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/v2/recipient_info.hpp

@@ -0,0 +1,76 @@
+#ifndef RECIPIENT_INFO_HPP_IENLXEUN
+#define RECIPIENT_INFO_HPP_IENLXEUN
+
+#include <vanetza/security/v2/basic_elements.hpp>
+#include <vanetza/security/v2/public_key.hpp>
+#include <boost/variant/variant.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+/// EciesEncryptedKey specified in TS 103 097 v1.2.1, section 5.9
+struct EciesEncryptedKey
+{
+    EccPoint v;
+    ByteBuffer c;
+    std::array<uint8_t, 16> t;
+};
+
+/// OpaqueKey specified in TS 103 097 v1.2.1, section 5.8
+struct OpaqueKey
+{
+    ByteBuffer data;
+};
+
+/// Key specified in TS 103 097 v1.2.1, section 5.8 (in RecipientInfo)
+typedef boost::variant<EciesEncryptedKey, OpaqueKey> Key;
+
+/// RecipientInfo specified in TS 103 097 v1.2.1, section 5.8
+struct RecipientInfo
+{
+    HashedId8 cert_id;
+    Key enc_key;
+
+    PublicKeyAlgorithm pk_encryption() const;
+};
+
+/**
+ * \brief Determines applicable PublicKeyAlgorithm
+ * \param key Algorithm has to fit this kind of key
+ * \return PublicKeyAlgorithm
+ */
+PublicKeyAlgorithm get_type(const Key&);
+
+/**
+ * Calculates size of a RecipientInfo
+ * \param info
+ * \return number of octets needed to serialize the RecipientInfo
+ */
+size_t get_size(const RecipientInfo&);
+
+/**
+ * \brief Serializes a RecipientInfo into a binary archive
+ * \param ar Destination of serialized object
+ * \param info RecipientInfo to serialize
+ * \param sym Applicable symmetric algorithm
+ */
+void serialize(OutputArchive&, const RecipientInfo&, SymmetricAlgorithm);
+
+/**
+ * \brief Deserialize a RecipientInfo
+ * \param ar Input starting with serialized RecipientInfo
+ * \param info Deserialized RecipientInfo
+ * \param sym Symmetric algorithm required to deserialize encrypted key
+ * \return size of the deserialized RecipientInfo in bytes
+ */
+size_t deserialize(InputArchive&, RecipientInfo&, const SymmetricAlgorithm&);
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza
+
+#endif /* RECIPIENT_INFO_HPP_IENLXEUN */