heads/initrd/bin/unseal-hotp

#!/bin/bash
# Retrieve the sealed file and counter from the NVRAM, unseal it and compute the hotp

. /etc/functions

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

mount_boot_or_die() {
  TRACE_FUNC
  # Mount local disk if it is not already mounted
  if ! grep -q /boot /proc/mounts; then
    mount -o ro /boot ||
      die "Unable to mount /boot"
  fi
}

TRACE_FUNC

# 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_or_die

#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","")')
#

counter_value=$(cat $HOTP_COUNTER)

if [ "$counter_value" == "" ]; then
  die "Unable to read HOTP counter"
fi

#counter_value=$(printf "%d" 0x${counter_value})
if [ "$CONFIG_TPM" = "y" ]; then
  DEBUG "Unsealing HOTP secret reuses TOTP sealed secret..."
  tpmr unseal 4d47 0,1,2,3,4,7 312 "$HOTP_SECRET" || die "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

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

if ! hotp $counter_value <"$HOTP_SECRET"; then
  shred -n 10 -z -u "$HOTP_SECRET" 2>/dev/null
  die 'Unable to compute HOTP hash?'
fi

shred -n 10 -z -u "$HOTP_SECRET" 2>/dev/null

#Incrementing counter under $HOTP_COUNTER
#
# If for whatever reason, this counter is 5 counts different then on HOTP USB Security dongle, HOTP unseal fails.
#Note: HOTP_COUNTER="/boot/kexec_hotp_counter" is not detached signed under kexec.sig since it changes
#
# TODO: figure out a better alternative then a counter that can be modified on disk
#   As of now, this counter isincreased only in the validated presence of the HOTP dongle being connected per callers
mount -o remount,rw /boot
DEBUG "Incrementing HOTP counter under $HOTP_COUNTER"
counter_value=$(expr $counter_value + 1)
echo $counter_value >$HOTP_COUNTER ||
  die "Unable to create hotp counter file"
mount -o remount,ro /boot

exit 0