heads/initrd/bin/seal-totp

#!/bin/bash
# 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
TPM_PASSWORD="$2"

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)"
pcrf="/tmp/secret/pcrf.bin"
DEBUG "Sealing TOTP with actual state of PCR0-3"
tpmr pcrread 0 "$pcrf"
tpmr pcrread -a 1 "$pcrf"
tpmr pcrread -a 2 "$pcrf"
tpmr pcrread -a 3 "$pcrf"
DEBUG "Sealing TOTP with boot state of PCR4 (Going to recovery shell extends PCR4)"
# pcr 4 is expected to either:
#  zero on bare coreboot+linuxboot on x86 (boot mode: init)
#  already extended on ppc64 per BOOTKERNEL (skiboot) which boots heads.
# Read from event log to catch both cases, even when called from recovery shell.
tpmr calcfuturepcr 4 >>"$pcrf"
# pcr 5 (kernel modules loaded) is not measured at sealing/unsealing of totp
DEBUG "Sealing TOTP neglecting PCR5 involvement (Dynamically loaded kernel modules are not firmware integrity attestation related)"
# pcr 6 (drive LUKS header) is not measured at sealing/unsealing of totp
DEBUG "Sealing TOTP without PCR6 involvement (LUKS header consistency is not firmware integrity attestation related)"
# pcr 7 is containing measurements of user injected stuff in cbfs
tpmr pcrread -a 7 "$pcrf"
#Make sure we clear the TPM Owner Password from memory in case it failed to be used to seal TOTP
tpmr seal "$TOTP_SECRET" "$TPM_NVRAM_SPACE" 0,1,2,3,4,7 "$pcrf" 312 "" "$TPM_PASSWORD" ||
	{
		shred -n 10 -z -u /tmp/secret/tpm_owner_password 2>/dev/null
		:
		die "Unable to write sealed secret to NVRAM"
	}
#Make sure we clear TPM TOTP sealed if we succeed to seal TOTP
shred -n 10 -z -u "$TOTP_SEALED" 2>/dev/null

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

qrenc "$url"
echo "$url"