Suitability of STM32L432KC?

[NIIBE Yutaka]

Hello,

In the development history of mine, I tried:

	STM32L432
        GD32VF103

But I don't use them for Gnuk.  Let me explain.


Terminada <gnupg.org at terminada.io> wrote:
> I am wondering about the suitability of STM32L432KC chip if I was to 
> build a FST-01SZ equivalent.

Chopstx has support of STM32L432 for its core, USART driver and USB
driver.  I use STM32L432 for my card reader implementation (named TTXS),
using Chopstx.

In this situation, if we will implement RNG driver for STM32L432 or port
the ADC driver (for NeuG), it is possible to *run* Gnuk on the MCU.

I didn't do that, however, because I'm not confident enough if it can
run securely.

The code of Gnuk assumes the MCU is *not* that good, that is,

	- without (better) branch predictor
	- without cache (or flash accelerator)

In other words, our unique/peculiar approach is: assuming use of
not-that-good MCU, we can keep the code simpler.

Please note that, in the code of Gnuk:

	- The execution path may depend on secret values.
	- It may have table access which depends on secret values.

This is "feature", not bug.

> "Core: Arm® 32-bit Cortex®-M4 CPU with FPU,Adaptive real-time 
> accelerator (ART Accelerator™) allowing 0-wait-state execution
> from Flash memory, frequency up to 80 MHz, MPU, 100DMIPS and DSP 
> instructions"

My concern is possible side-channel attacks against this accelerator.


IIUC, GD32F103 (on FST-01SZ) has SRAM and SPI Flash ROM, and the
contents of Flash are copied into SRAM at boot.  Table access with
secret values is considered secure on the MCU (against possible
side-channel attacks).
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