install.fairie/home/.chezmoiscripts/universal/run_before_03-decrypt-age-key.sh.tmpl

#!/usr/bin/env bash
# @file Chezmoi-Age Secret Decryption
# @brief Ensures `age` is installed and then decrypts the `home/key.txt.age` file so that Chezmoi can utilize encrypted files
# @description
#     This script begins by ensuring `age` is installed, the defualt program Chezmoi utilizes for handling encryption.
#     The script then allows you to generate the decrypted `~/.config/age/chezmoi.txt` file by prompting you for the password
#     to `home/key.txt.age` which is the encrypted encryption key file for using Chezmoi to add encrypted files to your Install
#     Doctor fork. If no password is passed to the decryption password prompt, then all of the `encrypted_` files in the fork
#     are deleted so that Chezmoi does not try to decrypt files without a decryption key file.
#
#     ## Headless Installs
#
#     If you do not want the script to prompt you for a password, then you can pass in an environment variable with
#     `HEADLESS_INSTALL=true`. This variable ensures that nothing requiring input from the user blocks the provisioning process.
#     If you want to automate a headless install that requires access to `encrypted_` files and encrypted variables, then
#     you can save the decrypted Age key to `~/.config/age/chezmoi.txt` prior to running `bash <(curl -sSL https://install.doctor/start)`.
#
#     Alternatively, you can pass in your Age decryption passphrase in using the `AGE_PASSWORD` environment variable.
#     Install Doctor will use this variable along with expect to headlessly automate the password prompt during the
#     decryption process.
#
#     ## GPG
#
#     It is also possible to configure Chezmoi to utilize GPG instead of Age. This might be beneficial if you want to
#     use a smart card / YubiKey for hardware-backed encryption. Otherwise, Age is a great encryption tool.
#
#     ## Notes
#
#     _It is possible that hardware-based smart-card-like GPG encryption might not work properly with Chezmoi yet.
#     Learned this by attempting to use a YubiKey GPG setup using [this guide](https://github.com/drduh/YubiKey-Guide) and trying to get it to work with Chezmoi._

{{ includeTemplate "universal/logg-before" }}
{{ includeTemplate "universal/profile-before" }}

# @description Helper function utilized by [[decryptKey]] that removes all `encrypted_` files from the Chezmoi source
#     if the Age decryption process fails due to wrong password or from not being set up yet.
decryptionFailure() {
  logg info 'Proceeding without decrypting age encryption key stored at ~/.local/share/chezmoi/home/key.txt.age'
  logg info 'To have Chezmoi handle your encryption (so you can store your private files publicly) take a look at https://shorturl.at/jkpzG'
  logg info 'Removing all files that begin with encrypted_ because decryption failed'
  find "${XDG_DATA_HOME:-$HOME/.local/share}/chezmoi" -type f -name "encrypted_*" | while read ENCRYPTED_FILE; do
    logg info "Removing $ENCRYPTED_FILE"
    rm -f "$ENCRYPTED_FILE"
  done
}

# @description Helper function utilized by [[decryptKey]] to ensure the `age` command is available
installAge() {
  if ! command -v age > /dev/null; then
    logg info 'Running brew install age'
    brew install --quiet age
  fi
}

# @description Helper function utilized by [[decryptKey]] to ensure the `expect` command is available
installExpect() {
  if ! command -v expect > /dev/null; then
    logg info 'Running brew install expect'
    brew install --quiet expect
  fi
}

# @description Decrypt private Chezmoi key if it is not already present at `${XDG_CONFIG_HOME:-$HOME/.config}/age/chezmoi.txt`
decryptKey() {
  if command -v age > /dev/null; then
    if [ ! -f "${XDG_CONFIG_HOME:-$HOME/.config}/age/chezmoi.txt" ]; then
      mkdir -p "${XDG_CONFIG_HOME:-$HOME/.config}/age"
      if [ -z "$AGE_PASSWORD" ]; then
        logg star 'PRESS ENTER if you have not set up your encryption token yet'
        age --decrypt --output "${XDG_CONFIG_HOME:-$HOME/.config}/age/chezmoi.txt" "{{ .chezmoi.sourceDir }}/key.txt.age" || EXIT_CODE=$?
        if [ -n "$EXIT_CODE" ]; then
          decryptionFailure
        else
          logg success 'The encryption key was successfully decrypted'
        fi
      else
        installExpect
        expect -c "set timeout -1
        spawn age --decrypt --output "${XDG_CONFIG_HOME:-$HOME/.config}/age/chezmoi.txt" "${XDG_DATA_HOME:-$HOME/.local/share}/chezmoi/home/key.txt.age"
        expect \"Enter passphrase:\"
        send \"${AGE_PASSWORD}\r\"
        expect eof" &> /dev/null || EXIT_CODE=$?
        if [ -n "$EXIT_CODE" ]; then
          logg info 'There was an issue decrypting the key.txt.age file with the provided AGE_PASSWORD'
          decryptionFailure
        else
          logg info 'The encryption key was successfully decrypted using expect and the provided AGE_PASSWORD'
        fi
      fi
    fi
  fi
}

### Only run decryption process if HEADLESS_INSTALL variable is not set
if [ -z "$HEADLESS_INSTALL" ]; then
  installAge
  decryptKey
elif [ -n "$HEADLESS_INSTALL" ] && [ -n "$AGE_PASSWORD" ]; then
  installAge
  decryptKey
else
  logg info 'Skipping Age key decryption process - HEADLESS_INSTALL and AGE_PASSWORD should be passed in as env variables to automate the process'
fi

### Ensure proper permissions on private key
if [ -f "${XDG_CONFIG_HOME:-$HOME/.config}/age/chezmoi.txt" ]; then
  logg info 'Ensuring proper permissions on Chezmoi / age decryption key'
  logg info 'Chezmoi / age decryption key is stored in '"${XDG_CONFIG_HOME:-$HOME/.config}/age/chezmoi.txt"
  chmod 600 "${XDG_CONFIG_HOME:-$HOME/.config}/age/chezmoi.txt"
fi