seal-hotpkey

#!/bin/bash
# Retrieve the sealed TOTP secret and initialize a USB Security Dongle with it

. /etc/functions

HOTP_SECRET="/tmp/secret/hotp.key"
HOTP_COUNTER="/boot/kexec_hotp_counter"
HOTP_KEY="/boot/kexec_hotp_key"

mount_boot()
{
  TRACE_FUNC
  # Mount local disk if it is not already mounted
  if ! grep -q /boot /proc/mounts; then
    if ! mount -o ro /boot; then
      whiptail $BG_COLOR_ERROR --title 'ERROR' \
        --msgbox "Couldn't mount /boot.\n\nCheck the /boot device in configuration settings, or perform an OEM reset." 0 80
      return 1
    fi
  fi
}

TRACE_FUNC

fatal_error()
{
  echo -e "\nERROR: ${1}; press Enter to continue."
  read
  die "$1"
}

# Use stored HOTP key branding (this might be useful after OEM reset)
if [ -r /boot/kexec_hotp_key ]; then
	HOTPKEY_BRANDING="$(cat /boot/kexec_hotp_key)"
else
	HOTPKEY_BRANDING="HOTP USB Security Dongle"
fi

if [ "$CONFIG_TPM" = "y" ]; then
	DEBUG "Sealing HOTP secret reuses TOTP sealed secret..."
	tpmr unseal 4d47 0,1,2,3,4,7 312 "$HOTP_SECRET" \
		|| fatal_error "Unable to unseal HOTP secret"
else
	# without a TPM, generate a secret based on the SHA-256 of the ROM
	secret_from_rom_hash > "$HOTP_SECRET" || die "Reading ROM failed"
fi

# Store counter in file instead of TPM for now, as it conflicts with Heads
# config TPM counter as TPM 1.2 can only increment one counter between reboots
# get current value of HOTP counter in TPM, create if absent
mount_boot || exit 1

#check_tpm_counter $HOTP_COUNTER hotp \
#|| die "Unable to find/create TPM counter"
#counter="$TPM_COUNTER"
#
#counter_value=$(read_tpm_counter $counter | cut -f2 -d ' ' | awk 'gsub("^000e","")')
#if [ "$counter_value" == "" ]; then
#  die "Unable to read HOTP counter"
#fi

#counter_value=$(printf "%d" 0x${counter_value})

counter_value=1

enable_usb
# While making sure the key is inserted, capture the status so we can check how
# many PIN attempts remain
if ! hotp_token_info="$(hotp_verification info)" ; then
  echo -e "\nInsert your $HOTPKEY_BRANDING and press Enter to configure it"
  read
  if ! hotp_token_info="$(hotp_verification info)" ; then
    # don't leak key on failure
    shred -n 10 -z -u "$HOTP_SECRET" 2> /dev/null
    fatal_error "Unable to find $HOTPKEY_BRANDING"
  fi
fi

# Set HOTP USB Security Dongle branding based on VID
if lsusb | grep -q "20a0:" ; then
	HOTPKEY_BRANDING="Nitrokey"
elif lsusb | grep -q "316d:" ; then
	HOTPKEY_BRANDING="Librem Key"
else
	HOTPKEY_BRANDING="HOTP USB Security Dongle"
fi

# Truncate the secret if it is longer than the maximum HOTP secret
truncate_max_bytes 20 "$HOTP_SECRET"

# Check when the signing key was created to consider trying the default PIN
# (Note: we must avoid using gpg --card-status here as the Nitrokey firmware
# locks up, https://github.com/Nitrokey/nitrokey-pro-firmware/issues/54)
gpg_key_create_time="$(gpg --list-keys --with-colons | grep -m 1 '^pub:' | cut -d: -f6)"
gpg_key_create_time="${gpg_key_create_time:-0}"
DEBUG "Signature key was created at $(date -d "@$gpg_key_create_time")"
now_date="$(date '+%s')"

# Get the number of admin PIN retry attempts remaining
awk_admin_counter_regex='/^\s*Card counters: Admin (\d),.*$/'
awk_get_admin_counter="$awk_admin_counter_regex"' { print gensub('"$awk_admin_counter_regex"', "\\1", "") }'
admin_pin_retries="$(echo "$hotp_token_info" | awk "$awk_get_admin_counter")"
admin_pin_retries="${admin_pin_retries:-0}"
DEBUG "Admin PIN retry counter is $admin_pin_retries"

# Try using factory default admin PIN for 1 month following OEM reset to ease
# initial setup.  But don't do it forever to encourage changing the PIN and
# so PIN attempts are not consumed by the default attempt.
admin_pin="12345678"
month_secs="$((30*24*60*60))"
admin_pin_status=1
if [ "$((now_date - gpg_key_create_time))" -gt "$month_secs" ]; then
	# Remind what the default PIN was in case it still hasn't been changed
	echo "Not trying default PIN ($admin_pin)"
# Never consume an attempt if there are less than 3 attempts left, otherwise
# attempting the default PIN could cause an unexpected lockout before getting a
# chance to enter the correct PIN
elif [ "$admin_pin_retries" -lt 3 ]; then
	echo "Not trying default PIN ($admin_pin), only $admin_pin_retries attempt(s) left"
else
	hotp_initialize "$admin_pin" $HOTP_SECRET $counter_value "$HOTPKEY_BRANDING" >/dev/null 2>&1
	admin_pin_status="$?"
fi

if [ "$admin_pin_status" -ne 0 ]; then
  # prompt user for PIN and retry
  echo ""
  read -s -p "Enter your $HOTPKEY_BRANDING Admin PIN: " admin_pin
  echo -e "\n"
  
  hotp_initialize "$admin_pin" $HOTP_SECRET $counter_value "$HOTPKEY_BRANDING"
  if [ $? -ne 0 ]; then
    echo -e "\n"
    read -s -p "Error setting HOTP secret, re-enter Admin PIN and try again: " admin_pin
    echo -e "\n"
    if ! hotp_initialize "$admin_pin" $HOTP_SECRET $counter_value "$HOTPKEY_BRANDING" ; then
      # don't leak key on failure
      shred -n 10 -z -u "$HOTP_SECRET" 2> /dev/null
      fatal_error "Setting HOTP secret failed"
    fi
  fi
else 
  # remind user to change admin password
  echo -e "\nWARNING: default GPG admin PIN detected: please change this as soon as possible."
fi

# HOTP key no longer needed
shred -n 10 -z -u "$HOTP_SECRET" 2> /dev/null

# Make sure our counter is incremented ahead of the next check
#increment_tpm_counter $counter > /dev/null \
#|| die "Unable to increment tpm counter"
#increment_tpm_counter $counter > /dev/null \
#|| die "Unable to increment tpm counter"

mount -o remount,rw /boot

counter_value=`expr $counter_value + 1`
echo $counter_value > $HOTP_COUNTER \
|| fatal_error "Unable to create hotp counter file"

# Store/overwrite HOTP USB Security Dongle branding found out beforehand
echo $HOTPKEY_BRANDING > $HOTP_KEY \
|| die "Unable to store hotp key file"

#sha256sum /tmp/counter-$counter > $HOTP_COUNTER \
#|| die "Unable to create hotp counter file"
mount -o remount,ro /boot

echo -e "\n$HOTPKEY_BRANDING initialized successfully. Press Enter to continue."
read

exit 0