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FLASHING.md says how to take a newer version of the colleague's tree (copy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

@@ -0,0 +1,77 @@
+#include <vanetza/common/byte_buffer.hpp>
+#include <vanetza/security/hmac.hpp>
+#include <gtest/gtest.h>
+
+using namespace vanetza::security;
+using vanetza::ByteBuffer;
+
+class HmacTest : public ::testing::Test
+{
+protected:
+    ByteBuffer data = {0x01, 0x02, 0x03, 0x04, 0x05};
+    HmacKey key = {{
+        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
+        0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
+        0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
+        0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
+    }};
+};
+
+#if defined VANETZA_WITH_OPENSSL || defined VANETZA_WITH_CRYPTOPP
+TEST_F(HmacTest, create_hmac_tag)
+{
+    KeyTag tag = create_hmac_tag(data, key);
+    KeyTag zero = {};
+    EXPECT_NE(tag, zero);
+}
+
+TEST_F(HmacTest, deterministic)
+{
+    KeyTag tag1 = create_hmac_tag(data, key);
+    KeyTag tag2 = create_hmac_tag(data, key);
+    EXPECT_EQ(tag1, tag2);
+}
+
+TEST_F(HmacTest, different_data_different_tag)
+{
+    ByteBuffer other_data = {0x05, 0x04, 0x03, 0x02, 0x01};
+    KeyTag tag1 = create_hmac_tag(data, key);
+    KeyTag tag2 = create_hmac_tag(other_data, key);
+    EXPECT_NE(tag1, tag2);
+}
+
+TEST_F(HmacTest, different_key_different_tag)
+{
+    HmacKey other_key = {};
+    KeyTag tag1 = create_hmac_tag(data, key);
+    KeyTag tag2 = create_hmac_tag(data, other_key);
+    EXPECT_NE(tag1, tag2);
+}
+#endif
+
+#if defined VANETZA_WITH_OPENSSL
+TEST_F(HmacTest, openssl)
+{
+    KeyTag tag = create_hmac_tag_openssl(data, key);
+    KeyTag zero = {};
+    EXPECT_NE(tag, zero);
+}
+#endif
+
+#if defined VANETZA_WITH_CRYPTOPP
+TEST_F(HmacTest, cryptopp)
+{
+    KeyTag tag = create_hmac_tag_cryptopp(data, key);
+    KeyTag zero = {};
+    EXPECT_NE(tag, zero);
+}
+#endif
+
+#if defined VANETZA_WITH_OPENSSL && defined VANETZA_WITH_CRYPTOPP
+TEST_F(HmacTest, openssl_and_cryptopp_match)
+{
+    KeyTag tag_openssl = create_hmac_tag_openssl(data, key);
+    KeyTag tag_cryptopp = create_hmac_tag_cryptopp(data, key);
+    EXPECT_EQ(tag_openssl, tag_cryptopp);
+}
+#endif