Difference between revisions of "User:Indigo"

Revision as of 11:05, 11 August 2013

I am from Germany. I have interests in security-related subjects and follow pages here on a variety of networking and encryption topics. The distro I have used most is Debian, interrupted by stints to Ubuntu. I have been using Arch since Mid 2011. Feel free to leave comments on the talk page here or send me an email via the wiki interface.

Work-in-progress page

Mind you: I was not using Arch yet when most of the following section was written. It is saved here because we re-worked the original considerably. This will be deleted in Sept 13.

Encrypting a LVM setup

It's really easy to use encryption with LVM. If you do not know how to set up LVM, then read Installing with Software RAID or LVM.

LVM on LUKS

The easiest and best method is to set up LVM on top of the encrypted partition instead of the other way round. This link here is easy to follow and explains everything: Arch Linux: LVM on top of an encrypted partition

The most important thing in setting LVM on top of encryption is to configure the initramfs for running both the encrypt hook and the lvm2 hook (and those two before the filesystems hook). In the past, it was necessary to ensure the correct ordering of these hooks in /etc/mkinitcpio.conf but the order no longer matters with the current implementation of lvm2.

LUKS on LVM

To use encryption on top of LVM, you have to first set up your LVM volumes and then use them as the base for the encrypted partitions. That means, in short, that you have to set up LVM first. Then follow this guide, but replace all occurrences of /dev/sdXy in the guide with its LVM counterpart. (E.g.: /dev/sda5 -> /dev/<volume group name>/home). This is used to setup partitions (inside the LVM) which can be unlocked separately or a mixture of encrypted and non-encrypted partitions.

For encrypted partitions inside an LVM, the LVM-hook has to run first, before the respective encrypted logical volumes can be unlocked. So for this add the encrypt hook in /etc/mkinitcpio.conf after the lvm2 hook, if you chose to set up encrypted partitions on top of LVM.

LVM with Arch Linux Installer (>2009.08 <2012.07.15)

In between Arch Linux installation media release 2009.08 and 2012.07.15 LVM and dm_crypt had been supported by the installer out of the box. This made it very easy to configure a system for LVM on dm-crypt or vice versa. Actually the configuration is done exactly as without LVM: see the corresponding section above. It differs only in two aspects.

The partition and filesystem choice

Create a small, unencrypted boot partition and use the remaining space for a single partition which can later be split up into multiple logic volumes by LVM.

For a LVM-on-dm-crypt system set up the filesystems and mounting points for example like this:

/dev/sda1   raw->ext2;yes;/boot;no_opts;no_label;no_params
/dev/sda2   raw->dm_crypt;yes;no_mountpoint;no_opts;sda2crypt;-c_aes-xts-plain_-y_-s_512
/dev/mapper/sda2crypt   dm_crypt->lvm-vg;yes;no_mountpoint;no_opts;no_label;no_params
/dev/mapper/sda2crypt+  lvm-pv->lvm-vg;yes;no_mountpoint;no_opts;cryptpool;no_params
/dev/mapper/cryptpool   lvm-vg(cryptpool)->lvm-lv;yes;no_mountpoint;no_opts;cryptroot;10000M|lvm-lv;yes;no_mountpoint;no_opts;crypthome;20000M
/dev/mapper/cryptpool-cryptroot   lvm-lv(cryptroot)->ext3;yes;/;no_opts;cryptroot;no_params
/dev/mapper/cryptpool-crypthome   lvm-lv(crypthome)->ext3;yes;/home;no_opts;cryptroot;no_params

The configuration stage

• In /etc/mkinitcpio.conf add the encrypt hook before the lvm2 hook in the HOOKS array, if you set up LVM on top of the encrypted partition.

That is it for the LVM & dm_crypt specific part. The rest is done as usual.

• In /etc/rc.conf set USELVM to "yes".

Applying this to a non-root partition

You might get tempted to apply all this fancy stuff to a non-root partition. Arch does not support this out of the box, however, you can easily change the cryptdev and cryptname values in /lib/initcpio/hooks/encrypt (the first one to your /dev/sd* partition, the second to the name you want to attribute). That should be enough.

The big advantage is you can have everything automated, while setting up /etc/crypttab with an external key file (i.e. the keyfile is not on any internal hard drive partition) can be a pain - you need to make sure the USB/FireWire/... device gets mounted before the encrypted partition, which means you have to change the order of /etc/fstab (at least).

Of course, if the cryptsetup package gets upgraded, you will have to change this script again. However, this solution is to be preferred over hacking /etc/rc.sysinit or similar files. Unlike /etc/crypttab, only one partition is supported, but with some further hacking one should be able to have multiple partitions unlocked.

If you want to do this on a software RAID partition, there is one more thing you need to do. Just setting the /dev/mdX device in /lib/initcpio/hooks/encrypt is not enough; the encrypt hook will fail to find the key for some reason, and not prompt for a passphrase either. It looks like the RAID devices are not brought up until after the encrypt hook is run. You can solve this by putting the RAID array in /boot/grub/menu.lst, like

kernel /boot/vmlinuz-linux md=1,/dev/hda5,/dev/hdb5

If you set up your root partition as a RAID, you will notice the similarities with that setup ;-). GRUB can handle multiple array definitions just fine:

kernel /boot/vmlinuz-linux root=/dev/md0 ro md=0,/dev/sda1,/dev/sdb1 md=1,/dev/sda5,/dev/sdb5,/dev/sdc5

LVM and dm-crypt manually (short version)

Notes

If you are smart enough for this, you will be smart enough to ignore/replace LVM-specific things if you do not want to use LVM.

Partitioning scheme

/dev/sda1 -> /boot
/dev/sda2 -> LVM

The commands

cryptsetup -d /dev/random -c aes-xts-plain -s 512 create lvm /dev/sda2
dd if=/dev/urandom of=/dev/mapper/lvm
cryptsetup remove lvm
lvm pvcreate /dev/sda2
lvm vgcreate lvm /dev/sda2
lvm lvcreate -L 10G -n root lvm
lvm lvcreate -L 500M -n swap lvm
lvm lvcreate -L 500M -n tmp lvm
lvm lvcreate -l 100%FREE -n home lvm
cryptsetup luksFormat -c aes-xts-plain -s 512 /dev/lvm/root
cryptsetup luksOpen /dev/lvm/root root
mkreiserfs /dev/mapper/root
mount /dev/mapper/root /mnt
dd if=/dev/zero of=/dev/sda1 bs=1M
mkreiserfs /dev/sda1
mkdir /mnt/boot
mount /dev/sda1 /mnt/boot
mkdir -p -m 700 /mnt/etc/luks-keys
dd if=/dev/random of=/mnt/etc/luks-keys/home bs=1 count=256

Install Arch Linux

Run /arch/setup

Configuration

/etc/rc.conf

Change USELVM="no" to USELVM="yes".

/etc/mkinitcpio.conf

Put lvm2 and encrypt (in that order) before filesystems in the HOOKS array. Again, note that you are setting encryption on top of LVM.)

if you want install the system on a usb stick, you need to put usb just after udev.

/boot/grub/menu.lst

Change root=/dev/hda3 to root=/dev/lvm/root.

For kernel >= 2.6.30, you should change root=/dev/hda3 to the following:

cryptdevice=/dev/lvm/root:root root=/dev/mapper/root

if you want install the system on a usb stick, you need to add lvmdelay=/dev/mapper/lvm-root

/etc/fstab

/dev/mapper/root        /       reiserfs        defaults        0       1
/dev/sda1               /boot   reiserfs        defaults        0       2
/dev/mapper/tmp         /tmp    tmpfs           defaults        0       0
/dev/mapper/swap        none    swap            sw              0       0

/etc/crypttab

swap	/dev/lvm/swap	SWAP		-c aes-xts-plain -h whirlpool -s 512
tmp	/dev/lvm/tmp	/dev/urandom	-c aes-xts-plain -s 512

After rebooting

The commands

cryptsetup luksFormat -c aes-xts-plain -s 512 /dev/lvm/home /etc/luks-keys/home
cryptsetup luksOpen -d /etc/luks-keys/home /dev/lvm/home home
mkreiserfs /dev/mapper/home
mount /dev/mapper/home /home

/etc/crypttab

home	/dev/lvm/home   /etc/luks-keys/home

/etc/fstab

/dev/mapper/home        /home   reiserfs        defaults        0       0

/ on LVM on LUKS

Make sure your kernel command line looks like this:

root=/dev/mapper/<volume-group>-<logical-volume> cryptdevice=/dev/<luks-part>:<volume-group>

For example:

root=/dev/mapper/vg-arch cryptdevice=/dev/sda4:vg

Or like this:

cryptdevice=/dev/<volume-group>/<logical-volume>:root root=/dev/mapper/root

AIF Instructions

(saved here or intermediate reference upon rm'ing the section in the LUKS wiki

Prepare hard drive for AIF

Now that /dev/mapper/root and /dev/mapper/home are in place, we can enter the regular Arch setup script to install the system into the encrypted volumes.

# /arch/setup

Skip the Partitioning and Auto-Prepare steps and go straight to manual configuration. Instead of choosing the hardware devices (/dev/sdaX) directly, you have to select the mapper devices created above. Choose /dev/mapper/root for your root and /dev/mapper/home as /home partition respectively and format them with any filesystem you like. The same is valid for a swap partition which is set up like the /home partition. Make sure you mount /dev/sda1 as the /boot partition, or else the installer will not properly set up the bootloader.

Select and Install packages

Select and install the packages as usual: the base package contains all required programs.

Exit Install

Now that the install is finished the only thing left to do is add entries to the /etc/crypttab file so you do not have to enter the passphrase for all encrypted partitions. This works only for non-root partitions e.g. /home, swap, etc.

# vi /mnt/etc/crypttab

Add one of the following for the /home partition.

home    /dev/sda5    /etc/mypassword1

You can also use a keyfile instead of a passphrase. If not already done, create a keyfile and add the key to the corresponding LUKS partition as described above. Then add the following information to the /etc/crypttab file for automounting:

home    /dev/sda5    /path/of/your/keyfile

If you used a USB device to store your keyfile, you should have something like this:

home    /dev/sda5    /dev/sd*1/keyfile

Or if the keyfile was stored in the MBR, it should be like this:

home    /dev/sda5    /dev/sd*:2048:2048

After rebooting you should now be presented with the text

A password is required to access the root filesystem:

followed by a prompt for a LUKS password. Type it in and everything should boot. Once you have logged in, have a look at your mounted partitions by typing mount. You should have /dev/mapper/root mounted at / and, if you set up a separate encrypted home partition, /dev/mapper/home mounted at /home. If you set up encrypted swap, swapon -s should have /dev/mapper/swap listed as your swap partition.

GRUB Legacy

GRUB Legacy: You have to make some small changes to the entries generated by the installer by replacing /dev/mapper/root with /dev/sda3. The important point to remember here is to use the same cryptdevice name you assigned when you initially unlocked your device. In this example, the device name is cryptroot; customize yours accordingly:

# (0) Arch Linux
title Arch Linux
root (hd0,0)
kernel /vmlinuz-linux cryptdevice=/dev/sda3:cryptroot root=/dev/mapper/cryptroot ro
initrd /initramfs-linux.img

For kernels older than 2.6.37, the syntax is:

# (0) Arch Linux
title Arch Linux
root (hd0,0)
kernel /vmlinuz26 root=/dev/sda3 ro
initrd /kernel26.img

LILO

LILO: Edit the Arch Linux section in /etc/lilo.conf and include a line for the append option, over the initrd, with the root=/dev/sda3 parameter. The append section makes the same kernel line as in GRUB. Also, you can omit the root option above the image option. The section looks like this:

# Arch Linux lilo section
image = /vmlinuz-linux
# root = /dev/sda3
 label = Arch
 initrd = /initramfs-linux.img
 append = "root=/dev/sda3"
 read-only

If you want to use a USB flash drive with a keyfile, you have to append the cryptkey option. See the corresponding section above.