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luks cryptsetup linux ubuntu harddisk encryption

Header Backup

https://www.lisenet.com/2013/luks-add-keys-backup-and-restore-volume-header/

cryptsetup luksHeaderBackup /dev/md1  --header-backup-file /root/luks-header-md1.backup

Change a password

  • cryptsetup luksDump /dev/sda5
    • Key Slot 0: ENABLED
      Key Slot 1: DISABLED
      ...

Add new password as second one (1) and then delete first one (0)

  • cryptsetup luksAddKey --key-slot 1 /dev/sda5
  • cryptsetup luksDump /dev/sda5
  • cryptsetup luksRemoveKey --key-slot 0 /dev/sda5
    • WARNING: IF YOU REMOVE THE LAST KEY VOLUME WILL BE INACCESSIBLE!

For automated script usage:

  • export $OLD_LUKS_KEY=foo

  • export $LUKS_KEY=bar

  • echo -e "$OLD_LUKS_KEY\n$LUKS_KEY\n$LUKS_KEY" | cryptsetup luksAddKey --key-slot=1 /dev/sda5

  • echo -e "$OLD_LUKS_KEY" | cryptsetup luksRemoveKey --key-slot 0 /dev/sda5

  • unset $OLD_LUKS_KEY

  • unset $LUKS_KEY

Encrypt external or separate harddisk

Example for /dev/sdd (use "blkid" to find the right harddisk)

  • Delete partition table (make it like factory new)
    • dd if=/dev/zero of=/dev/sdd bs=512 count=1
      • or
    • wipefs --all /dev/sdb
  • cfdisk /dev/sdd
    • gpt
    • create linux partition, full space
    • or
  • sgdisk --clear /dev/sdb
  • sgdisk --new=1 --change-name 1:"my_partition" /dev/sdb
  • cryptsetup luksFormat --cipher aes-xts-plain64 --verify-passphrase --key-size 256 /dev/sdd1

Open encrypted harddisk

 

Close encrypted harddisk

  • cryptsetup luksClose my-external-disk

 

 

Create filesystem on opened harddisk

 

 

For example "ext4"

  • mkfs.ext4 /dev/mapper/my-external-disk
  • mount /dev/mapper/my-external-disk /mnt

Auto Decrypt Harddisk upon Boot

  • mkdir /root/.keyfiles
  • dd if=/dev/urandom of=/root/.keyfiles/my-external-disk.key bs=1024 count=4
  • chmod 400 /root/.keyfiles/my-external-disk.key
  • cryptsetup luksAddKey /dev/sdd1 /root/.keyfiles/my-external-disk.key
  • blkid -> note uuid
  • vi /etc/crypttab

    • my-external-disk_crypt UUID=26d5247e-4358-4089-a4cc-f2f9c37b05be /root/.keyfiles/my-external-disk.key luks,discard

  • mkdir /my-external-disk

  • vi /etc/fstab

    • # my-external-disk

      /dev/mapper/my-external-disk_crypt /my-external-disk ext4 defaults,noatime 0 2

Auto Decrypt Harddisk on a headless, encrypted Server via SSH

Szenario:

my-encrypted-server: A headless server with an encrypted harddisk "my-external-disk"

my-unlock-server: A secure secondary server which provides the decryption key

@my-encrypted-server

  • create ssh key
    • ssh-keygen -t rsa -b 4096 -o -a 64
    • cat ~/.ssh/id_rsa.pub
      • copy to clipboard

@my-unlock-server

  • adduser unlock-luks
  • vi /home/unlock-luks/.ssh/authorized_keys
    • paste key from above
    • prepend to the key; this restricts access to this specific ip, and to this specific command
      • restrict,from=111.222.333.444,command="cat ~/.keyfiles/my-encrypted-server_my-external-disk.key"
  • sudo -u unlock-luks mkdir /home/unlock-luks/.keyfiles
  • sudo -u unlock-luks dd if=/dev/urandom of=/home/unlock-luks/.keyfiles/my-encrypted-server_my-external-disk.key bs=1024 count=4
  • chmod o-rwx /home/unlock-luks/.keyfiles -R

@my-encrypted-server

  • blkid
    • /dev/sdd1: UUID="204c6379-f0ca-43ff-a0dd-f862528b5931" TYPE="crypto_LUKS" PARTUUID="411379ab-0b35-4f4c-9a51-bfe890c6f261"
  • sshfs unlock-luks@my-unlock-server:/home/unlock-luks/.keyfiles /mnt
  • cryptsetup luksAddKey /dev/sdd1 /mnt/my-encrypted-server_my-external-disk.key
  • cryptsetup luksClose my-external-disk
  • umount /mnt
  • #!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.

ssh unlock-luks@my-unlock-server | cryptsetup luksOpen /dev/sdd1 my-external-disk -d -
mount /dev/mapper/my-external-disk /my-external-disk

exit 0
    •  
  • vi /etc/rc.local
  • chmod 700 /etc/rc.local

Get crypt partition/device for root filesystem

  • lsblk --ascii --output='NAME,FSTYPE,MOUNTPOINT' | grep '/$' --before-context=2 | grep crypto_LUKS | tail --lines=1 | cut --characters='3-' | cut --delimiter=' ' --fields=1

Remove Luks Swap

  • swapoff -a
  • umount /dev/mapper/crypt-swap_1
  • vi /etc/fstab
    • remove or comment out swap entry
  • lvremove /dev/mapper/crypt-swap_1
  • vi /etc/initramfs-tools/conf.d/resume
    • RESUME=
  • update-initramfs -u

TODO: checkout "cryptsetup remove cryptswap1"

Mount encrypted kvm qcow2 image

  • modprobe nbd max_part=8
  • qemu-nbd --connect=/dev/nbd0 vaultfish-root.qcow2
  • fdisk -l /dev/nbd0
    • /dev/nbd0p1 *       2048  1499135  1497088  731M 83 Linux
      /dev/nbd0p2      1501182 20969471 19468290  9.3G  5 Extended
      /dev/nbd0p5      1501184 20969471 19468288  9.3G 83 Linux
  • cryptsetup luksDump /dev/nbd0p5 foo
  • blkid
    • ...

      /dev/nbd0p1: UUID="f852180e-dc37-4767-ab95-aabde55cfd1a" TYPE="ext4" PARTUUID="2ee1b789-01"
      /dev/nbd0p5: UUID="4406d63e-ab16-4dca-b913-1f6cd7edc040" TYPE="crypto_LUKS" PARTUUID="2ee1b789-05"
      /dev/mapper/foo: UUID="ihhKBo-v3ML-BTZI-c1Q7-yuEW-LxIR-9QLVFH" TYPE="LVM2_member"
      /dev/mapper/crypt-root: UUID="d3f17767-d65e-4ace-b1e2-bc32a0c54dc6" TYPE="ext4"
      ...

  • mount /dev/mapper/crypt-root /mnt
  • ...
  • umount /mnt
  • qemu-nbd --disconnect /dev/nbd0