all data on the partition and then provide a
pass-phrase. You will need to remember the pass-phrase in order to access your
system.
Open the encrypted file-system to ensure that all is well with the encrypted
partition
# /sbin/cryptsetup luksOpen /dev/sda2 lvm
Enter the pass-phrase for the file-system. Close the file-system with
# /sbin/cryptsetup luksClose lvm
OPTIONAL - Additional pass-phrases can be added at this point. This is
especially useful in enterprise environments where you would like to have an
administrative pass-phrase should a user forget the pass-phrase or you need to
have access after a user leaves.
# /sbin/cryptsetup luksAddKey /dev/sda2
Enter the existing pass-phrase twice, it will then ask you to enter a new
pass-phrase where you can add the second key. You can verify that you now have 2
keys by using the luksOpen option with the cryptsetup command using each
password or by using the command
# /sbin/cryptsetup luksDump /dev/sda2
The output will look similar to
Version: 1
Cipher name: aes
Cipher mode: cbc-essiv:sha256
Hash spec: sha1
Payload offset: 2056
MK bits: 256
MK digest: f3 6e 66 7c d2 40 1c 4e 6e ce fa d5 b9 ac 3b 13 f9 a0 9c 7d
MK salt: 2b f2 38 ff 21 0a 31 cd a9 17 97 a9 c0 ad 72 46
e3 78 21 b2 03 1a d1 68 a3 2d 80 61 bf d0 09 4d
MK iterations: 10
UUID: ca858575-a412-4d26-bde7-7dfdfd0f6a72
Key Slot 0: ENABLED
Iterations: 51953
Salt: 69 51 dc 85 57 84 9d c1 97 5c ef a6 d5 31 6d d2
4f 8b ce 90 71 90 8c 6c 3f 81 b7 75 41 85 59 5b
Key material offset: 8
AF stripes: 4000
Key Slot 1: ENABLED
Iterations: 52068
Salt: c7 a6 e5 e9 08 d1 d6 80 c5 0a fe f5 74 22 2e 74
63 a3 e3 41 f3 4f 82 fe 54 7d 5d 99 0b 14 8c 80
Key material offset: 264
AF stripes: 4000
Key Slot 2: DISABLED
Key Slot 3: DISABLED
Key Slot 4: DISABLED
Key Slot 5: DISABLED
Key Slot 6: DISABLED
Key Slot 7: DISABLED
Step Four: Configure mkinitrd for encrypted system
Make a backup copy of /sbin/mkinitrd. Future updates of the mkinitrd package
will overwrite it, but the changes will allow future kernel updates to properly
build an initrd. Modify /sbin/mkinitrd per the patch below. The patch modifies
the MODULES line so that initrd has the proper modules for encryption, adds
cryptsetup to initrd, and configures initrd to open the encrypted file-system.
>--- /sbin/mkinitrd.before.dm-crypt.20080811 2008-08-11
23:17:04.000000000 -0400
+++ /sbin/mkinitrd 2008-08-14 18:52:31.000000000 -0400
@@ -40,7 +40,7 @@
VERSION=5.1.19.6
PROBE="yes"
-MODULES=""
+MODULES="aes sha256 dm_crypt cbc"
PREMODS=""
DMDEVS=""
NET_LIST=""
@@ -1081,6 +1081,7 @@
fi
inst /sbin/nash "$MNTIMAGE/bin/nash"
inst /sbin/insmod.static "$MNTIMAGE/bin/insmod"
+inst /sbin/cryptsetup "$MNTIMAGE/bin/cryptsetup"
ln -s /sbin/nash $MNTIMAGE/sbin/modprobe
for MODULE in $MODULES; do
@@ -1264,6 +1265,10 @@
# things like RAID or LVM
emit "mkblkdevs"
+# Adding stuff for dm-cyrpted root partition
+emit "echo Decrypting root device"
+emit "cryptsetup luksOpen /dev/sda2 lvm"
+
emitdms
if [ -n "$raiddevices" ]; then
NOTE: If you choose to modify the /sbin/mkinitrd file manually, the additions
for ?cryptsetup luksOpen /dev/sda2 lvm? should occur after the SECOND occurance
of ?emit mkblkdevs?
OPTIONAL ? You can prevent the mkinitrd script from being updated via yum by
modifying /etc/yum.conf to include the line
exclude=mkinitrd nash
Step Five: Build new initrd
You now need to create the new initrd that will allow the system to boot using
the encrypted device. The method used here will allow the presence of both the
encrypted system and the unencrypted system on the computer. This provides the
opportunity to ensure that the encrypted system is working properly and to boot
into the unencrypted system should any modifications be needed.
# mkinitrd -v /boot/initrd-2.6.18-8.el5.crypt.img 2.6.18-8.el5
Step Six: Copy the LVM to the encrypted partition
Make sure that any modifications to the system configurations such as the
modified mkinitrd or the modified yum.conf are done before performing this step.
Although those things can be duplicated on the encrypted system, it is easier if
they don't need to be repeated.
Reboot the system into single user mode.
Open the encrypted file-system
# /sbin/cryptsetup luksOpen /dev/sda2 lvm
Enter the pass-phrase. Now you can copy the contents of sda3 to the encrypted
sda2.
# dd if=/dev/sda3 of=/dev/mapper/lvm
When it's done, close the encrypted partition with:
# /sbin/cryptsetup luksClose lvm
Step Seven: Modify grub.conf to boot the encrypted system
Add the following lines to the end of /boot/grub/grub.conf. This can be done
while still in single user mode.
title CentOS Encrypted System (2.6.18-8.el5)
root (hd0,0)
kernel /vimlinuz-2.6.18-8.el5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet
initrd /initrd-2.6.18-8.el5.crypt.img
NOTE: To make the encrypted system the default system, make the above lines the
first block listed in grub.conf
Step Eight: Extend encryption to the entire disk
NOTE: The /boot partition will not be encrypted, however the rest of the disk
will be.
Once the encrypted system is confirmed to be working correctly, remove the
unencrypted system. Randomize /dev/hda3 by using either shred or dd. Once this
step is performed, there is no turning back. The unencrypted system will no
longer exist on the disk. It is also safe to remove the grub.conf entries for
the unencrypted system.
# shred -v /dev/sda3
or
# dd if=/dev/urandom of=/dev/sda3
Use the fdisk command to resize sda2 to fill the entire disk.
# fdisk /dev/sda
Within fdisk, delete /dev/sda2 and /dev/sda3. Create a new /dev/sda2 that fills
the entire disk. When adding the new /dev/sda2 the defaults should be
sufficient.
Write the changes to the partition table. Use partprobe to detect changes to the
partition table.
# partprobe
Step Nine: Resize the file-systems
First, resize the crypto device.
# cryptsetup resize lvm
Next, resize the physical volume in the volume group:
# pvresize ?-setphysicalvolumesize [size of disk - /boot] /dev/mapper/lvm
In order to resize the LVM volumes to use the entire disk, a reboot is required.
NOTE to testers This seems strange to me and seems to defeat one of the primary
strengths of using LVM, but I was unable to extend the logical volumes beyond
the original number of physical extents until after a reboot. I will do some
more with this to see if it can be done without the reboot.
Extend the logical volumes of the system with lvextend. man lvextend for more
information on the command.
# lvextend -L +[size to increase the volume] /dev/VolGroup00/LogVol00
Resize each of the file-systems with:
# resize2fs /dev/VolGroup00/LogVol00
Replace VolGroup00 and LogVol00 with the correct volume group names and logical
volume names for each volume on the system.
Optional Configurations
A: Encrypting Additional Partitions
A.1: Create the encrypted system
This step is optional. If the goal is to have the entire system encrypted,
follow steps 1-7 above. The only difference is that when creating /dev/sda2 in
fdisk, only make it as large as you want your system volumes to use. If
/dev/sda2 is larger than /dev/sda3 and you wish to change the volume sizes for
the system volumes, follow step 9 from above.
A.2: Create partition
Because /dev/sda3 as used for install only needed to be large enough to perform
the installation, the partition should now be enlarged to the desired size.
Randomize /dev/hda3 by using either shred or dd. Once this step is performed,
there is no turning back. The unencrypted system will no longer exist on the
disk. It is also safe to remove the grub.conf entries for the unencrypted
system.
# shred -v /dev/sda3
or
# dd if=/dev/urandom of=/dev/sda3
Use the fdisk command to resize sda3.
# fdisk /dev/sda
Within fdisk, delete /dev/sda3. Create a new /dev/sda3 that follows /dev/sda2
and is of the desired size. If /dev/sda3 is intended to fill the remainder of
the disk, the defaults should be sufficient.
Write the changes to the partition table. Use partprobe to detect changes to the
partition table.
# partprobe
A.3: Create the file system
Create the new file system on /dev/sda3
# mkfs -t ext3 /dev/sda3
A.4: Encrypt the file system
This step is essentially the same as step 3 above. The difference being the
device encrypted and a different mapper device name should be used.
# cryptsetup --key-size 256 --verbose --verify-passphrase --cipher
aes-cbc-essiv:sha256 luksFormat /dev/sda3
# /sbin/cryptsetup luksOpen /dev/sda3 myencryptedpartition
# /sbin/cryptsetup luksClose myencryptedpartition
OPTIONAL - Add additional pass-phrases. A key file can be used to prevent the
need for typing in a pass-phrase every time the file-system is mounted.
# /sbin/cryptsetup luksAddKey /dev/sda3
or
# /sbin/cryptsetup luksAddKey /dev/sda3 /path/and/keyfile
A.5: Configure encrypted partitions to mount at boot
This step simplifies the use of an encrypted file system. It will allow the
encrypted file system to be treated as any non-encrypted system. The file
/etc/crypttab will automate the luksOpen commands that were used earlier. The
format of the /etc/crypttab is
mappingname devicename password_file_path options
Not all fields are needed. Most of the possible options for the options field
are ignored for LUKS volumes, because LUKS volumes have all the necessary
information about the cipher, key size, and hash in the volume header. Also, if
the password_file_path field is empty or has the value ?none?, the system will
prompt for the pass-phrase when mounting the file system.
Create /etc/crypttab
myencryptedpartition /dev/sda3 /path/and/keyfile
or
myencryptedpartition /dev/sda3 none
It is usually a bad idea to store the pass-phrase in a plain text file, however,
an encrypted root partition does alleviate some of the concern. Under no
circumstances should a pass-phrase be stored on an unencrypted partition such as
/boot.
Modify /etc/fstab to add the line
/dev/mapper/myencryptedparition /myFileSystem ext3 defaults
1 2
The encrypted partition is now configured to mount at boot.
----------------------------------------> Date: Wed, 15 Oct 2008 07:52:40 -0400
> From: maxhetrick at verizon.net
> To: centos-docs at centos.org
> Subject: [CentOS-docs] Encrypting tmp swap and home
>
> Hi everyone,
>
> I added a page under the HowTos for Encryption, and then added a guide
> for encrypting /tmp /swap and /home using cryptsetup and LUKS keys on
> LVM, when you already have partitions setup.
>
> http://wiki.centos.org/HowTos/EncryptTmpSwapHome
>
> Regards,
> Max
> _______________________________________________
> CentOS-docs mailing list
> CentOS-docs at centos.org
> http://lists.centos.org/mailman/listinfo/centos-docs
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