P256-CM4

A (mostly) rust re-implementation of [Emill/P256-Cortex-M4].

Rust 1.59.0 stabilized the [global_asm] macro which allows for this to be compiled without any additional tooling. No build.rs script or external assembler required.

Limitations

This is not yet complete, it lacks interoperability with other targets (via RustCrypto traits or compile-time switches). See [ycrypto/p256-cortex-m4] for an interoperable solution.

This lacks the configurability of the original source because rust features are less powerful than C pre-processor macros. Use [ycrypto/p256-cortex-m4-sys] if you require configurability.

Comparisons

As measured on a STM32WLE5.

| Implementation | Signing Cycles (appx) | Verify Cycles (appx) | Flash Size (appx) | |----------------|-----------------------|----------------------|-------------------| | Hardware PKA | 5,211,859 | 10,516,860 | 1,582 B | | [RustCrypto] | 7,856,436 | 14,303,277 | 49 kiB | | p256-cm4 | 442,754 | 1,225,746 | 10 kiB |

Maintainers Notes

Testing

Install [probe-run].

Adjust .cargo/config.toml, memory.x, testsuite/Cargo.toml, and the clock setup for your target.

bash DEFMT_LOG=trace cargo test -p testsuite

ASM Generation

Send the GCC ASM from [Emill/P256-Cortex-M4] through the pre-processor.

bash arm-none-eabi-gcc -O0 -ffunction-sections -fdata-sections -g -fno-omit-frame-pointer -mthumb -march=armv7e-m -Wall -Wextra -std=c11 -march=armv7e-m -c P256-Cortex-M4/p256-cortex-m4-asm-gcc.S -E > asm.s