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d937426306
On machines without a TPM, we'd still like some way for the BIOS to attest that it has not been modified. With a Librem Key, we can have the BIOS use its own ROM measurement converted to a SHA256sum and truncated so it fits within an HOTP secret. Like with a TPM, a malicious BIOS with access to the correct measurements can send pre-known good measurements to the Librem Key. This approach provides one big drawback in that we have to truncate the SHA256sum to 20 characters so that it fits within the limitations of HOTP secrets. This means the possibility of collisions is much higher but again, an attacker could also capture and spoof an existing ROM's measurements if they have prior access to it, either with this approach or with a TPM. Signed-off-by: Kyle Rankin <kyle.rankin@puri.sm>
119 lines
3.4 KiB
Bash
Executable File
119 lines
3.4 KiB
Bash
Executable File
#!/bin/bash
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# Retrieve the sealed TOTP secret and initialize a USB Security dongle with it
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. /etc/functions
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HOTP_SECRET="/tmp/secret/hotp.key"
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HOTP_COUNTER="/boot/kexec_hotp_counter"
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HOTP_KEY="/boot/kexec_hotp_key"
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mount_boot()
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{
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TRACE "Under /bin/seal-htopkey:mount_boot"
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# Mount local disk if it is not already mounted
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if ! grep -q /boot /proc/mounts ; then
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mount -o ro /boot \
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|| recovery "Unable to mount /boot"
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fi
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}
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TRACE "Under /bin/seal-hotpkey"
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# Use stored HOTP key branding (this might be useful after OEM reset)
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if [ -r /boot/kexec_hotp_key ]; then
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HOTPKEY_BRANDING="$(cat /boot/kexec_hotp_key)"
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else
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HOTPKEY_BRANDING="HOTP USB Security Dongle"
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fi
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if [ "$CONFIG_TPM" = "y" ]; then
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DEBUG "Sealing HOTP secret reuses TOTP sealed secret..."
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tpmr unseal 4d47 0,1,2,3,4,7 312 "$HOTP_SECRET" \
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|| die "Unable to unseal HOTP secret"
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else
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# without a TPM, use the first 20 characters of the ROM SHA256sum
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secret_from_rom_hash > "$HOTP_SECRET"
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fi
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# Store counter in file instead of TPM for now, as it conflicts with Heads
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# config TPM counter as TPM 1.2 can only increment one counter between reboots
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# get current value of HOTP counter in TPM, create if absent
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mount_boot
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#check_tpm_counter $HOTP_COUNTER hotp \
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#|| die "Unable to find/create TPM counter"
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#counter="$TPM_COUNTER"
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#
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#counter_value=$(read_tpm_counter $counter | cut -f2 -d ' ' | awk 'gsub("^000e","")')
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#if [ "$counter_value" == "" ]; then
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# die "Unable to read HOTP counter"
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#fi
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#counter_value=$(printf "%d" 0x${counter_value})
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counter_value=1
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enable_usb
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if ! hotp_verification info ; then
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echo "Insert your $HOTPKEY_BRANDING and press Enter to configure it"
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read
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if ! hotp_verification info ; then
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# don't leak key on failure
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shred -n 10 -z -u "$HOTP_SECRET" 2> /dev/null
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die "Unable to find $HOTPKEY_BRANDING"
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fi
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fi
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# Set HOTP USB Security Dongle branding based on VID
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if lsusb | grep -q "20a0:" ; then
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HOTPKEY_BRANDING="Nitrokey"
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elif lsusb | grep -q "316d:" ; then
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HOTPKEY_BRANDING="Librem Key"
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else
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HOTPKEY_BRANDING="HOTP USB Security Dongle"
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fi
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echo -e ""
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read -s -p "Enter your $HOTPKEY_BRANDING Admin PIN: " admin_pin
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echo -e "\n"
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hotp_initialize "$admin_pin" $HOTP_SECRET $counter_value "$HOTPKEY_BRANDING"
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if [ $? -ne 0 ]; then
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echo -e "\n"
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read -s -p "Error setting HOTP secret, re-enter Admin PIN and try again: " admin_pin
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echo -e "\n"
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if ! hotp_initialize "$admin_pin" $HOTP_SECRET $counter_value "$HOTPKEY_BRANDING" ; then
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# don't leak key on failure
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shred -n 10 -z -u "$HOTP_SECRET" 2> /dev/null
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die "Setting HOTP secret failed"
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fi
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fi
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# HOTP key no longer needed
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shred -n 10 -z -u "$HOTP_SECRET" 2> /dev/null
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# Make sure our counter is incremented ahead of the next check
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#increment_tpm_counter $counter > /dev/null \
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#|| die "Unable to increment tpm counter"
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#increment_tpm_counter $counter > /dev/null \
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#|| die "Unable to increment tpm counter"
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mount -o remount,rw /boot
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counter_value=`expr $counter_value + 1`
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echo $counter_value > $HOTP_COUNTER \
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|| die "Unable to create hotp counter file"
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# Store/overwrite HOTP USB Security Dongle branding found out beforehand
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echo $HOTPKEY_BRANDING > $HOTP_KEY \
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|| die "Unable to store hotp key file"
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#sha256sum /tmp/counter-$counter > $HOTP_COUNTER \
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#|| die "Unable to create hotp counter file"
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mount -o remount,ro /boot
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echo -e "\n$HOTPKEY_BRANDING initialized successfully. Press Enter to continue."
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read
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exit 0
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