Files
MicrOBU/microbu-esp32c5/pki/uml-l0-rca/reference-generator/PROVENANCE.txt
T
Ashin Walpola 0e9525162d Keep the colleague's microbu-esp32c5 tree in this repository
obu-firmware builds against vanetza-idf from microbu-esp32c5/external, but
that tree was gitignored, so a clone of this repository could not build the
firmware it ships. It is now committed here as ordinary files in its own
folder, microbu-esp32c5/: the colleague's commit cf4b99f plus the V2X2MAP
bridge's signature verification (--trust) used on the bench. Nothing is
fetched from or pushed to the colleague's repository; this repository and
its remotes carry everything. The folder's own .gitignore keeps build output,
downloaded components and private key material out, as it did there; the
committed file set is identical to that repository's tracked files.

The ESP32-C5 is still flashed from obu-firmware/, which only takes
vanetza-idf from microbu-esp32c5/, so the two stay separate folders.
FLASHING.md says how to take a newer version of the colleague's tree (copy
it over the folder, rebuild, test, commit).
2026-09-23 17:46:40 +02:00

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Reference notes
===============
Pinned upstream commit:
e3bb3b82480d6df4237e2a8c35ea0dd7eade25b4
The upstream commit's root generator:
1. constructs a ToBeSignedCertificate;
2. serializes it using rasn::oer::encode();
3. calls PrivateKey::sign(hash_alg, &tbs_bytes, None);
4. inserts the returned IEEE 1609.2 Signature into an ExplicitCertificate.
The pinned c-its PrivateKey::sign() implementation for SHA-256 computes:
SHA256(
SHA256(tbs_bytes)
||
SHA256(signer_info)
)
For a self-signed root, signer_info is the empty byte string because the root
generator passes None.
This bundle uses that exact upstream code for the cryptographic operation.
`rebuild_registered_rca.py` keeps the registered TBS/public key unchanged and uses
the registered encrypted key. `create_new_root.py` creates a new encrypted key and
replaces the template public key for a separate, unregistered candidate root. In
both cases the scalar reaches Rust only through standard input.