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83 lines
4.1 KiB
ReStructuredText
83 lines
4.1 KiB
ReStructuredText
ESP x509 Certificate Bundle
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===========================
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Overview
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--------
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The ESP x509 Certificate Bundle API provides an easy way to include a bundle of custom x509 root certificates for TLS server verification.
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.. note:: The bundle is currently not available when using WolfSSL.
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The bundle comes with the complete list of root certificates from Mozilla’s NSS root certificate store. Using the gen_crt_bundle.py python utility the certificates’ subject name and public key are stored in a file and embedded in the {IDF_TARGET_NAME} binary.
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When generating the bundle you may choose between:
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* The full root certificate bundle from Mozilla, containing more than 130 certificates. The current bundle was updated Tue Apr 26 03:12:05 2022 GMT.
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* A pre-selected filter list of the name of the most commonly used root certificates, reducing the amount of certificates to around 35 while still having around 90 % coverage according to market share statistics.
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In addition it is possible to specify a path to a certificate file or a directory containing certificates which then will be added to the generated bundle.
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.. note:: Trusting all root certificates means the list will have to be updated if any of the certificates are retracted. This includes removing them from `cacrt_all.pem`.
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Configuration
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-------------
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Most configuration is done through menuconfig. Make and CMake will generate the bundle according to the configuration and embed it.
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* :ref:`CONFIG_MBEDTLS_CERTIFICATE_BUNDLE`: automatically build and attach the bundle.
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* :ref:`CONFIG_MBEDTLS_DEFAULT_CERTIFICATE_BUNDLE`: decide which certificates to include from the complete root list.
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* :ref:`CONFIG_MBEDTLS_CUSTOM_CERTIFICATE_BUNDLE_PATH`: specify the path of any additional certificates to embed in the bundle.
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To enable the bundle when using ESP-TLS simply pass the function pointer to the bundle attach function:
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.. code:: c
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esp_tls_cfg_t cfg = {
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.crt_bundle_attach = esp_crt_bundle_attach,
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};
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This is done to avoid embedding the certificate bundle unless activated by the user.
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If using mbedTLS directly then the bundle may be activated by directly calling the attach function during the setup process:
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.. code:: c
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mbedtls_ssl_config conf;
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mbedtls_ssl_config_init(&conf);
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esp_crt_bundle_attach(&conf);
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Generating the List of Root Certificates
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----------------------------------------
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The list of root certificates comes from Mozilla's NSS root certificate store, which can be found `here <https://wiki.mozilla.org/CA/Included_Certificates>`_
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The list can be downloaded and created by running the script ``mk-ca-bundle.pl`` that is distributed as a part of `curl <https://github.com/curl/curl>`_.
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Another alternative would be to download the finished list directly from the curl website: `CA certificates extracted from Mozilla <https://curl.haxx.se/docs/caextract.html>`_
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The common certificates bundle were made by selecting the authorities with a market share of more than 1 % from w3tech's `SSL Survey <https://w3techs.com/technologies/overview/ssl_certificate/all>`_.
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These authorities were then used to pick the names of the certificates for the filter list, `cmn_crt_authorities.csv`, from `this list <https://ccadb-public.secure.force.com/mozilla/IncludedCACertificateReportPEMCSV>`_ provided by Mozilla.
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.. _updating_bundle:
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Updating the Certificate Bundle
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-------------------------------
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The bundle is embedded into the app and can be updated along with the app by an OTA update. If you want to include a more up-to-date bundle than the bundle currently included in IDF, then the certificate list can be downloaded from Mozilla as described in :ref:`updating_bundle`.
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Application Example
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-------------------
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Simple HTTPS example that uses ESP-TLS to establish a secure socket connection using the certificate bundle with two custom certificates added for verification: :example:`protocols/https_x509_bundle`.
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HTTPS example that uses ESP-TLS and the default bundle: :example:`protocols/https_request`.
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HTTPS example that uses mbedTLS and the default bundle: :example:`protocols/https_mbedtls`.
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API Reference
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-------------
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.. include-build-file:: inc/esp_crt_bundle.inc
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