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/vanetza/security/decap_service.hpp

@@ -0,0 +1,91 @@
+#ifndef F815BB22_3075_4A9D_9385_07876D800765
+#define F815BB22_3075_4A9D_9385_07876D800765
+
+#include <vanetza/common/its_aid.hpp>
+#include <vanetza/net/packet_variant.hpp>
+#include <vanetza/security/certificate_validity.hpp>
+#include <vanetza/security/hashed_id.hpp>
+#include <vanetza/security/secured_message.hpp>
+#include <vanetza/security/verify_service.hpp>
+#include <boost/optional/optional.hpp>
+#include <boost/variant/variant.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+
+/**
+ * \brief Input data for decapsulating a secured message.
+ * 
+ * The structure is equivalent to VerifyRequest, however, decapsulation may
+ * also deal with decryption in future versions.
+ * 
+ * \see TS 102 723-8 v1.1.1 SN-DECAP.request
+ */
+struct DecapRequest
+{
+    DecapRequest(SecuredMessageView sec_msg_view) : sec_packet(sec_msg_view) {}
+    SecuredMessageView sec_packet;
+};
+
+/**
+ * \brief SN-DECAP.confirm report codes
+ * \see TS 102 723-8 v1.1.1 table 27 (report field)
+ * 
+ * Instead of duplicating VerificationReport values and the linked burden keeping
+ * these values consistent, DecapReport is a variant incorporating VerificationReport.
+ * When decryption is implemented, a DecryptionReport may be added to the variant.
+ * 
+ * The boost::blank entry indicates that the SecuredMessage was neither signed nor encrypted.
+ */
+using DecapReport = boost::variant<boost::blank, VerificationReport>;
+
+/**
+ * \brief Check if report indicates a successful decapsulation.
+ *
+ * Either verification or decryption needs to be successful.
+ * An unsecured message cannot lead to a succesful decapsulation result.
+ * 
+ * \param report to check
+ * \return true if either verification or decryption was successful
+ */
+bool is_successful(const DecapReport& report);
+
+/**
+ * \brief Check if decapsulation report matches a particular verification report.
+ * 
+ * \param decap decapsulation report
+ * \param verification verification report
+ * \return true if decapsulation matches verification
+ */
+bool operator==(const DecapReport& decap, VerificationReport verification);
+bool operator==(VerificationReport verification, const DecapReport& decap);
+
+/**
+ * \brief SN-DECAP.confirm
+ * \see TS 102 723-8 v1.1.1 table 27
+ */
+struct DecapConfirm
+{
+    /**
+     * Build DecapConfirm from verify outcome and secured message.
+     * 
+     * \param verify_confirm outcome of verification
+     * \param msg_view view of secured message
+     * \return decapsulation confirmation
+     */
+    static DecapConfirm from(VerifyConfirm&& verify_confirm, const SecuredMessageView& msg_view);
+    
+    PacketVariant plaintext_payload; // mandatory (plaintext_packet_length also covered by data type)
+    DecapReport report; // mandatory
+    CertificateValidity certificate_validity; // non-standard extension
+    boost::optional<HashedId8> certificate_id; // optional
+    ItsAid its_aid; // mandatory (its_ait_lenth also covered by data type)
+    ByteBuffer permissions; // mandatory
+};
+
+} // namespace security
+} // namespace vanetza
+
+#endif /* F815BB22_3075_4A9D_9385_07876D800765 */