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FLASHING.md says how to take a newer version of the colleague's tree (copy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).

microbu-esp32c5/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 */