privacy-guides/how-to-create-encrypted-paper-backup

How to create encrypted paper backup

Requirements

• Hardened Raspberry Pi 📦
• Raspberry Pi OS-compatible auto-focus HD USB webcam
• Adafruit PiTFT monitor (optional)
• macOS computer

Caveats

• When copy/pasting commands that start with $, strip out $ as this character is not part of the command
• When copy/pasting commands that start with cat << "EOF", select all lines at once (from cat << "EOF" to EOF inclusively) as they are part of the same (single) command

Setup guide

Step 1: log in to Raspberry Pi

Replace 10.0.1.248 with IP of Raspberry Pi.

ssh pi@10.0.1.248 -i ~/.ssh/pi

Step 2 (optional): install Adafruit PiTFT monitor drivers and disable console auto login

Install Adafruit PiTFT monitor drivers

Heads-up: don’t worry about PITFT Failed to disable unit: Unit file fbcp.service does not exist..

Heads-up: when asked to reboot, type n and press enter.

$ sudo apt update

$ sudo apt install -y git python3-pip

$ sudo pip3 install adafruit-python-shell click==7.0

$ git clone https://github.com/adafruit/Raspberry-Pi-Installer-Scripts.git

$ cd Raspberry-Pi-Installer-Scripts

$ sudo python3 adafruit-pitft.py --display=28c --rotation=90 --install-type=console

$ cd ~

$ rm -fr Raspberry-Pi-Installer-Scripts

Disable console auto login

Heads-up: when asked to reboot, select “No” and press enter.

sudo raspi-config

Select “System Options”, then “Boot / Auto Login”, then “Console” and finally “Finish”.

Step 3: configure keyboard keymap

Heads-up: following instructions are for Raspberry Pi keyboard (US model).

Heads-up: when asked to reboot, select “No” and press enter.

sudo raspi-config

Select “Localisation Options”, then “Keyboard”, then “Generic 105-key PC (intl.)”, then “Other”, then “English (US)”, then “English (US)”, then “The default for the keyboard layout”, then “No compose key” and finally “Finish”.

Step 4: install dependencies

$ sudo apt update

$ sudo apt install -y fim imagemagick zbar-tools

$ pip3 install mnemonic pillow qrcode --user

$ echo -e "export GPG_TTY=\"\$(tty)\"\nexport PATH=\$PATH:/home/pi/.local/bin" >> ~/.bashrc

$ source ~/.bashrc

Step 5 (optional): install screen and Trezor’s trezorcrl

Heads-up: we will likely use screen and trezorcrl command line utilities in the future and this guide is designed to configure a read-only Raspberry Pi.

$ sudo apt install -y screen

$ pip3 install attrs trezor --user

$ sudo curl https://data.trezor.io/udev/51-trezor.rules -o /etc/udev/rules.d/51-trezor.rules

Step 6: download create-seed.py (PGP signature, PGP public key)

sudo curl -o /usr/local/sbin/create-seed.py https://sunknudsen.com/static/media/privacy-guides/how-to-create-encrypted-paper-backup/create-seed.py

Step 7: download validate-seed.py (PGP signature, PGP public key)

sudo curl -o /usr/local/sbin/validate-seed.py https://sunknudsen.com/static/media/privacy-guides/how-to-create-encrypted-paper-backup/validate-seed.py

Step 8: download qr-backup.sh (PGP signature, PGP public key)

sudo curl -o /usr/local/sbin/qr-backup.sh https://sunknudsen.com/static/media/privacy-guides/how-to-create-encrypted-paper-backup/qr-backup.sh
sudo chmod +x /usr/local/sbin/qr-backup.sh

Step 9: download qr-restore.sh (PGP signature, PGP public key)

sudo curl -o /usr/local/sbin/qr-restore.sh https://sunknudsen.com/static/media/privacy-guides/how-to-create-encrypted-paper-backup/qr-restore.sh
sudo chmod +x /usr/local/sbin/qr-restore.sh

Step 10: download qr-clone.sh (PGP signature, PGP public key)

sudo curl -o /usr/local/sbin/qr-clone.sh https://sunknudsen.com/static/media/privacy-guides/how-to-create-encrypted-paper-backup/qr-clone.sh
sudo chmod +x /usr/local/sbin/qr-clone.sh

Step 11: download secure-erase.sh (PGP signature, PGP public key)

sudo curl -o /usr/local/sbin/secure-erase.sh https://sunknudsen.com/static/media/privacy-guides/how-to-create-encrypted-paper-backup/secure-erase.sh
sudo chmod +x /usr/local/sbin/secure-erase.sh

Step 12: make filesystem read-only

Heads-up: shout-out to Nico Kaiser for his amazing guide on how to configure a read-only Raspberry Pi.

Disable swap

sudo dphys-swapfile swapoff
sudo dphys-swapfile uninstall
sudo systemctl disable dphys-swapfile.service

Remove dphys-swapfile fake-hwclock and logrotate

sudo apt remove -y --purge dphys-swapfile fake-hwclock logrotate

Link /etc/console-setup to /tmp/console-setup

sudo mv /etc/console-setup /tmp/console-setup
sudo ln -s /tmp/console-setup /etc/console-setup

Link /etc/resolv.conf to /tmp/resolv.conf

sudo mv /etc/resolv.conf /tmp/resolv.conf
sudo ln -s /tmp/resolv.conf /etc/resolv.conf

Link /home/pi/.gnupg to /tmp/pi/.gnupg

mkdir -m 700 /tmp/pi
mv /home/pi/.gnupg /tmp/pi/.gnupg
ln -s /tmp/pi/.gnupg /home/pi/.gnupg

Enable tmp.mount service

echo -e "D /tmp 1777 root root -\nD /tmp/console-setup 1700 root root -\nD /tmp/pi 1700 pi pi -\nD /tmp/pi/.gnupg 1700 pi pi -\nD /var/tmp 1777 root root -" | sudo tee /etc/tmpfiles.d/tmp.conf
sudo cp /usr/share/systemd/tmp.mount /etc/systemd/system/
sudo systemctl enable tmp.mount

Edit /boot/cmdline.txt

sudo cp /boot/cmdline.txt /boot/cmdline.txt.backup
sudo sed -i 's/fsck.repair=yes/fsck.repair=skip/' /boot/cmdline.txt
sudo sed -i '$ s/$/ fastboot noswap ro systemd.volatile=state/' /boot/cmdline.txt

Edit /etc/fstab

sudo cp /etc/fstab /etc/fstab.backup
sudo sed -i -e 's/vfat\s*defaults\s/vfat defaults,ro/' /etc/fstab
sudo sed -i -e 's/ext4\s*defaults,noatime\s/ext4 defaults,noatime,ro,noload/' /etc/fstab

Step 13: disable Wi-Fi (if not using ethernet)

echo "dtoverlay=disable-wifi" | sudo tee -a /boot/config.txt

Step 14: disable dhcpcd, networking and wpa_supplicant services and “fix” rfkill bug

$ sudo systemctl disable dhcpcd networking wpa_supplicant

$ sudo rm /etc/profile.d/wifi-check.sh

Step 15: delete macOS hidden files (if present)

sudo rm -fr /boot/.fseventsd /boot/.DS_Store /boot/.Spotlight-V100

Step 16: reboot

sudo systemctl reboot

WARNING: DO NOT CONNECT RASPBERRY PI TO NETWORK EVER AGAIN WITHOUT REINSTALLING RASPBERRY PI OS FIRST (DEVICE IS NOW "READ-ONLY" AND “COLD”).

Step 17 (optional): disable auto-mount of boot volume (on macOS)

Heads-up: done to prevent macOS from writing hidden files to boot volume which would invalidate stored SHA512 hash of micro SD card.

Insert micro SD card into macOS computer, run following and eject card.

volume_path="/Volumes/boot"
volume_uuid=$(diskutil info "$volume_path" | awk '/Volume UUID:/ { print $3 }')
echo "UUID=$volume_uuid none msdos rw,noauto" | sudo tee -a /etc/fstab

Step 18 (optional): compute SHA512 hash of micro SD card and store in password manager (on macOS)

Run diskutil list to find disk ID of micro SD card with “Raspberry Pi OS Lite” installed (disk2 in the following example).

$ diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                 Apple_APFS Container disk1         500.1 GB   disk0s2

/dev/disk1 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +500.1 GB   disk1
                                 Physical Store disk0s2
   1:                APFS Volume Macintosh HD - Data     340.9 GB   disk1s1
   2:                APFS Volume Preboot                 85.9 MB    disk1s2
   3:                APFS Volume Recovery                529.0 MB   disk1s3
   4:                APFS Volume VM                      3.2 GB     disk1s4
   5:                APFS Volume Macintosh HD            11.3 GB    disk1s5

/dev/disk2 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *15.9 GB    disk2
   1:             Windows_FAT_32 boot                    268.4 MB   disk2s1
   2:                      Linux                         15.7 GB    disk2s2

$ sudo diskutil unmountDisk /dev/diskn
Unmount of all volumes on disk2 was successful

$ sudo openssl dgst -sha512 /dev/rdiskn
SHA512(/dev/rdisk2)= 353af7e9bd78d7d98875f0e2a58da3d7cdfc494f2ab5474b2ab4a8fd212ac6a37c996d54f6c650838adb61e4b30801bcf1150081f6dbb51998cf33a74fa7f0fe

👍

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Usage guide

Create encrypted paper backup

Heads-up: use --bip39 to test secret against BIP39 word list.

$ qr-backup.sh --help
Usage: qr-backup.sh [options]

Options:
  --create-seed    create 24-word BIP39 seed
  --validate-seed  validate if secret is BIP39 seed
  -h, --help       display help for command

$ qr-backup.sh
Format USB flash drive? (y or n)?
y
mkfs.fat 4.1 (2017-01-24)
Type secret and press enter (again)
this is a test yo
-----BEGIN PGP MESSAGE-----

jA0ECQMKmFCBKHBUX8z/0kUBxi8eP7LRqP0WgOF+VgTMYuvix7AMxWR/TRM+zQk/
i9JLr52Odmxv23jEC/KfAUdigAqhs3/GJRtwWuC2IR5NzfBNvXM=
=xkQH
-----END PGP MESSAGE-----
SHA512 hash: 177cc163d89498b859ce06f6f2ac1cd2f9f493b848cdf08746bfb2f4a8bf958ebb45eb70f8f20141c12aa65387ee0545b7c0757cf8d6c808e2fa449fad0e986a
SHA512 short hash: 177cc163
Show SHA512 hash as QR code? (y or n)?
n
Done

Done

👍

The following image is now available on USB flash drive.

Restore encrypted paper backup

Heads-up: use --word-list to split secret into word list.

$ qr-restore.sh
Usage: qr-restore.sh [options]

Options:
  --word-list  split secret into word list
  -h, --help   display help for command

$ qr-restore.sh
Scan QR code…
-----BEGIN PGP MESSAGE-----

jA0ECQMKmFCBKHBUX8z/0kUBxi8eP7LRqP0WgOF+VgTMYuvix7AMxWR/TRM+zQk/
i9JLr52Odmxv23jEC/KfAUdigAqhs3/GJRtwWuC2IR5NzfBNvXM=
=xkQH
-----END PGP MESSAGE-----
SHA512 hash: 177cc163d89498b859ce06f6f2ac1cd2f9f493b848cdf08746bfb2f4a8bf958ebb45eb70f8f20141c12aa65387ee0545b7c0757cf8d6c808e2fa449fad0e986a
SHA512 short hash: 177cc163
Show secret? (y or n)?
y
gpg: AES256 encrypted data
gpg: encrypted with 1 passphrase
Secret: this is a test yo
Done

Done

👍

Clone encrypted paper backup

$ qr-clone.sh --help
Usage: qr-clone.sh [options]

Options:
  -h, --help  display help for command

$ qr-clone.sh
Scan QR code…
-----BEGIN PGP MESSAGE-----

jA0ECQMKmFCBKHBUX8z/0kUBxi8eP7LRqP0WgOF+VgTMYuvix7AMxWR/TRM+zQk/
i9JLr52Odmxv23jEC/KfAUdigAqhs3/GJRtwWuC2IR5NzfBNvXM=
=xkQH
-----END PGP MESSAGE-----
SHA512 hash: 177cc163d89498b859ce06f6f2ac1cd2f9f493b848cdf08746bfb2f4a8bf958ebb45eb70f8f20141c12aa65387ee0545b7c0757cf8d6c808e2fa449fad0e986a
SHA512 short hash: 177cc163
Show secret? (y or n)?
y
gpg: AES256 encrypted data
gpg: encrypted with 1 passphrase
Secret: this is a test yo
Done
Backing up…
Format USB flash drive? (y or n)?
y
mkfs.fat 4.1 (2017-01-24)
-----BEGIN PGP MESSAGE-----

jA0ECQMKAWdJZylXXDf/0kUB/rRdX1+5OYVh7iwzM0julwIfDe57slc6LeGeRtDa
KfY4QZkCrseEoZdSZd5mGYQ0ItW9exfBiXN5AU+rbEmzF6VuEWY=
=ul1g
-----END PGP MESSAGE-----
SHA512 hash: 524d8219b17aad59d7cec70f901dfdd449d15f21479740b0111b621cc870e6d82f2f4a0ea8303fb478b24500195325be9c3256d4d5b19700a1cdd1329fc2c71f
SHA512 short hash: 524d8219
Show SHA512 hash as QR code? (y or n)?
n
Done

Done

👍

The following image is now available on USB flash drive.

Secure erase flash drive

$ secure-erase.sh --help
Usage: secure-erase.sh [options]

Options:
  --rounds <rounds>  overwrite n times (defauls to 3)
  --zero             overwrite with zeros obfuscating secure erase
  -h, --help         display help for command

$ secure-erase.sh
Secure erase USB flash drive? (y or n)?
y
Erasing… (iteration 1 of 3)
dd: error writing '/dev/sda1': No space left on device
1868+0 records in
1867+0 records out
1957691392 bytes (2.0 GB, 1.8 GiB) copied, 181.888 s, 10.8 MB/s
Erasing… (iteration 2 of 3)
dd: error writing '/dev/sda1': No space left on device
1868+0 records in
1867+0 records out
1957691392 bytes (2.0 GB, 1.8 GiB) copied, 195.606 s, 10.0 MB/s
Erasing… (iteration 3 of 3)
dd: error writing '/dev/sda1': No space left on device
1868+0 records in
1867+0 records out
1957691392 bytes (2.0 GB, 1.8 GiB) copied, 195.558 s, 10.0 MB/s
Done

Done

👍