STM32 firmware for Cryptech Alpha board

The Alpha board is our first full prototype for an open-source hardware security module (HSM). It is a custom board with an STM32 Cortex-M4 microcontroller and an Artix-7 FPGA, flash-based keystore, separate memory for the Key Encryption Key, etc. See the hardware repository for schematics and production files. See the wiki for design documents.

The code in this repository builds the firmware that provides the HSM functionality on the Alpha board.

There is some residual code here to support the "dev-bridge" board, a daughterboard for the Novena, which talks to the Novena's FPGA through the high-speed expansion connector. Only a few of these boards were ever made, and all development/testing ceased as soon as the Alpha became available, so the dev-bridge should be considered deprecated, and support may be removed in the future.

Copyrights

The license for all work done on this in the CrypTech project is a 3-clause BSD license.

Third-party components, as well as code generated using the STMicroelectronics initialization code generator STM32CubeMX, or adapted from STM example/support code, may have different licensing, detailed below.

Components

Libraries

mbed - A stripped down copy of the ARM CMSIS library, copied from the mbed github (see libraries/mbed/README.txt for details). The bulk of this library is covered under 3-clause BSD licenses from either ARM or STMicroelectronics, but one file is covered under an Apache license from ARM.
libhal - Build directory for our own Hardware Adaption Library (hardware-independent Cryptech components). Source is expected to be in sw/libhal.
libtfm - Build directory for "Tom's Fast Math", which is used heavily for bignum math in the RSA and ECDSA code. This code is covered under an unrestricted public domain license, and source is expected to be in sw/thirdparty/libtfm.
libcli - Build directory for a third-party Command Line Interface library. The source is not currently under sw/thirdparty because the license is LGPLv2.1; we are negotiating to see if we can get a BSD-compatible license for it.
libprof - A port of the gmon profiling package, to be used in development only, not in production code (obviously). The licensing is a mix of BSD and "Cygwin license", which now seems to be LGPLv3.

Projects

These directories build different firmware images for the Alpha board.

hsm - Firmware providing HSM functionality. Clients communicate via RPC requests on the USER USB port, or interactively on the MGMT USB port.
bootloader - The first thing that runs on the device. It either starts the primary firmware, or installs new firmware.
board-test - Tests of hardware components.
cli-test - Test of the CLI itself, plus some interactive tests of hardware components. Duplicates way too much of the HSM CLI.
libhal-test - A framework for running the libhal component tests. Hasn't been run in a while, probably still works.

Building

Our primary build environments are Debian and Ubuntu, but this should work on any system with Gnu tools installed.

The following packages need to be installed:

$ apt-get install gcc-arm-none-eabi gdb-arm-none-eabi openocd

The Makefile assumes that all Cryptech repositories have been fetched into a canonical directory structure, e.g. libhal and thirdparty are siblings to this directory, under sw.

To build the source code, issue make from the top level directory (where this file is). The first time, this will build the complete STM CMSIS library. A subsequent make clean will not clean away the CMSIS library, but a make distclean will.

Installing

Do bin/flash-target from the top level directory (where this file is) to flash a built image into the microcontroller. See the section ST-LINK below for information about the actual hardware programming device needed.

Example loading the HSM firmware:

$ make hsm
$ ./bin/flash-target projects/hsm/hsm

At this point, the STM32 will reset into the bootloader which flashes the blue LED five times in one second, and then jumps to the primary firmware.

Once the bootloader is installed, regular firmware can be loaded without an ST-LINK cable like this:

$ cryptech_upload --firmware -i projects/hsm/hsm.bin

Then reboot the Alpha board.

ST-LINK

To program the MCU, an ST-LINK adapter is used. The cheapest way to get one is to buy an evaluation board with an ST-LINK integrated, and pinouts to program external chips. This should work with any evaluation board from STM; we have tested with STM32F4DISCOVERY (with ST-LINK v2.0) and NUCLEO-F411RE (with ST-LINK v2.1).

The ST-LINK programming pins is called J1 and is near the CrypTech logo printed on the circuit board. The pin-outs is shown on the circuit board (follow the thin white line from J1 to the white box with STM32_SWD written in it). From left to right, the pins are

3V3, CLK, GND, I/O, NRST and N/C

This matches the pin-out on the DISCO and NUCLEO boards we have tried.

First remove the pair of ST-LINK jumpers (CN4 on the DISCO, CN2 on the NUCLEO). Then find the 6-pin SWD header on the left of the STM board (CN2 on the DISCO, CN4 on the NUCLEO), and connect them to the Alpha board:

NUCLEO / DISCO           CRYPTECH ALPHA
--------------           --------------
* 1 VDD_TARGET      <->  3V3
* 2 SWCLK / T_JTCK  <->  CLK
* 3 GND             <->  GND
* 4 SWDIO / T_JTMS  <->  IO
* 5 NRST / T_NRST   <->  NRST
* 6 N/C

The Alpha board should be powered on before attempting to flash it.

Debugging the firmware

This site shows several ways to use various debuggers to debug the firmware in an STM32.

There is a shell script called 'bin/debug' that starts an OpenOCD server and GDB. Example:

$ ./bin/debug projects/hsm/hsm

Once in GDB, issue monitor reset halt to reset the STM32 before debugging.

Remember that the first code to run will be the bootloader, but if you do e.g. break main and continue you will end up in main() after the bootloader has jumped there.