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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,91 @@
+#include <vanetza/security/exception.hpp>
+#include <vanetza/security/v2/encryption_parameter.hpp>
+#include <vanetza/security/v2/public_key.hpp>
+#include <boost/variant/apply_visitor.hpp>
+#include <boost/variant/static_visitor.hpp>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+SymmetricAlgorithm get_type(const EncryptionParameter& param)
+{
+    struct Encryption_visitor : public boost::static_visitor<SymmetricAlgorithm>
+    {
+        SymmetricAlgorithm operator()(const Nonce&)
+        {
+            return SymmetricAlgorithm::AES128_CCM;
+        }
+    };
+
+    Encryption_visitor visit;
+    return boost::apply_visitor(visit, param);
+}
+
+void serialize(OutputArchive& ar, const EncryptionParameter& param)
+{
+    struct Encryption_visitor : public boost::static_visitor<>
+    {
+        Encryption_visitor(OutputArchive& ar) :
+            m_archive(ar)
+        {
+        }
+
+        void operator()(const Nonce& nonce)
+        {
+            for (auto& byte : nonce) {
+                m_archive << byte;
+            }
+        }
+
+        OutputArchive& m_archive;
+    };
+
+    SymmetricAlgorithm algo = get_type(param);
+    serialize(ar, algo);
+    Encryption_visitor visit(ar);
+    boost::apply_visitor(visit, param);
+}
+
+size_t get_size(const EncryptionParameter& param)
+{
+    size_t size = sizeof(SymmetricAlgorithm);
+    struct Encryption_visitor : public boost::static_visitor<size_t>
+    {
+        size_t operator()(const Nonce& nonce)
+        {
+            return nonce.size();
+        }
+    };
+
+    Encryption_visitor visit;
+    size += boost::apply_visitor(visit, param);
+    return size;
+}
+
+size_t deserialize(InputArchive& ar, EncryptionParameter& param)
+{
+    SymmetricAlgorithm algo;
+    deserialize(ar, algo);
+    switch (algo) {
+        case SymmetricAlgorithm::AES128_CCM: {
+            Nonce nonce;
+            for (size_t s = 0; s < nonce.size(); s++) {
+                ar >> nonce[s];
+            }
+            param = nonce;
+            break;
+        }
+        default:
+            throw deserialization_error("Unknown Symmetric Algorithm");
+            break;
+    }
+    return get_size(param);
+}
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza