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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,161 @@
+#include <vanetza/security/exception.hpp>
+#include <vanetza/security/v2/signature.hpp>
+#include <boost/iostreams/stream.hpp>
+#include <cassert>
+
+namespace vanetza
+{
+namespace security
+{
+namespace v2
+{
+
+PublicKeyAlgorithm get_type(const Signature& sig)
+{
+    struct Signature_visitor : public boost::static_visitor<PublicKeyAlgorithm>
+    {
+        PublicKeyAlgorithm operator()(const EcdsaSignature&)
+        {
+            return PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256;
+        }
+
+        PublicKeyAlgorithm operator()(const EcdsaSignatureFuture&)
+        {
+            return PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256;
+        }
+    };
+    Signature_visitor visit;
+    return boost::apply_visitor(visit, sig.some_ecdsa);
+}
+
+size_t get_size(const EcdsaSignature& sig)
+{
+    size_t size = sig.s.size();
+    size += get_size(sig.R);
+    return size;
+}
+
+size_t get_size(const EcdsaSignatureFuture& sig)
+{
+    return sig.size();
+}
+
+size_t get_size(const Signature& sig)
+{
+    size_t size = sizeof(PublicKeyAlgorithm);
+    struct Signature_visitor : public boost::static_visitor<size_t>
+    {
+        size_t operator()(const EcdsaSignature& sig)
+        {
+            return get_size(sig);
+        }
+
+        size_t operator()(const EcdsaSignatureFuture& sig)
+        {
+            return get_size(sig);
+        }
+    };
+    Signature_visitor visit;
+    size += boost::apply_visitor(visit, sig.some_ecdsa);
+    return size;
+}
+
+void serialize(OutputArchive& ar, const Signature& sig)
+{
+    struct signature_visitor : public boost::static_visitor<>
+    {
+        signature_visitor(OutputArchive& ar) : m_archive(ar) {}
+
+        void operator()(const EcdsaSignature& sig)
+        {
+            serialize(m_archive, sig);
+        }
+
+        void operator()(const EcdsaSignatureFuture& sig)
+        {
+            serialize(m_archive, sig);
+        }
+
+        OutputArchive& m_archive;
+    };
+
+    PublicKeyAlgorithm algo = get_type(sig);
+    serialize(ar, algo);
+    signature_visitor visitor(ar);
+    boost::apply_visitor(visitor, sig.some_ecdsa);
+}
+
+void serialize(OutputArchive& ar, const EcdsaSignature& sig)
+{
+    const PublicKeyAlgorithm algo = PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256;
+    assert(field_size(algo) == sig.s.size());
+
+    serialize(ar, sig.R, algo);
+    for (auto& byte : sig.s) {
+        ar << byte;
+    }
+}
+
+void serialize(OutputArchive& ar, const EcdsaSignatureFuture& sig)
+{
+    auto& ecdsa = sig.get();
+    serialize(ar, ecdsa);
+}
+
+size_t deserialize(InputArchive& ar, EcdsaSignature& sig, const PublicKeyAlgorithm& algo)
+{
+    EccPoint point;
+    ByteBuffer buf;
+    deserialize(ar, point, algo);
+    for (size_t i = 0; i < field_size(algo); i++) {
+        uint8_t byte;
+        ar >> byte;
+        buf.push_back(byte);
+    }
+    sig.R = point;
+    sig.s = buf;
+    return get_size(sig);
+}
+
+size_t deserialize(InputArchive& ar, Signature& sig)
+{
+    PublicKeyAlgorithm algo;
+    size_t size = 0;
+    deserialize(ar, algo);
+    size += sizeof(algo);
+    switch (algo) {
+        case PublicKeyAlgorithm::ECDSA_NISTP256_With_SHA256: {
+            EcdsaSignature signature;
+            size += deserialize(ar, signature, algo);
+            sig = signature;
+            break;
+        }
+        default:
+            throw deserialization_error("Unknown PublicKeyAlgorithm");
+    }
+    return size;
+}
+
+boost::optional<EcdsaSignature> extract_ecdsa_signature(const Signature& sig)
+{
+    struct signature_visitor : public boost::static_visitor<const EcdsaSignature*>
+    {
+        const EcdsaSignature* operator()(const EcdsaSignature& sig)
+        {
+            return &sig;
+        }
+
+        const EcdsaSignature* operator()(const EcdsaSignatureFuture& sig)
+        {
+            return &sig.get();
+        }
+    };
+
+    signature_visitor visitor;
+    const EcdsaSignature* ecdsa = boost::apply_visitor(visitor, sig.some_ecdsa);
+    return boost::optional<EcdsaSignature>(ecdsa != nullptr, *ecdsa);
+}
+
+} // namespace v2
+} // namespace security
+} // namespace vanetza