LUKS

LUKS encryption

Getting Started

See Archwiki: dm-crypt/Device encryption.

Encrypting a device

• Setup encryption

cryptsetup -v --type luks1 --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>
# E.g.
# mkfs.ext4 /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

Notes

• 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.

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

Mounting

# Open the encrypted drive
cryptsetup open <device> <name>
# Mount your partition
mount -t <fstype> /dev/mapper/<name> <mountlocation>

Unmounting

# Unmount your partition
umount <mountlocation>
# Close the decrypted drive
cryptsetup close <name>

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