Keep vanetza-idf in obu-firmware, so a plain clone builds the firmware

obu-firmware builds against the vanetza-idf C-ITS library, which until now
came from the colleague's microbu-esp32c5 tree beside the repository and was
not tracked here, so a clone of this repository could not build the firmware
it ships. The library alone is now part of obu-firmware, as
obu-firmware/external/vanetza-idf: their external/vanetza-idf at commit
cf4b99f, unchanged (9775 files; see its PROVENANCE.md). CMake takes it from
there by default; -DVANETZA_IDF_DIR still points the build elsewhere.

The rest of the colleague's tree (their own VAM firmware, PKI tooling,
station-link Python tools, the V2X2MAP bridge) stays out of this repository
and gitignored; nothing is pushed to their repository. NOTES.md, docs/06,
TODO.md and the pcap verifier's usage line point at the new location.

obu-firmware/external/vanetza-idf/tools/pki/at_response.cpp

@@ -0,0 +1,74 @@
+#include "at_response.hpp"
+#include "asn1.hpp"
+#include "exception.hpp"
+#include "hashed_id8.hpp"
+#include "security_module.hpp"
+#include "signed_data.hpp"
+#include "validation.hpp"
+#include <vanetza/asn1/security/EtsiTs102941Data.h>
+#include <vanetza/asn1/security/InnerAtResponse.h>
+#include <vanetza/common/its_aid.hpp>
+
+namespace vanetza
+{
+namespace pki
+{
+
+AuthorizationResponse parse_authorization_response(SecurityModule& security, const ByteBuffer& decrypted,
+    const Certificate& aa_certificate)
+{
+    SignedData outer;
+    if (!outer.decode(decrypted)) {
+        throw DecodingFailure("decoding signed authorization response failed");
+    }
+    if (outer->content->present != Vanetza_Security_Ieee1609Dot2Content_PR_signedData) {
+        throw DecodingFailure("authorization response content is not signedData");
+    }
+    const Vanetza_Security_SignedData_t& sd = *outer->content->choice.signedData;
+
+    // Per TS 102 941 §6.2.3.3.2 the AA signs with signer = digest(AA cert).
+    const HashedId8 aa_hid8 = aa_certificate.calculate_hashed_id8(security);
+    if (sd.signer.present != Vanetza_Security_SignerIdentifier_PR_digest) {
+        throw DecodingFailure("authorization response must have signer = digest");
+    }
+    if (sd.signer.choice.digest != aa_hid8.octets) {
+        throw VerificationFailure("authorization response signer digest does not match AA certificate");
+    }
+
+    if (sd.tbsData->headerInfo.psid != aid::SCR) {
+        throw DecodingFailure("authorization response PSID is not SCR");
+    }
+
+    if (!validate(security, sd, aa_certificate.raw())) {
+        throw VerificationFailure("authorization response signature does not verify against AA certificate");
+    }
+
+    const Vanetza_Security_Opaque_t* inner_opaque = get_signed_payload(outer->content);
+    if (!inner_opaque) {
+        throw DecodingFailure("authorization response carries no unsecured signed payload");
+    }
+
+    AuthorizationResponseData inner = AuthorizationResponseData::from_opaque(*inner_opaque);
+    if (inner->version != Vanetza_Security_Version_v1) {
+        throw DecodingFailure("inner EtsiTs102941Data version is not v1");
+    }
+
+    const Vanetza_Security_InnerAtResponse_t& at_resp = inner->content.choice.authorizationResponse;
+
+    AuthorizationResponse result;
+    result.code = AuthorizationResponseCode { at_resp.responseCode };
+    result.request_hash.assign(at_resp.requestHash.buf, at_resp.requestHash.buf + at_resp.requestHash.size);
+
+    if (at_resp.certificate) {
+        result.certificate = Certificate(*at_resp.certificate);
+    }
+
+    if (at_resp.responseCode == Vanetza_Security_AuthorizationResponseCode_ok && !result.certificate) {
+        throw DecodingFailure("authorization response code is ok but no certificate is included");
+    }
+
+    return result;
+}
+
+} // namespace pki
+} // namespace vanetza