433 lines
No EOL
14 KiB
Markdown
433 lines
No EOL
14 KiB
Markdown
# Installing a cloud server with full disk encryption
|
|
|
|
For hosting purposes, I am installing a new server on [Kimsufi](kimsufi.com/). This is a French public cloud provider (property of [OVH](ovh.com/)).
|
|
|
|
It is well known that, at [Deuxfleurs](https://deuxfleurs.fr), we do not fancy hosting in datacenters: because of the lack on control on our machines, and potential privacy threats. In essence, people at Kimsufi could easily -- and without me knowing -- read my hard drive, and thus any sensitive user data stored inside.
|
|
|
|
For that reason, I want to make it harder for their staff to access my data. A good first line of defense for that purpose is to encrypt the whole disk (*aka* Full Disk Encryption). Note that motivated attackers with physical access to my server would easily overcome the encryption. **If you really care about who accesses your data, keep your hard drives closest to you, e.g. at your home.**
|
|
|
|
---
|
|
|
|
Long story short: this guide presents a step-by-step installation of Debian buster on Kimsufi, using the [`dm-crypt`](https://wiki.archlinux.org/index.php/Dm-crypt) Linux kernel subsystem to encrypt the `/` and the `swap` partitions.
|
|
Because I don't have physical access to the server, I need a way to *remotely enter the disk decryption password*, that is `dropbear` (a lightweight SSH server) inside `initramfs` (a minimal operating system that runs from RAM, before Linux boots).
|
|
|
|
If you plan on doing the same without Kimsufi, know that it makes no difference: I am basically using a "rescue" console on another computer to configure `/dev/sda` (my server's system drive) for booting Linux with encrypted partitions.
|
|
|
|
I must credit several useful guides that helped me succeed:
|
|
|
|
* [OpsBlog guide on installing Linux with full-disk encryption and DropBear SSH on Kimsufi](https://opsblog.net/posts/full-disk-encrypted-ubuntu-kimsufi-sever/)
|
|
|
|
DropBear allows SSH connection before boot, to remotely decrypt the main partition.
|
|
|
|
* [Debian guide on installing Debian from a Linux system](https://www.debian.org/releases/wheezy/mipsel/apds03.html.en)
|
|
|
|
|
|
|
|
## Overview of steps
|
|
|
|
* Boot the Kimsufi server in rescue mode (gives you a remote shell with access to your system's hard drive).
|
|
|
|
* Wipe filesystem, format partitions. I basically want:
|
|
|
|
* A "cleartext" `/boot` partition
|
|
* An encrypted `/` partition
|
|
* An encrypted swap partition
|
|
|
|
Docs on the encrypted swap:
|
|
* [ArchLinux wiki: dm-crypt - Swap encryption](https://wiki.archlinux.org/index.php/Dm-crypt/Swap_encryption)
|
|
* [cryptsetup FAQ](https://gitlab.com/cryptsetup/cryptsetup/-/wikis/FrequentlyAskedQuestions#2-setup): see "2.3 How do I set up encrypted swap?"
|
|
|
|
* Install and configure Debian (including disk cryptography and decryption through SSH).
|
|
|
|
* Boot and log into the server.
|
|
|
|
* Setup automated decryption from a remote (in case of reboot).
|
|
|
|
## Detailed process
|
|
|
|
### Boot the server in rescue mode
|
|
|
|
* Go to the Kimsufi admin panel, click "NetBoot", select "Rescue", pick "rescue64-pro", clock "Next", "Confirm", and then click the "Reboot" button on the admin panel.
|
|
|
|
* Kimsufi will mail you the root password for you to log into the server in rescue mode.
|
|
|
|
* Will likely cause an error from your SSH client, since the fingerprint of the server differs from the usual one.
|
|
|
|
You should end up with a shell that has access to `/dev/sda`, your server's drive.
|
|
|
|
### Wipe filesystem & format partitions
|
|
|
|
Target partition table:
|
|
|
|
```
|
|
+-----------+--------------------+-----------+--------------------+
|
|
Name: | /dev/sda1 | /dev/sda2 | /dev/sda3 | /dev/sda4 |
|
|
| | | | |
|
|
| | | | |
|
|
| | +------------------+ | +------------------+
|
|
| | | /dev/mapper/swap | | | /dev/mapper/main |
|
|
Format: | none | | swap | ext4 | | ext4 |
|
|
Size: | 1MiB | | 8GiB | 512MiB | | remaining space |
|
|
Flags: | bios_grub | | | | | |
|
|
Mount: | | | swap | /boot | | / |
|
|
+-----------+-+------------------+-----------+-+------------------+
|
|
```
|
|
|
|
We use GPT partition table layout (without UEFI), which demands a small `bios_grub` partition at the beginning of the drive (stores GRUB's `core.img`). Hence `/dev/sda1`. See:
|
|
|
|
* [Wikipedia: BIOS boot partition](https://en.wikipedia.org/wiki/BIOS_boot_partition)
|
|
* [GNU: BIOS installation](https://www.gnu.org/software/grub/manual/grub/html_node/BIOS-installation.html#BIOS-installation)
|
|
* [ArchLinux wiki: Partitioning](https://wiki.archlinux.org/index.php/partitioning#Partition_table)
|
|
* [Gentoo wiki: Installation - Disks](https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Disks#Partition_tables)
|
|
|
|
|
|
* Wipe all information about previous filesystem:
|
|
|
|
DANGER!!! DANGER!!! WIPES EVERYTHING FROM YOUR DISK!!!
|
|
|
|
```bash
|
|
wipefs -a /dev/sda
|
|
```
|
|
|
|
* Create GPT disk layout
|
|
|
|
```bash
|
|
# Create GPT layout
|
|
parted -a optimal /dev/sda mklabel gpt
|
|
# Create first 1MiB bios_grub partition
|
|
parted /dev/sda -a optimal mkpart bios_grub 0% 1MiB
|
|
parted /dev/sda set 1 bios_grub on
|
|
# Create third 8GiB swap partition
|
|
parted /dev/sda -a optimal mkpart swap 1MiB 8001MiB
|
|
# Create second 512MiB /boot partition
|
|
parted /dev/sda -a optimal mkpart boot 8001MiB 8513MiB
|
|
# Create last / partition using all remaining space
|
|
parted /dev/sda -a optimal mkpart main 8513MiB 100%
|
|
# Set first partition as bootable
|
|
```
|
|
|
|
* Format partitions
|
|
|
|
* The ext4 boot partition
|
|
|
|
Format it like so:
|
|
|
|
```bash
|
|
mkfs.ext4 /dev/sda3
|
|
```
|
|
|
|
* The encrypted swap partition
|
|
|
|
All configuration of the encrypted swap partition comes after the OS installation.
|
|
|
|
* The encrypted main partition
|
|
|
|
```bash
|
|
# Set it up using cryptsetup (I searched for good parameters):
|
|
cryptsetup --type luks2 --cipher aes-xts-plain64 --hash sha256 --iter-time 2000 --key-size 512 luksFormat /dev/sda4
|
|
|
|
# Get the UUID, save it for later:
|
|
cryptsetup luksDump /dev/sda4 | grep UUID | awk '{print $2}'
|
|
# Example output: 09762476-ba7c-4732-8856-44a716c23339
|
|
|
|
# Decrypt the partition:
|
|
cryptsetup open /dev/sda4 main
|
|
|
|
# Format it to ext4:
|
|
mkfs.ext4 /dev/mapper/main
|
|
```
|
|
|
|
### Install and configure Debian
|
|
|
|
* Mount the partitions
|
|
|
|
```bash
|
|
# Decrypt the main partition (if not already done):
|
|
cryptsetup open /dev/sda4 main
|
|
# mount it:
|
|
mount /dev/mapper/main /mnt
|
|
# Mount the boot partition:
|
|
mkdir /mnt/boot
|
|
mount /dev/sda3 /mnt/boot
|
|
```
|
|
|
|
* Bootstrap latest stable Debian into mounted partitions
|
|
|
|
```bash
|
|
debootstrap --arch amd64 stable /mnt http://ftp.fr.debian.org/debian/
|
|
```
|
|
|
|
* Mount system partitions
|
|
|
|
```bash
|
|
mount -o bind /dev /mnt/dev
|
|
mount -t proc proc /mnt/proc
|
|
mount -t sysfs sys /mnt/sys
|
|
mount -t devpts devpts /mnt/dev/pts
|
|
```
|
|
|
|
* Chroot
|
|
|
|
chroot /mnt /bin/bash
|
|
|
|
* Fill out `crypttab` and `fstab` (`UUID` is the output of above `cryptsetup luksDump`)
|
|
|
|
`/etc/crypttab`
|
|
|
|
```bash
|
|
cat << EOF > /etc/crypttab
|
|
# <name> <device> <password> <options>
|
|
main UUID=09762476-ba7c-4732-8856-44a716c23339 none luks
|
|
swap /dev/sda2 /dev/urandom swap,noearly,cipher=aes-xts-plain64,size=512
|
|
EOF
|
|
```
|
|
|
|
`/etc/fstab`
|
|
|
|
```bash
|
|
cat << EOF > /etc/fstab
|
|
# <filesystem> <dir> <type> <options> <dump> <pass>
|
|
/dev/mapper/main / ext4 errors=remount-ro 0 1
|
|
/dev/sda3 /boot ext4 defaults 0 2
|
|
/dev/mapper/swap none swap sw 0 0
|
|
EOF
|
|
```
|
|
|
|
* Do the `/proc/mounts` -> `/etc/mtab` symlink
|
|
|
|
```bash
|
|
ln -s /proc/mounts /etc/mtab
|
|
```
|
|
|
|
Why? [Linux From Stratch](http://archive.linuxfromscratch.org/lfs-museum/3.3/LFS-BOOK-3.3-HTML/chapter06/mtablink.html) and [our guide on OpsBlog](https://opsblog.net/posts/full-disk-encrypted-ubuntu-kimsufi-sever/) both say it's needed.
|
|
|
|
* Choose a hostname & DNS domain
|
|
|
|
hammerhead & hammerhead.luxeylab.net
|
|
|
|
* Fill in network-related files
|
|
|
|
`/etc/sysctl.d/10-ipv6`
|
|
|
|
Disable IPv6 auto-configuration
|
|
|
|
```bash
|
|
cat << EOF > /etc/sysctl.d/10-ipv6
|
|
net.ipv6.conf.all.autoconf=0
|
|
net.ipv6.conf.all.accept_ra=0
|
|
EOF
|
|
```
|
|
|
|
|
|
`/etc/network/interfaces`
|
|
|
|
Beware of your ethernet interface name! It's only after failing with `eth0` that the boot logs informed me that the iface name was `eno1`.
|
|
|
|
```bash
|
|
cat << EOF > /etc/network/interfaces
|
|
######################################################################
|
|
# /etc/network/interfaces -- configuration file for ifup(8), ifdown(8)
|
|
# See the interfaces(5) manpage for information on what options are
|
|
# available.
|
|
######################################################################
|
|
|
|
# loopback interface
|
|
auto lo
|
|
iface lo inet loopback
|
|
|
|
# eno1
|
|
auto eno1
|
|
allow-hotplug eno1
|
|
|
|
iface eno1 inet static
|
|
address 5.135.179.11
|
|
netmask 255.255.255.0
|
|
gateway 5.135.179.254
|
|
|
|
iface eno1 inet6 static
|
|
address 2001:41d0:8:ba0b::1
|
|
netmask 128
|
|
|
|
post-up /sbin/ip -f inet6 route add 2001:41d0:8:baff:ff:ff:ff:ff dev eno1
|
|
post-up /sbin/ip -f inet6 route add default via 2001:41d0:8:baff:ff:ff:ff:ff
|
|
pre-down /sbin/ip -f inet6 route del 2001:41d0:8:baff:ff:ff:ff:ff dev eno1
|
|
pre-down /sbin/ip -f inet6 route del default via 2001:41d0:8:baff:ff:ff:ff:ff
|
|
EOF
|
|
```
|
|
|
|
[This OVH IPv6 guide](https://docs.ovh.com/gb/en/dedicated/network-ipv6/) might help you out for the IPv6 part.
|
|
|
|
`/etc/resolv.conf`
|
|
|
|
```bash
|
|
cat << EOF > /etc/resolv.conf
|
|
# OVH public DNS
|
|
nameserver 213.186.33.99
|
|
# https://servers.opennicproject.org/edit.php?srv=ns2.he.de.dns.opennic.glue
|
|
nameserver 172.104.136.243
|
|
EOF
|
|
```
|
|
|
|
`/etc/hosts`
|
|
|
|
```bash
|
|
cat << EOF > /etc/hosts
|
|
127.0.0.1 localhost
|
|
127.0.1.1 hammerhead hammerhead.luxeylab.net
|
|
|
|
# The following lines are desirable for IPv6 capable hosts
|
|
::1 localhost ip6-localhost ip6-loopback
|
|
fe00::0 ip6-localnet
|
|
ff00::0 ip6-mcastprefix
|
|
ff02::1 ip6-allnodes
|
|
ff02::2 ip6-allrouters
|
|
ff02::3 ip6-allhosts
|
|
|
|
213.186.33.116 ws.ovh.com
|
|
198.245.48.4 ws.ovh.ca
|
|
5.135.179.11 hammerhead hammerhead.luxeylab.net
|
|
EOF
|
|
```
|
|
|
|
`/etc/hostname`
|
|
|
|
```bash
|
|
echo "hammerhead" > /etc/hostname
|
|
```
|
|
|
|
`/etc/timezone`
|
|
|
|
```bash
|
|
dpkg-reconfigure tzdata
|
|
```
|
|
|
|
* Update APT repositories in `/etc/apt/sources.list`
|
|
|
|
```bash
|
|
cat << EOF > /etc/apt/sources.list
|
|
deb http://ftp.fr.debian.org/debian buster main
|
|
deb-src http://ftp.fr.debian.org/debian buster main
|
|
|
|
deb http://ftp.fr.debian.org/debian-security/ buster/updates main
|
|
deb-src http://ftp.fr.debian.org/debian-security/ buster/updates main
|
|
|
|
deb http://ftp.fr.debian.org/debian buster-updates main
|
|
deb-src http://ftp.fr.debian.org/debian buster-updates main
|
|
EOF
|
|
```
|
|
|
|
* Configure locales & keyboard
|
|
|
|
```bash
|
|
# Refresh packages list
|
|
apt update
|
|
# Install & configure locales
|
|
apt install locales && dpkg-reconfigure locales
|
|
# Install & configure keyboard
|
|
apt install console-setup console-data && dpkg-reconfigure keyboard-configuration
|
|
```
|
|
|
|
* Pick up a kernel & install it
|
|
|
|
```bash
|
|
apt-cache search linux-image
|
|
# I selected the meta-package `linux-image-amd64` which is the latest
|
|
apt install linux-image-amd64 linux-headers-amd64
|
|
```
|
|
|
|
* Install additional necessary software
|
|
|
|
```bash
|
|
apt install cryptsetup dropbear grub-pc man-db ssh
|
|
```
|
|
|
|
Because we use a GPT table layout but no UEFI, we install `grub-pc` and not `grub-efi-amd64`.
|
|
|
|
Do think about installing `bash-completion` and `ufw` someday.
|
|
|
|
|
|
* Set up SSH keys and the rest (where `<PUBLIC_SSH_KEY>` is your client SSH public key)
|
|
|
|
```bash
|
|
mkdir /root/.ssh && chmod 600 /root/.ssh
|
|
echo "<PUBLIC_SSH_KEY>" > /root/.ssh/authorized_keys
|
|
echo "<PUBLIC_SSH_KEY>" > /etc/dropbear-initramfs/authorized_keys
|
|
```
|
|
|
|
* Configure dropbear-initramfs (SSH on boot)
|
|
|
|
```bash
|
|
sed -i 's/#DROPBEAR_OPTIONS=/DROPBEAR_OPTIONS=\"-p 2222 -c \/bin\/cryptroot-unlock\"/' /etc/dropbear-initramfs/config
|
|
```
|
|
|
|
|
|
This changes the SSH listen post to 2222, and enforces that the only command run from `dropbear-initramfs` is `cryptroot-unlock`.
|
|
|
|
* Configure sshd custom listen port (SSH after boot)
|
|
|
|
```bash
|
|
sed -i 's/#Port 22/Port 2223/' /etc/ssh/sshd_config
|
|
```
|
|
|
|
* [Optional] Authorize root password login
|
|
|
|
```bash
|
|
# Remove -s (disable password login) from dropbear-initramfs
|
|
sed -i 's/local flags=\"Fs\"/local flags=\"F\"/' /usr/share/initramfs-tools/scripts/init-premount/dropbear
|
|
```
|
|
|
|
* Update GRUB and initramfs
|
|
|
|
```bash
|
|
update-grub && update-initramfs -u
|
|
```
|
|
|
|
* Clean up before leaving
|
|
|
|
```bash
|
|
exit
|
|
umount /mnt/{boot,dev/pts,dev,proc,sys}
|
|
umount /mnt
|
|
cryptsetup luksClose main
|
|
```
|
|
|
|
### Boot and log into the server
|
|
|
|
* I configured my laptop's `~/.ssh/config` like so:
|
|
|
|
```
|
|
Host hammerhead-decrypt
|
|
User root
|
|
Hostname <SERVER_URL_OR_IP>
|
|
Port 2222
|
|
IdentityFile <PRIVATE_SSH_KEY_PATH>
|
|
# Prevents signatures mismatch
|
|
UserKnownHostsFile ~/.ssh/known_hosts_hammerhead-decrypt
|
|
Host hammerhead
|
|
User root
|
|
Hostname <SERVER_URL_OR_IP>
|
|
Port 2223
|
|
IdentityFile <PRIVATE_SSH_KEY_PATH>
|
|
```
|
|
|
|
* And here is how I connect to the server:
|
|
|
|
```bash
|
|
laptop$ ssh hammerhead-decrypt
|
|
Please unlock disk main: <PASSWORD>
|
|
# [...]
|
|
Connection to <SERVER_URL_OR_IP> closed.
|
|
laptop$ ssh hammerhead
|
|
# [...]
|
|
root@hamerhead:~# echo A winner is you!
|
|
A winner is you!
|
|
```
|
|
|
|
|
|
### Setup automated decryption from a remote
|
|
|
|
It is desirable to have a daemon running on a remote server, to automatically decrypt the drive when the encrypted server reboots without warning.
|
|
|
|
The remote server is called a *key escrow*. One must be particularly careful about the escrow's security, since it holds the decryption keys for our server.
|
|
|
|
Trinity recommends [Tang](https://github.com/latchset/tang) and [Clevis](https://github.com/latchset/clevis). |