scorehsm

Hardware-backed cryptographic module for Linux-based SDV platforms.

STM32L552ZE-Q Nucleo as HSM peripheral over USB to Raspberry Pi. Full V-model — requirements, architecture, implementation, verification. Rust throughout.

Built as a reference implementation for Eclipse SCORE's Security & Cryptography feature (experimental_security_crypto), which has 43 defined requirements and no implementation.

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Architecture

Raspberry Pi (HPC proxy)                STM32L552ZE-Q Nucleo (HSM)
┌─────────────────────────┐             ┌────────────────────────────┐
│  host/ Rust library     │             │  firmware/ Embassy Rust    │
│  ┌─────────────────┐   │             │  ┌──────────────────────┐  │
│  │ Hardware backend│◄──┼── USB CDC ──┼─►│  NS: USB gateway     │  │
│  ├─────────────────┤   │             │  ├──────────────────────┤  │
│  │ SW fallback     │   │             │  │  S:  AES/PKA/HASH    │  │
│  │ (rustcrypto)    │   │             │  │      RNG / Key store │  │
│  └─────────────────┘   │             │  └──────────────────────┘  │
│  Common API             │             │  TrustZone boundary        │
└─────────────────────────┘             └────────────────────────────┘

Key principle: key material never leaves the L55. Only opaque handles cross the USB boundary.

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Hardware

Component	Role
STM32L552ZE-Q NUCLEO-L552ZE-Q	HSM — Cortex-M33 TrustZone, HW AES/PKA/HASH/RNG
Raspberry Pi (USB host)	HPC proxy — runs host library
USB-A to Micro-USB	Power + data — single cable

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Structure

firmware/   — STM32L552 Embassy Rust firmware (HSM device)
host/       — Raspberry Pi Rust library (hardware + software backends)
docs/       — V-model artifacts (requirements, architecture, plans, safety)

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Test Suite

Category	Count	Coverage
Unit tests (host)	54	Safety, transport, crypto, mock backend
Integration tests (ITP)	58	TSR-TIG, NMG, SMG, RLG, SSG, IVG, CG
Qualification tests (QTE)	57	All 16 FSRs (FSR-01 through FSR-16)
Feature tests	104	SW backend, session, update, activation, onboard comm, certs, constant-time
Doc-tests	1	API examples
Total	274

# Run all tests
cargo test --workspace --features "mock,certs"

# Clippy
cargo clippy --workspace --all-targets --features "mock,certs" -- -D warnings

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Status

Phases 0–9 complete. Phase 10 evidence collection complete — 274 tests passing, CI green, docs updated. HIL hardware verification (4 tests on Pi + Nucleo) pending.

License

Apache-2.0 — see LICENSE.