heads/initrd/bin/seal-totp

#!/bin/sh
# Generate a random secret, seal it with the PCRs
# and write it to the TPM NVRAM.
#
# Pass in a hostname if you want to change it from the default string
#

. /etc/functions

TRACE "Under /bin/seal-totp"

TPM_NVRAM_SPACE=4d47

HOST="$1"
if [ -z "$HOST" ]; then
	HOST="TPMTOTP"
fi

TOTP_SECRET="/tmp/secret/totp.key"
TOTP_SEALED="/tmp/secret/totp.sealed"

dd \
	if=/dev/urandom \
	of="$TOTP_SECRET" \
	count=1 \
	bs=20 \
	2>/dev/null \
|| die "Unable to generate 20 random bytes"

secret="`base32 < $TOTP_SECRET`"

# Use the current values of the PCRs, which will be read
# from the TPM as part of the sealing ("X").
# PCR4 == 0 means that we are still in the boot process and
# not a recovery shell.
# should this read the storage root key?
if ! tpm sealfile2 \
	-if "$TOTP_SECRET" \
	-of "$TOTP_SEALED" \
	-hk 40000000 \
	-ix 0 X \
	-ix 1 X \
	-ix 2 X \
	-ix 3 X \
	-ix 4 0000000000000000000000000000000000000000 \
	-ix 7 X \
; then
	shred -n 10 -z -u "$TOTP_SECRET" 2> /dev/null
	die "Unable to seal secret"
fi

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


# to create an nvram space we need the TPM owner password
# and the TPM physical presence must be asserted.
#
# The permissions are 0 since there is nothing special
# about the sealed file
tpm physicalpresence -s \
|| warn "Warning: Unable to assert physical presence"

# Try to write it without the password first, and then create
# the NVRAM space using the owner password if it fails for some reason.
if ! tpm nv_writevalue \
	-in $TPM_NVRAM_SPACE \
	-if "$TOTP_SEALED" \
; then
	warn 'NVRAM space does not exist? Owner password is required'
	read -s -p "TPM Owner password: " tpm_password
	echo

	tpm nv_definespace \
		-in $TPM_NVRAM_SPACE \
		-sz 312 \
		-pwdo "$tpm_password" \
		-per 0 \
	|| die "Unable to define NVRAM space"

	tpm nv_writevalue \
		-in $TPM_NVRAM_SPACE \
		-if "$TOTP_SEALED" \
	|| die "Unable to write sealed secret to NVRAM"
fi

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

url="otpauth://totp/$HOST?secret=$secret"
secret=""

qrenc "$url"
echo "$url"