diff --git a/cpp_ext/decrypt_ota_file.hpp b/cpp_ext/decrypt_ota_file.hpp
new file mode 100644
index 0000000..18ebd0e
--- /dev/null
+++ b/cpp_ext/decrypt_ota_file.hpp
@@ -0,0 +1,98 @@
+namespace netcore{
+static bool read_file_all(const std::string& path, std::vector<uint8_t>& out) {
+    std::ifstream ifs(path, std::ios::binary);
+    if (!ifs) return false;
+    ifs.seekg(0, std::ios::end);
+    std::streampos size = ifs.tellg();
+    if (size <= 0) return false;
+    ifs.seekg(0, std::ios::beg);
+    out.resize(static_cast<size_t>(size));
+    if (!ifs.read(reinterpret_cast<char*>(out.data()), size)) return false;
+    return true;
+}
+
+static bool write_file_all(const std::string& path, const uint8_t* data, size_t len) {
+    std::ofstream ofs(path, std::ios::binary | std::ios::trunc);
+    if (!ofs) return false;
+    ofs.write(reinterpret_cast<const char*>(data), static_cast<std::streamsize>(len));
+    return static_cast<bool>(ofs);
+}
+
+static bool decrypt_ota_file_impl(const std::string& input_path, const std::string& output_zip_path) {
+    std::vector<uint8_t> in;
+    if (!netcore::read_file_all(input_path, in)) {
+        netcore::log_error(std::string("decrypt_ota_file: read failed: ") + input_path);
+        return false;
+    }
+
+    const size_t min_len = kOtaMagicLen + kGcmNonceLen + kGcmTagLen + 1;
+    if (in.size() < min_len) {
+        netcore::log_error("decrypt_ota_file: too short");
+        return false;
+    }
+    if (!std::equal(in.begin(), in.begin() + kOtaMagicLen, reinterpret_cast<const uint8_t*>(kOtaMagic))) {
+        netcore::log_error("decrypt_ota_file: bad magic");
+        return false;
+    }
+
+    const uint8_t* nonce = in.data() + kOtaMagicLen;
+    const uint8_t* ct_and_tag = in.data() + kOtaMagicLen + kGcmNonceLen;
+    const size_t ct_and_tag_len = in.size() - (kOtaMagicLen + kGcmNonceLen);
+    if (ct_and_tag_len <= kGcmTagLen) {
+        netcore::log_error("decrypt_ota_file: no ciphertext");
+        return false;
+    }
+    const size_t ciphertext_len = ct_and_tag_len - kGcmTagLen;
+    const uint8_t* ciphertext = ct_and_tag;
+    const uint8_t* tag = ct_and_tag + ciphertext_len;
+
+    std::vector<uint8_t> plain(ciphertext_len);
+    int out_len1 = 0;
+    int out_len2 = 0;
+
+    EVP_CIPHER_CTX* ctx = EVP_CIPHER_CTX_new();
+    if (!ctx) {
+        netcore::log_error("decrypt_ota_file: EVP_CIPHER_CTX_new failed");
+        return false;
+    }
+
+    bool ok = false;
+    auto key = ota_key_bytes();
+
+    do {
+        if (1 != EVP_DecryptInit_ex(ctx, EVP_aes_256_gcm(), nullptr, nullptr, nullptr)) {
+            netcore::log_error("decrypt_ota_file: DecryptInit failed");
+            break;
+        }
+        if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_IVLEN, static_cast<int>(kGcmNonceLen), nullptr)) {
+            netcore::log_error("decrypt_ota_file: set ivlen failed");
+            break;
+        }
+        if (1 != EVP_DecryptInit_ex(ctx, nullptr, nullptr, key.data(), nonce)) {
+            netcore::log_error("decrypt_ota_file: set key/iv failed");
+            break;
+        }
+        if (1 != EVP_DecryptUpdate(ctx, plain.data(), &out_len1, ciphertext, static_cast<int>(ciphertext_len))) {
+            netcore::log_error("decrypt_ota_file: update failed");
+            break;
+        }
+        if (1 != EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, static_cast<int>(kGcmTagLen), const_cast<uint8_t*>(tag))) {
+            netcore::log_error("decrypt_ota_file: set tag failed");
+            break;
+        }
+        if (1 != EVP_DecryptFinal_ex(ctx, plain.data() + out_len1, &out_len2)) {
+            netcore::log_error("decrypt_ota_file: final failed (auth tag mismatch?)");
+            break;
+        }
+        const size_t plain_len = static_cast<size_t>(out_len1 + out_len2);
+        if (!netcore::write_file_all(output_zip_path, plain.data(), plain_len)) {
+            netcore::log_error(std::string("decrypt_ota_file: write failed: ") + output_zip_path);
+            break;
+        }
+        ok = true;
+    } while (false);
+
+    EVP_CIPHER_CTX_free(ctx);
+    return ok;
+}
+}
\ No newline at end of file
diff --git a/cpp_ext/msg_handler.cpp b/cpp_ext/msg_handler.cpp
new file mode 100644
index 0000000..e69de29
diff --git a/cpp_ext/utils.cpp b/cpp_ext/utils.cpp
new file mode 100644
index 0000000..e69de29
diff --git a/cpp_ext/utils.hpp b/cpp_ext/utils.hpp
new file mode 100644
index 0000000..e69de29