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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,137 @@
+#include <vanetza/security/exception.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
+{
+
+PublicKeyAlgorithm get_type(const PublicKey& key)
+{
+    struct public_key_visitor : public boost::static_visitor<PublicKeyAlgorithm>
+    {
+        PublicKeyAlgorithm operator()(const ecdsa_nistp256_with_sha256&)
+        {
+            return PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256;
+        }
+
+        PublicKeyAlgorithm operator()(const ecies_nistp256&)
+        {
+            return PublicKeyAlgorithm::ECIES_NISTP256;
+        }
+    };
+
+    public_key_visitor visit;
+    return boost::apply_visitor(visit, key);
+}
+
+void serialize(OutputArchive& ar, const PublicKey& key)
+{
+    struct public_key_visitor : public boost::static_visitor<>
+    {
+        public_key_visitor(OutputArchive& ar, PublicKeyAlgorithm algo) :
+            m_archive(ar), m_algo(algo)
+        {
+        }
+
+        void operator()(const ecdsa_nistp256_with_sha256& ecdsa)
+        {
+            serialize(m_archive, ecdsa.public_key, m_algo);
+        }
+
+        void operator()(const ecies_nistp256& ecies)
+        {
+            serialize(m_archive, ecies.supported_symm_alg);
+            serialize(m_archive, ecies.public_key, m_algo);
+        }
+
+        OutputArchive& m_archive;
+        PublicKeyAlgorithm m_algo;
+    };
+
+    PublicKeyAlgorithm type = get_type(key);
+    serialize(ar, type);
+    public_key_visitor visit(ar, type);
+    boost::apply_visitor(visit, key);
+}
+
+std::size_t field_size(PublicKeyAlgorithm algo)
+{
+    size_t size = 0;
+    switch (algo) {
+        case PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256:
+            size = 32;
+            break;
+        case PublicKeyAlgorithm::ECIES_NISTP256:
+            size = 32;
+            break;
+    }
+    return size;
+}
+
+std::size_t field_size(SymmetricAlgorithm algo)
+{
+    size_t size = 0;
+    switch (algo) {
+        case SymmetricAlgorithm::AES128_CCM:
+            size = 16;
+            break;
+        default:
+            throw deserialization_error("Unknown SymmetricAlgorithm");
+            break;
+    }
+    return size;
+}
+
+size_t deserialize(InputArchive& ar, PublicKey& key)
+{
+    PublicKeyAlgorithm type;
+    deserialize(ar, type);
+    switch (type) {
+        case PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256: {
+            ecdsa_nistp256_with_sha256 ecdsa;
+            deserialize(ar, ecdsa.public_key, PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256);
+            key = ecdsa;
+            break;
+        }
+        case PublicKeyAlgorithm::ECIES_NISTP256: {
+            ecies_nistp256 ecies;
+            deserialize(ar, ecies.supported_symm_alg);
+            deserialize(ar, ecies.public_key, PublicKeyAlgorithm::ECIES_NISTP256);
+            key = ecies;
+            break;
+        }
+        default:
+            throw deserialization_error("Unknown PublicKeyAlgorithm");
+            break;
+    }
+    return get_size(key);
+}
+
+size_t get_size(const PublicKey& key)
+{
+    size_t size = sizeof(PublicKeyAlgorithm);
+    struct publicKey_visitor : public boost::static_visitor<size_t>
+    {
+        size_t operator()(ecdsa_nistp256_with_sha256 key)
+        {
+            return get_size(key.public_key);
+        }
+
+        size_t operator()(ecies_nistp256 key)
+        {
+            return get_size(key.public_key) + sizeof(key.supported_symm_alg);
+        }
+    };
+    publicKey_visitor visit;
+    size += boost::apply_visitor(visit, key);
+    return size;
+}
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza