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FLASHING.md says how to take a newer version of the colleague's tree (copy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/tools/pki/encrypted_data.hpp

@@ -0,0 +1,51 @@
+#pragma once
+
+#include "security_module.hpp"
+#include <vanetza/asn1/asn1c_wrapper.hpp>
+#include <vanetza/asn1/security/EtsiTs103097Data-Encrypted.h>
+
+namespace vanetza
+{
+namespace pki
+{
+
+// forward declarations
+struct HashedId8;
+class SecurityModule;
+
+class EncryptedData : public asn1::asn1c_oer_wrapper<Vanetza_Security_EtsiTs103097Data_Encrypted_85P0_t>
+{
+public:
+    using wrapper = asn1::asn1c_oer_wrapper<Vanetza_Security_EtsiTs103097Data_Encrypted_85P0_t>;
+
+    EncryptedData(std::shared_ptr<SecurityModule::EciesContext> ecies);
+    void generate_ciphertext(const ByteBuffer& payload);
+    void add_recipient_info(const HashedId8&);
+    const OCTET_STRING_t* get_nonce() const;
+    const OCTET_STRING_t* get_ciphertext() const;
+
+    /**
+     * \brief Decrypt a PKI response that reuses the request's symmetric AES key.
+     *
+     * Call on the same EncryptedData instance that built the request, after
+     * decode()-ing the response body into it. The AA/EA encrypts its response
+     * with the request's AES key referenced via pskRecipInfo
+     * (TS 102 941 §6.2.3.3.2 for AT, §6.2.3.2.2 for EC).
+     * \throws DecodingFailure if the ciphertext or pskRecipInfo is missing
+     */
+    ByteBuffer decrypt();
+
+    // Lower-level builders that mutate an EtsiTs103097Data-Encrypted value in-place
+    static void init(asn1c_type& dest);
+    static void set_aes_ccm_ciphertext(asn1c_type& dest, SecurityModule::EciesContext& ecies,
+        const ByteBuffer& plaintext);
+    static void append_recipient_info(asn1c_type& dest, const SecurityModule::EciesContext& ecies,
+        const HashedId8& recipient);
+
+private:
+    bool has_psk_recipient() const;
+    std::shared_ptr<SecurityModule::EciesContext> m_ecies;
+};
+
+} // namespace pki
+} // namespace vanetza