LUKS

LUKS encryption

Getting Started

See Archwiki: dm-crypt/Device encryption.

Install cryptsetup

sudo apt install cryptsetup

Encrypting a device

• Setup encryption

cryptsetup -v --type luks2 --cipher aes-xts-plain64 --key-size 512 --hash sha512 \
           --iter-time 5000 --use-urandom --verify-passphrase luksFormat "${DEVICE}"

• Open encrypted drive

cryptsetup open "${DEVICE}" "${NAME}"

• Create a partition

mkfs.fstype "/dev/mapper/${NAME}"
# mkfs.btrfs /dev/mapper/luksdrive1

• Securely wipe the unused portion of the drive
  • Do this to prevent cryptographic attacks and to overwrite existing data on the drive

dd if=/dev/zero of=<file_somewhere> status=progress
# Delete the file afterwards

Mounting

# Open the encrypted drive
cryptsetup open "${DEVICE}" "${NAME}"
# Mount your partition
mount -t btrfs /dev/mapper/${NAME} "${MOUNT_LOCATION}"

Unmounting

# Unmount your partition
umount "${MOUNT_LOCATION}"
# Close the decrypted drive
cryptsetup close ${NAME}

Encrpytion Options

• You can see defaults using cryptsetup --help.
• --type options
  • luks defaults to luks1 on cryptsetup < 2.1.0, luks2 on cryptsetup >= 2.1.0
  • luks1 is the standard version of LUKS.
  • luks2 is a new version released in Dec 2017. Older versions of Grub (before 2.06 or June 2020) do not support booting from LUKS2.
  • plain is dm-crypt plain mode. Avoid this unless you know what you're doing.
  • loopaes Avoid this as well.
  • tcrypt Use this for mounting older truecrypt volumes.

• --iter-time dynamically determines the number of iterations used to hash your password. The number of iterations is determined when creating the luks key. E.g. 5000 means hash for 5 seconds worth of iterations on your particular CPU. You can see the number of iterations for each key with cryptsetup luksDump <device>.

defaults

defaults on Ubuntu 18.04

Default compiled-in device cipher parameters:
	loop-AES: aes, Key 256 bits
	plain: aes-cbc-essiv:sha256, Key: 256 bits, Password hashing: ripemd160
	LUKS1: aes-xts-plain64, Key: 256 bits, LUKS header hashing: sha256, RNG: /dev/urandom

Benchmark

cryptsetup benchmark

Example Output

# Tests are approximate using memory only (no storage IO).
PBKDF2-sha1      1213629 iterations per second for 256-bit key
PBKDF2-sha256    1524093 iterations per second for 256-bit key
PBKDF2-sha512    1082121 iterations per second for 256-bit key
PBKDF2-ripemd160  648069 iterations per second for 256-bit key
PBKDF2-whirlpool  421453 iterations per second for 256-bit key
argon2i       4 iterations, 875179 memory, 4 parallel threads (CPUs) for 256-bit key (requested 2000 ms time)
argon2id      4 iterations, 889195 memory, 4 parallel threads (CPUs) for 256-bit key (requested 2000 ms time)
#     Algorithm |       Key |      Encryption |      Decryption
        aes-cbc        128b       542.7 MiB/s      2192.7 MiB/s
    serpent-cbc        128b        67.3 MiB/s       459.9 MiB/s
    twofish-cbc        128b       140.6 MiB/s       285.8 MiB/s
        aes-cbc        256b       405.3 MiB/s      1701.8 MiB/s
    serpent-cbc        256b        71.6 MiB/s       459.5 MiB/s
    twofish-cbc        256b       146.6 MiB/s       287.1 MiB/s
        aes-xts        256b      1421.6 MiB/s      1449.2 MiB/s
    serpent-xts        256b       455.9 MiB/s       444.0 MiB/s
    twofish-xts        256b       284.2 MiB/s       286.3 MiB/s
        aes-xts        512b      1187.2 MiB/s      1177.9 MiB/s
    serpent-xts        512b       454.7 MiB/s       446.1 MiB/s
    twofish-xts        512b       284.9 MiB/s       286.5 MiB/s

Adiantum

If you're running a device which does not support AES instructions (e.g. Raspberry Pi), you may be interested in Adiantum.
Adiantum is an encryption mode by Google which uses ChaCha12 for block encryption. It is included in Linux kernel v5.0.

Creation

cryptsetup -v --type luks2 --cipher xchacha12,aes-adiantum --sector-size 4096 \
           --key-size 256 --hash sha512 --iter-time 5000 --use-urandom \
           --verify-passphrase luksFormat <device>

Benchmark

cryptsetup benchmark -c xchacha12,aes-adiantum -s 512

Scripts

mount_drives.sh

#!/bin/bash

function mount_luks {
    local fstype=$1
    local device=$2
    local name=$3
    local mountpoint=$4
    if [ ! -b /dev/mapper/"$name" ]
    then
        sudo cryptsetup open "$device" "$name"
    fi
    sudo mkdir -p "$mountpoint"
    sudo mount -t $fstype /dev/mapper/"$name" "$mountpoint"
}

mount_luks ext4 /dev/disk/by-id/<drive> lukscrypt1 /media/lukscrypt1

unmount_drives.sh

#!/bin/bash

function unmount_luks {
    local name=$1
    local mountlocation=$2
    sudo umount "$mountlocation" && \
    sudo rm -r "$mountlocation"
    sudo cryptsetup close "$name"
}

unmount_luks lukscrypt1 /media/lukscrypt1

Resources

• nixCraft How To Linux Hard Disk Encryption With LUKS