UNECE R155/R156 Regulatory Requirements

#!/usr/bin/env python3
# UNECE R156 SUMS: software update package verification
import hashlib, hmac, struct

def verify_update_package(package_bytes: bytes, expected_sha256: str,
                           ecdsa_signature: bytes, oem_public_key) -> dict:
    """
    SUMS verification chain per UNECE R156:
    1. Verify SHA-256 hash integrity
    2. Verify ECDSA-P256 signature authenticity
    3. Check update version monotonicity (anti-rollback)
    """
    # Step 1: Integrity check
    actual_hash = hashlib.sha256(package_bytes).hexdigest()
    integrity_ok = actual_hash == expected_sha256

    # Step 2: Authenticity check (ECDSA-P256 signature over SHA-256 hash)
    # Using cryptography library (python-cryptography)
    try:
        from cryptography.hazmat.primitives import hashes
        from cryptography.hazmat.primitives.asymmetric import ec
        oem_public_key.verify(ecdsa_signature,
                              package_bytes,
                              ec.ECDSA(hashes.SHA256()))
        authenticity_ok = True
    except Exception:
        authenticity_ok = False

    # Step 3: Extract and check version from package header
    # Package header: magic(4) + version(4) + ...
    magic = struct.unpack(">I", package_bytes[:4])[0]
    new_version = struct.unpack(">I", package_bytes[4:8])[0]
    current_version = get_ecu_current_version()  # from ECU NVM
    rollback_ok = new_version >= current_version

    return {
        "integrity":    integrity_ok,
        "authenticity": authenticity_ok,
        "anti_rollback": rollback_ok,
        "install": integrity_ok and authenticity_ok and rollback_ok,
    }

def get_ecu_current_version(): return 0x0302  # placeholder