Streaming SPHINCS+ for Embedded Devices at the Example of TPMs

This is the implementation work for the paper Streaming SPHINCS+ for Embedded Devices using the Example of TPMs which can be found at https://eprint.iacr.org/2021/1072. We present an implementation of the hash-based post-quantum signature scheme SPHINCS+ that enables heavily memory-restricted devices to sign messages by streaming-out a signature during its computation and to verify messages by streaming-in a signature. We demonstrate our implementation in the context of Trusted Platform Modules (TPMs) by proposing a SPHINCS+ integration and a streaming extension for the TPM specification.

This repository has the following structure:

• sphincsplus/ contains the SPHINCS+ reference code with our changes to enable streaming. It can be built stand-alone, i.e., without the TPM firmware. More information is found in the respective README.md of that folder.
• tpmfirmware/ contains the TPM code that is taken from the Official TPM 2.0 Reference Implementation (by Microsoft). It includes WolfSSL as a git submodule.
• src/ contains our code that integrates the streaming SPHINCS+ code into the TPM.

Clone with --recursive for external dependencies (wolfSSL).

Raspberry Pi Software Setup

We tested this with the May 7th 2021 (5.10) Release of Raspberry Pi OS Lite: Our micro-sd card is available under /dev/sdc but that might differ from system to system change /dev/sdX accordingly.

wget https://downloads.raspberrypi.org/raspios_lite_armhf/images/raspios_lite_armhf-2021-05-28/2021-05-07-raspios-buster-armhf-lite.zip
unzip 2021-05-07-raspios-buster-armhf-lite.zip   
# writes to 2021-05-07-raspios-buster-armhf-lite.img
# use dd to write to sdcard
sudo dd if=2021-05-07-raspios-buster-armhf-lite.img of=/dev/sdc bs=4K status=progress

Either configure the Raspberry Pi to run an ssh server, control it via UART, or connect a monitor and keyboard to it. Headless Raspberry Pi How To might help in this regard.

Enable SPI after the first boot

The SPI interface has to be enabled in order to reproduce our results. This can be achieved using the raspi-config tool shipped with raspbian.

#Interfaces -> SPI 
sudo raspi-config

Install missing software

We were able to build using the following dependencies:

sudo apt install git build-essential autoconf autoconf-archive libssl-dev

Wiring of Raspberry Pi 4 and STM32F4 Discovery

The SPI controller of the raspberry pi need to be enabled and the STM32F4 UART needs to be connected to a serial connector either on the raspberry pi or a usb device. Wire the raspberry pi and the stm32f4 in the following manner.

Raspberry PI4

        3v3 oo 5V             
            oo             
            oo             
            oo             
            oo             
            oo             
            oo             
            oo             
            oo             
      MOSI  oo             
      MISO  oo             
      SCLK  oo CE1            
      GND   oo            
            oo             
            oo             
            oo             
            oo             
            oo             
            oo 
      GND   oo 

STM32F4 DISCO

         GND   oo  GND
               oo             
               oo             
               oo             
               oo             
               oo             
UART RX (PA3)  oo  UART TX (PA2)
  SCLK  (PA5)  oo  CE1  (PA4)           
  MOSI  (PA7)  oo  MISO (PA6)             

Reproducing the Measurements

On the device programming the stm32f4

This requires openocd, arm-none-eabi-gcc, and make. install them on ubuntu using:

apt install make gcc-arm-none-eabi openocd 

start openocd

#in src/hal
openocd -f stm32f4.cfg

program the stm32f4

#in src/ 
make TARGET=stm32f4 -j$(nproc)
gdb -ex "set pagination off" -ex "tar extended-remote :3333" -ex "load" -ex "run" build/tpm.elf

On the Raspberry PI

Within this repository cloned on the raspberry pi execute:

cd tpmfirmware/TPMCmd/
./bootstrap
./configure
make -j$(nproc)
test/command_test -S1

The Options for the S-switch are:

            0 - sphincs_sha256_128f_robust
            1 - sphincs_sha256_128s_robust
            2 - sphincs_sha256_192f_robust
            3 - sphincs_sha256_192s_robust
            4 - sphincs_sha256_256f_robust
            5 - sphincs_sha256_256s_robust
            6 - sphincs_sha256_128f_simple
            7 - sphincs_sha256_128s_simple
            8 - sphincs_sha256_192f_simple
            9 - sphincs_sha256_192s_simple
           10 - sphincs_sha256_256f_simple
           11 - sphincs_sha256_256s_simple
           12 - sphincs_shake256_128f_robust
           13 - sphincs_shake256_128s_robust
           14 - sphincs_shake256_192f_robust
           15 - sphincs_shake256_192s_robust
           16 - sphincs_shake256_256f_robust
           17 - sphincs_shake256_256s_robust
           18 - sphincs_shake256_128f_simple
           19 - sphincs_shake256_128s_simple
           20 - sphincs_shake256_192f_simple
           21 - sphincs_shake256_192s_simple
           22 - sphincs_shake256_256f_simple
           23 - sphincs_shake256_256s_simple