Setting up a laptop

This material is work-in-progress ... Do not follow instructions here until this notice is removed. (Last edited by Orson Teodoro on 9 Mar 2018.)

Creating a secured laptop is a fun project. I've created this in my Gentoo days but could attempt to do it the Alpine way. For this project we take in consideration ways to extend battery life. It covers tools and daemons that are must haves for a laptop setup.

Guide features

• Deniable full disk encryption
• Two factor authentication (physical (USB key), mind)
• Encrypted swap and hibernation
• Encrypted home on top of encrypted drive
• Memory sanitation
• Dynamic power modes
• Feature keys support

Rubberhose Attack

Just a reminder that all attacks are subjected to the Rubberhose Attack dilemma, you either give up your encryption keys or be tortured with a rubberhose with the possibly of death. See Wikipedia article.

Why full disk?

The full disk encryption provides sort of some plausible deniability or a valid alibi that you didn't encrypt it. Is the drive just random noise, broken, or is it really encrypted? But, cryptsetup does leave plaintext marking or some hints that it has been encrypted when using luks/luks2 mode if a detached with option --header <path> is not presented.[1][2] To gain credibility that we didn't really do the encryption, you have to wipe the +3 MiB region based on the number of key slots used.

It is possible to erase and restore the header. This presents an opportunity to improve obfuscation. When you pull out the USB key, it should erase the header but store it on the USB key atomically as in completely. If you plug in the USB key, it will restore back the header. cryptsetup has luks actions luksHeaderBackup and luksHeaderRestore to do this.

Starting at the beginning

Grab a USB thumb drive with Alpine. Set it up as usual but don't let it touch your drive yet. Then, install all the tools into memory ramdisk but not in the hard drive yet. The hard drive will be obliterated.

Randomizing the drive with pseudorandom urandom entropy

The first part is to erase the drive with random noise but in practical time. There are many techniques to do this but should be done in one day or two minimum.

You can use shred or dd to accomplish this depending on your needs and the availability of entropy. Some techniques take longer. Cryptologist Bruce Schneier recommended 7 times with specified pattern. See Wikipedia Article. For practical purposes, we just do it random in one pass.

To list the drives on the system do fdisk -l.

IMPORTANT: make sure you wipe the right specific drive.

To wipe the disk with random entropy do:

 dd if=/dev/urandom of=/dev/sda

Creating GPG keys

After you have scrambled the drive, you want to create your GPG keys. You will use these keys to set the password(s) for your cryptsetup-luks partitions. These keys should be stored on a USB thumb drive which will act as the boot partition and the USB key. The key should be a random 128 bit key wrapped in GPG and protected with a password.

If you are using x, you need to do sudo apk add pinentry-gtk to display password prompt properly for the next step.

 openssl rand -base64 128 | gpg --symmetric --cipher-algo aes --armor > /mnt/usb/db4777249eceea20f855bc948e54a786eac98e38bec0e8ccf459b7f096cdfc798154a430879e9c48ece373d706defccf

(Make sure your usb is mounted on /mnt/usb first.)

The long file name comes from openssl rand 48 -hex so that we enhance plausible deniability.

The first part will produce 128 random bytes in wrap it in base64. The random data will be piped to gpg which will wrap it in AES as ciphertext which again gets wrapped in base64 ascii armor. For every partition, you should create more gpg keys and store them in your USB thumb drives. After you have produced your gpg keys, you will then use them as a password for cryptsetup/luks.

You can replace aes above with the ones listed in gpg --version.

Full disk encryption with with cryptsetup-luks volumes

Installing cryptsetup

To install cryptsetup you need the package below

 apk add cryptsetup

Choosing ciphers

When you create your luks drives, you need to decide on the type of ciphers and hashing techniques to use. The ciphers that you want to use are ones are up to you, but it should be one that is hasn't been cracked yet or has not suffered a lot of cryptanalysis attacks. The ones that you might want to use is AES which is hardware accelerated in some Intel CPUs that have the AES-NI cpuflag which you can check by cat /proc/cpuinfo. Also consider the ciphers that are SIMD optimized such as serpent and twofish that are available in the Linux kernel. Also consider ciphers that are unpopular but known to be secure such as blowfish. If it is hardware accelerated, it will save battery life and minimize CPU usage.

Another advantage of using a public vetted cipher is that it provides confidence that it works.

Generally speaking, the swap partition should use a fast cipher.

Getting the available ciphers

 cryptsetup benchmark

The top set is associated with the hashing algorithms. The bottom set are the ciphers. Use the commands below but replace the cipher and/or hash algorithm with your preferences.

IMPORTANT: do not use sha1 as the hashing algorithm. It already has already been compromised.

General steps for cryptsetup

Original method with fdisk with no plausible deniability

In this method --type luks is implied which generates metadata.

If you want plausible deniability for luks, you need to pass --header <path> to all the luks commands, where <path> is a unix path like /mnt/usb/f6ecf2276181a79979540afccc22dd14bbb2bd0c1b299b571efee7ac831dad05a276836e42aac5f275807b29b71aae0d. (the random name comes from openssl rand -hex 48) The header is transferred to the external device (but no mention of the key slot area but ciphertext being transferred) in the man page. The information in that file should be obfuscated with encryption if there is plaintext or fingerprint in it just in case then decrypted when reused.

You need to install cfdisk if you prefer the interactive ncurses console method:

 apk add cfdisk

#	Step	Command
1	Use cfdisk to create partitions. Make two partitions--a system partition and a swap partition	cfdisk
2	Create and format the luks device	cryptsetup --cipher aes-cbc-essiv:sha256 --key-size 256 luksFormat /dev/sda1 /mnt/usb/key.gpg
3	Open the luks device	cryptsetup --key-file /mnt/usb/key.gpg luksOpen /dev/sda1 root
4	Format the decrypted drive with filesystem	mkfs.ext4 /dev/mapper/root
5	Create the mount point	mkdir -p /mnt/root
6	Mount the root partition	mount /dev/mapper/root /mnt/root
7	Create swap	cryptsetup -c blowfish -h sha256 -d /dev/urandom create swap /dev/sda2
8	Use swap	mkswap /dev/mapper/swap && swapon /dev/mapper/swap

Improved method with plausible deniability

This method requires lvm2. To install:

 apk add lvm2

#	Step	Command
1	Open the plain dm-crypt device generating no metadata	cryptsetup open --type plain --cipher aes-cbc-essiv:sha256 --key-size 256 --key-file /mnt/usb/key.gpg /dev/sda root
2	Physical volume create with LVM	pvcreate /dev/mapper/pvroot
3	Volume group create with LVM	vgcreate vgroot /dev/mapper/pvroot
4	Logical volume create the swap volume with LVM	lvcreate -L 4G vgroot -n swap
5	Logical volume create the root volume with LVM	lvcreate -L 2T vgroot -n root
6	Logical volume create the rescue volume with LVM	lvcreate -L 110M vgroot -n rescue
7	Format the root volume with filesystem	mkfs.ext4 /dev/mapper/vgroot-root
8	Format the swap volume and activate it	mkswap /dev/mapper/swap && swapon /dev/mapper/swap
9	Format the rescue volume with filesystem	mkfs.ext4 /dev/mapper/vgroot-rescue
10	Create mount point for root volume	mkdir -p /mnt/root
11	Mount the root volume	mount /dev/mapper/root /mnt/root

Partitioning scheme

#	Name	Mount point	Notes
1	swap		It should be the same size as your ram for x86_64. Rationale: it should contain the whole ram image.
2	root	/
3	rescue	/mnt/rescue	This should contain the Alpine image.

Configuring OpenRC dm-crypt and setting up fstab

You need to tell OpenRC init scripts to decrypt the volumes. See /etc/conf.d/dmcrypt.

You need to add the service to boot well because it needs to decrypt the root volume before OpenRC starts running commands from it. So you need to do:

 rc-update add dmcrypt boot

For luks:

Contents of /etc/conf.d/dmcrypt

target=root source='/dev/sda1' key='/mnt/usb/db4777249eceea20f855bc948e54a786eac98e38bec0e8ccf459b7f096cdfc798154a430879e9c48ece373d706defccf' swap=crypt-swap source='/dev/hda2'

For plain dm-crypt:

Contents of /etc/conf.d/dmcrypt

target=root source='/dev/hda' key='/mnt/usb/db4777249eceea20f855bc948e54a786eac98e38bec0e8ccf459b7f096cdfc798154a430879e9c48ece373d706defccf'

dm-crypt will just mount the encrypted plain dm-crypt drive or the luks partition. What you need to do next is set up fstab located at /etc/fstab. Examples are shown below.

Contents of /etc/fstab

/dev/sdb /boot ext4 defaults 0 0 /dev/mapper/root / ext4 defaults 0 1 /dev/mapper/swap none swap sw 0 0

To mount lvm volumes with fstab:

Contents of /etc/fstab

/dev/sdb /boot ext4 defaults 0 0 /dev/mapper/vgroot-lvroot / ext4 defaults 0 1 /dev/mapper/vgroot-lvswap none swap sw 0 0

How to recover from a bad setup

Many times you will not get it right perfectly the first try. To recover from this situation, all you need to do to resume back before the event where you messed up. What you need to do is reopen the plain dm-crypt drive or the luks drive and then remount everything back.

To recover from luks:

 cryptsetup --key-file /mnt/usb/key.gpg luksOpen /dev/sda1 root
 mkdir -p /mnt/root
 mount /dev/mapper/root /mnt/root

To recover from the plain dm-crypt:

 cryptsetup open --type plain --cipher aes-cbc-essiv:sha256 --key-size 256 --key-file /mnt/usb/key.gpg /dev/sda root
 lvchange -ay vgroot/root
 mkdir -p /mnt/root
 mount /dev/vgroot/root /mnt/root

Next step: Full blown Alpine installation

You will then install Alpine using the steps:

Install the bootloader in the USB thumb drive

To install grub, you need to install grub on the ramdisk first on the host.

 apk add grub

To get a list of partitions

 fdisk -l

Mount the boot partition in /boot

 mount /dev/sdb /boot

Make changes to grub's configuration

 nano /boot/grub/grub.cfg

Install it to your USB thumb drive

 grub-install /dev/sdb

Hacking mkinitfs

You may want to hack the mkinitfs init script and rebuild the package depending on what methods you use. You could possibly have a complex way to hide your GPG keys (again enhancing plausible deniability) with steganography or extend it with three-factor authentication which adds biometrics along side with mind and physical.

See https://github.com/alpinelinux/mkinitfs/tree/master .

Home mounting with eCryptfs

We use eCryptfs to encrypt home. The rationale for having another encrypted file system is that if you leave your laptop unattended on break or accidentally leave your USB key in, your data will not be accessible. When you log off due to inactivity, your home directory will be unmounted and encrypted. eCryptfs will encrypt/decrypt the filename and the contents and will sit on top of ext4 which sits on top of luks.

To install ecryptfs-utils:

 sudo apk add ecryptfs-utils

You need to write a custom script that does the following:

 * kill all running processes associated with your user account
 * auto logoff terminals
 * for the last terminal closed including all idle xservers, unmount your user home
 * (optional) use smem to wipe all your plaintext private data in memory after all closed programs in case of cold boot attack

This does only one factor authentication with just the password and the USB key inside. You need to reconfigure pam with the pam_usb.so which is not in Alpine aports.

Locking it down

Many times you will leave your laptop behind with people you trust. The following tools will help lock down the system.

physlock

This will auto lock the tty and when you return will prompt for password.

To install physlock:

 sudo apk add physlock

It is currently bugged. See [3]. physlock likely doesn't do two-factor authentication but it should.

You need to create custom script that will monitor idle time in TTY then call physlock. You load this script when you log on.

xscreensaver

This will lock you out of xserver

To install xscreensaver:

 sudo apk add xscreensaver

USB key udev rule

You need to add a new udev rule that will suspend-to-ram or hibernate and log off once you pull the USB key. When you come back on, you should do 2 factor authentication to restore back everything. Hibernation and suspend-to-ram might mitigate cold-boot attack (but unlikely see notes at the bottom of the page) to extract plaintext private data and encryption keys in memory.

To find out the details of your USB do:

 udevadm monitor --udev -p

The output should look like:

UDEV  [181762.722853] add      /devices/pci0000:00/0000:00:13.2/usb2/2-5/2-5:1.0/host6/target6:0:0/6:0:0:0/block/sdc (block)
ACTION=add
DEVLINKS=/dev/disk/by-id/usb-Kingston_MSFT_NORB_MSFTLAKDA300EB3021790009-0:0 /dev/disk/by-path/pci-0000:00:13.2-usb-0:5:1.0-scsi-0:0:0:0 /dev/disk/by-uuid/5A96-03E4
DEVNAME=/dev/sdc
DEVPATH=/devices/pci0000:00/0000:00:13.2/usb2/2-5/2-5:1.0/host6/target6:0:0/6:0:0:0/block/sdc
DEVTYPE=disk
ID_BUS=usb
ID_FS_TYPE=vfat
ID_FS_USAGE=filesystem
ID_FS_UUID=5A96-03E4
ID_FS_UUID_ENC=5A96-03E4
ID_FS_VERSION=FAT32
ID_INSTANCE=0:0
ID_MODEL=MSFT_NORB
ID_MODEL_ENC=MSFT\x20NORB\x20\x20\x20\x20\x20\x20\x20
ID_MODEL_ID=1645
ID_PATH=pci-0000:00:13.2-usb-0:5:1.0-scsi-0:0:0:0
ID_PATH_TAG=pci-0000_00_13_2-usb-0_5_1_0-scsi-0_0_0_0
ID_REVISION=PMAP
ID_SERIAL=Kingston_MSFT_NORB_MSFTLAKDA300EB3021790009-0:0
ID_SERIAL_SHORT=MSFTLAKDA300EB3021790009
ID_TYPE=disk
ID_USB_DRIVER=usb-storage
ID_USB_INTERFACES=:080650:
ID_USB_INTERFACE_NUM=00
ID_VENDOR=Kingston
ID_VENDOR_ENC=Kingston
ID_VENDOR_ID=0951
MAJOR=8
MINOR=32
SEQNUM=2027
SUBSYSTEM=block
USEC_INITIALIZED=1762722168

You want to extract the ID_SERIAL_SHORT=MSFTLAKDA300EB3021790009 or whatever is associated with your USB thumb drive.

You need pm-utils for ps-suspend. So to install it do:

 sudo apk add pm-utils

You will create a udev rules so that when you pull out the USB, it will suspend-to-ram or you can use your own script. To do that create a file with the following contents:

Contents of /etc/udev/rules.d/50-usb-thumb-drive.rules

ACTION=="remove", SUBSYSTEM=="usb", ENV{ID_SERIAL_SHORT}=="MSFTLAKDA300EB3021790009", RUN+="/usr/sbin/pm-suspend"

Extending battery life

ACPI

ACPI is a good daemon to use to execute certain scripts when laptop events are triggered.

To install ACPI do:

 apk add acpi

The events to pay attention to are:

Event	ACPI Event	What your script should do
lid close		log off ttys and suspend-to-ram. ALSA should either set the volume to 0 for the sound card or the sound driver be unloaded. It might be a good idea to kill or mute any music or movie players if the sound loops loudly after lid open.
lid open		lock all ttys and all xservers should be locked, possibly reinitialize ALSA and the sound system.
tapped power button		lock all ttys and suspend-to-ram
held power button		hibernate
unplugged power		should switch to 'conservative' cpufreq governor at above 25% power ; 'powersave' governor at 25%. set hdparam spindown rate lower.
plugged power		should switch to 'performance' governor. disable hdparam spindown.

The purpose of the power governor is to regulate the running frequency (GHz) of the processor.

Certain event handlers are are managed through laptop-mode-tools. If you don't want the dependency, then you could write ACPI handler scripts.

acpi_listen can be used to retrieve the event name.

TODO: put scripts below

Adjusting the backlight dynamically

The backlight may be controlled using sysfs. The setting is a descendant of /sys/class/backlight/. The feature may allow you to echo a value to it. Use trial and error to discover the values.

The adjustment of the backlight should be function of battery life. So if it is like 33% battery life, you want to run it near lowest settings but readable. For 50 percent battery energy maybe 40% light. For 90% battery maybe 75% light.

hdparm

To install hdparam do:

 sudo apk add hdparm

The settings that laptop-mode-tools messes with is the -S or the spindown timeout. It was also hinted that acoustic setting -M is associated with the speed meaning that louder is faster and quieter is slower which could contribute to the amount of energy used or reduced.

Again you want something like laptop-mode-tools or ACPI to dynamically adjust the settings based on ACPI events.

laptop-mode-tools

This is currently not in aports but worthy mentioning. It should really be packaged. This is a set of scripts to define a power policies. You can manage all the settings in one place here like the hard drive idle spindown time, CPU governor control, dynamic LCD backlight behavior based on running on battery or AC power supply.

cpufreqd

This is a useful daemon to regulating power.

To install cpufreqd do:

 sudo apk add cpufreqd

Make sure you add the service

 sudo rc-update add cpufreqd

Hacking the kernel

You should refer to the Custom Kernel page for details.

Hibernation

See Hibernation to prevent data loss.

WiFi management

Since you are using WiFi, you need a better WiFi management to quickly find open access WiFi access points. We don't have all day to debug complexities of WiFi settings while away from home.

To install NetworkManager do:

 sudo apk add networkmanager

To find WiFi access points use the nmtui ncurses interface.

You also need other programs so install them as well:

 apk add wpa-supplicant dhcpcd chrony macchanger wireless-tools iputils

What these programs do:

• wpa-supplicant -- for WPA encryption
• dhcpcd -- for getting a dynamic IP address
• chrony -- for fixing the time with the atomic clock
• wireless-tools -- for additional information
• macchanger -- for protecting against WiFi access discrimination or increased anonymity. (optional)
• iputils -- for the ping command (optional)

You also need to add those services:

 rc-update add chrony
 rc-update add wpa-supplicant
 rc-update add dhcpcd
 rc-update add networkmanager

To start the services manually (or just reboot):

 /etc/init.d/chrony start
 /etc/init.d/wpa-supplicant start
 /etc/init.d/dhcpcd start
 /etc/init.d networkmanager start

Additional tools

actkbd

To control the sound with fn function keys, you need this daemon. It is currently not in aports. You could override the design and meaning of those keys with your own scripts and utilities. This daemon gives you that freedom.

If your laptop contains a brightness key, you want to set that up with this program. See also Adjusting the backlight dynamically.

secure-delete

Want to prevent cold-boot attack or decrypted keys in memory falling in the wrong hands? This maybe could work who knows?

To install secure-delete do:

 sudo apk add secure-delete

smem only works for unused ram.[4] If you use the vanilla kernel, this may work. If you use grsecurity, it will automatically sanitize memory [unconfirmed if enabled] when the memory page is freed.[5]

Close all important programs then call smem.

You call smem in your shutdown script or auto-logoff script.

You can call create a OpenRC shutdown script to run smem when most programs and services are closed. This will erase all your sensitive plaintext private data just in case.

You may want to create a wrapper script to call smem after you run your program closes.

Sharing presentations over HDMI

If you want to use your laptop to share presentation over HDMI connection, you need libxinerama and xrandr.

To install libxinerama and xrandr do:

 sudo apk add libxinerama xrandr

Notes

If you lose or break your USB key, that is it and you cannot decrypt your drive. It would be wise to make a backup of it.

I don't know if suspend-to-ram or hibernate sufficiently clear the AES encryption keys off ram in those phases which would invite a cold boot attack. This has been covered by the TRESOR kernel patch.[6] This patch hasn't been updated since the 4.x kernel series.[7]