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176 lines
11 KiB
ReStructuredText
176 lines
11 KiB
ReStructuredText
ESP-TLS
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=======
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Overview
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--------
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The ESP-TLS component provides a simplified API interface for accessing the commonly used TLS functionality.
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It supports common scenarios like CA certification validation, SNI, ALPN negotiation, non-blocking connection among others.
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All the configuration can be specified in the ``esp_tls_cfg_t`` data structure. Once done, TLS communication can be conducted using the following APIs:
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* :cpp:func:`esp_tls_conn_new`: for opening a new TLS connection.
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* :cpp:func:`esp_tls_conn_read`: for reading from the connection.
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* :cpp:func:`esp_tls_conn_write`: for writing into the connection.
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* :cpp:func:`esp_tls_conn_destroy`: for freeing up the connection.
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Any application layer protocol like HTTP1, HTTP2 etc can be executed on top of this layer.
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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: :example:`protocols/https_request`.
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Tree structure for ESP-TLS component
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-------------------------------------
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.. highlight:: none
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::
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├── esp_tls.c
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├── esp_tls.h
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├── esp_tls_mbedtls.c
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├── esp_tls_wolfssl.c
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└── private_include
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├── esp_tls_mbedtls.h
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└── esp_tls_wolfssl.h
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The ESP-TLS component has a file :component_file:`esp-tls/esp_tls.h` which contain the public API headers for the component. Internally ESP-TLS component uses one
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of the two SSL/TLS Libraries between mbedtls and wolfssl for its operation. API specific to mbedtls are present in :component_file:`esp-tls/private_include/esp_tls_mbedtls.h` and API
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specific to wolfssl are present in :component_file:`esp-tls/private_include/esp_tls_wolfssl.h`.
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TLS Server verification
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-----------------------
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The ESP-TLS provides multiple options for TLS server verification on the client side. The ESP-TLS client can verify the server by validating the peer's server certificate or with the help of pre-shared keys. The user should select only one of the following options in the :cpp:type:`esp_tls_cfg_t` structure for TLS server verification. If no option is selected then client will return a fatal error by default at the time of the TLS connection setup.
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* **cacert_buf** and **cacert_bytes**: The CA certificate can be provided in a buffer to the :cpp:type:`esp_tls_cfg_t` structure. The ESP-TLS will use the CA certificate present in the buffer to verify the server. The following variables in :cpp:type:`esp_tls_cfg_t` structure must be set.
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* ``cacert_buf`` - pointer to the buffer which contains the CA cert.
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* ``cacert_bytes`` - size of the CA certificate in bytes.
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* **use_global_ca_store**: The ``global_ca_store`` can be initialized and set at once. Then it can be used to verify the server for all the ESP-TLS connections which have set ``use_global_ca_store = true`` in their respective :cpp:type:`esp_tls_cfg_t` structure. See API Reference section below on information regarding different API used for initializing and setting up the ``global_ca_store``.
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* **crt_bundle_attach**: The ESP x509 Certificate Bundle API provides an easy way to include a bundle of custom x509 root certificates for TLS server verification. More details can be found at :doc:`ESP x509 Certificate Bundle</api-reference/protocols/esp_crt_bundle>`
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* **psk_hint_key**: To use pre-shared keys for server verification, :ref:`CONFIG_ESP_TLS_PSK_VERIFICATION` should be enabled in the ESP-TLS menuconfig. Then the pointer to PSK hint and key should be provided to the :cpp:type:`esp_tls_cfg_t` structure. The ESP-TLS will use the PSK for server verification only when no other option regarding the server verification is selected.
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* **skip server verification**: This is an insecure option provided in the ESP-TLS for testing purpose. The option can be set by enabling :ref:`CONFIG_ESP_TLS_INSECURE` and :ref:`CONFIG_ESP_TLS_SKIP_SERVER_CERT_VERIFY` in the ESP-TLS menuconfig. When this option is enabled the ESP-TLS will skip server verification by default when no other options for server verification are selected in the :cpp:type:`esp_tls_cfg_t` structure.
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*WARNING:Enabling this option comes with a potential risk of establishing a TLS connection with a server which has a fake identity, provided that the server certificate is not provided either through API or other mechanism like ca_store etc.*
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Underlying SSL/TLS Library Options
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----------------------------------
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The ESP-TLS component has an option to use mbedtls or wolfssl as their underlying SSL/TLS library. By default only mbedtls is available and is
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used, wolfssl SSL/TLS library is available publicly at https://github.com/espressif/esp-wolfssl. The repository provides wolfssl component in binary format, it
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also provides few examples which are useful for understanding the API. Please refer the repository README.md for
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information on licensing and other options. Please see below option for using wolfssl in your project.
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.. note:: `As the library options are internal to ESP-TLS, switching the libraries will not change ESP-TLS specific code for a project.`
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How to use wolfssl with ESP-IDF
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-------------------------------
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There are two ways to use wolfssl in your project
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1) Directly add wolfssl as a component in your project with following three commands.::
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(First change directory (cd) to your project directory)
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mkdir components
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cd components
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git clone https://github.com/espressif/esp-wolfssl.git
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2) Add wolfssl as an extra component in your project.
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* Download wolfssl with::
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git clone https://github.com/espressif/esp-wolfssl.git
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* Include esp-wolfssl in ESP-IDF with setting EXTRA_COMPONENT_DIRS in CMakeLists.txt of your project as done in `wolfssl/examples <https://github.com/espressif/esp-wolfssl/tree/master/examples>`_. For reference see Optional Project variables in :doc:`build-system.</api-guides/build-system>`
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After above steps, you will have option to choose wolfssl as underlying SSL/TLS library in configuration menu of your project as follows::
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idf.py menuconfig -> ESP-TLS -> choose SSL/TLS Library -> mbedtls/wolfssl
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Comparison between mbedtls and wolfssl
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--------------------------------------
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The following table shows a typical comparison between wolfssl and mbedtls when :example:`protocols/https_request` example `(which has server authentication)` was run with both
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SSL/TLS libraries and with all respective configurations set to default.
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`(mbedtls IN_CONTENT length and OUT_CONTENT length were set to 16384 bytes and 4096 bytes respectively)`
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+---------------------+------------+-----------+
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| Property | Wolfssl | Mbedtls |
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+=====================+============+===========+
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| Total Heap Consumed | ~19 Kb | ~37 Kb |
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+---------------------+------------+-----------+
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| Task Stack Used | ~2.2 Kb | ~3.6 Kb |
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+---------------------+------------+-----------+
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| Bin size | ~858 Kb | ~736 Kb |
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+---------------------+------------+-----------+
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.. note:: `These values are subject to change with change in configuration options and version of respective libraries`.
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.. only:: esp32
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ATECC608A (Secure Element) with ESP-TLS
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--------------------------------------------------
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ESP-TLS provides support for using ATECC608A cryptoauth chip with ESP32-WROOM-32SE.
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Use of ATECC608A is supported only when ESP-TLS is used with mbedTLS as its underlying SSL/TLS stack.
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ESP-TLS uses mbedtls as its underlying TLS/SSL stack by default unless changed manually.
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.. note:: ATECC608A chip on ESP32-WROOM-32SE must be already configured and provisioned, for details refer `esp_cryptoauth_utility <https://github.com/espressif/esp-cryptoauthlib/blob/master/esp_cryptoauth_utility/README.md#esp_cryptoauth_utility>`_
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To enable the secure element support, and use it in you project for TLS connection, you will have to follow below steps
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1) Add `esp-cryptoauthlib <https://github.com/espressif/esp-cryptoauthlib>`_ in your project, for details please refer `esp-cryptoauthlib with ESP_IDF <https://github.com/espressif/esp-cryptoauthlib#how-to-use-esp-cryptoauthlib-with-esp-idf>`_
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2) Enable following menuconfig option::
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menuconfig->Component config->ESP-TLS->Use Secure Element (ATECC608A) with ESP-TLS
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3) Select type of ATECC608A chip with following option::
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menuconfig->Component config->esp-cryptoauthlib->Choose Type of ATECC608A chip
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to know more about different types of ATECC608A chips and how to obtain type of ATECC608A connected to your ESP module please visit `ATECC608A chip type <https://github.com/espressif/esp-cryptoauthlib/blob/master/esp_cryptoauth_utility/README.md#find-type-of-atecc608a-chip-connected-to-esp32-wroom32-se>`_
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4) Enable use of ATECC608A in ESP-TLS by providing following config option in `esp_tls_cfg_t`
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.. code-block:: c
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esp_tls_cfg_t cfg = {
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/* other configurations options */
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.use_secure_element = true,
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};
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.. only:: SOC_DIG_SIGN_SUPPORTED
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.. _digital-signature-with-esp-tls:
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Digital Signature with ESP-TLS
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------------------------------
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ESP-TLS provides support for using the Digital Signature (DS) with {IDF_TARGET_NAME}.
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Use of the DS for TLS is supported only when ESP-TLS is used with mbedTLS (default stack) as its underlying SSL/TLS stack.
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For more details on Digital Signature, please refer to the :doc:`Digital Signature Documentation </api-reference/peripherals/ds>`. The technical details of Digital Signature such as
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how to calculate private key parameters can be found in *{IDF_TARGET_NAME} Technical Reference Manual* > *Digital Signature (DS)* [`PDF <{IDF_TARGET_TRM_EN_URL}#digsig>`__].
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The DS peripheral must be configured before it can be used to perform Digital Signature, see `Configure the DS Peripheral` in :doc:`Digital Signature </api-reference/peripherals/ds>`.
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The DS peripheral must be initlized with the required encrypted private key parameters (obtained when the DS peripheral is configured). ESP-TLS internally initializes the DS peripheral when
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provided with the required DS context (DS parameters). Please see the below code snippet for passing the DS context to esp-tls context. The DS context passed to the esp-tls context should not be freed till the TLS connection is deleted.
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.. code-block:: c
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#include "esp_tls.h"
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esp_ds_data_ctx_t *ds_ctx;
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/* initialize ds_ctx with encrypted private key parameters, which can be read from the nvs or
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provided through the application code */
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esp_tls_cfg_t cfg = {
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.clientcert_buf = /* the client cert */,
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.clientcert_bytes = /* length of the client cert */,
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/* other configurations options */
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.ds_data = (void *)ds_ctx,
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};
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.. note:: When using Digital Signature for the TLS connection, along with the other required params, only the client cert (`clientcert_buf`) and the DS params (`ds_data`) are required and the client key (`clientkey_buf`) can be set to NULL.
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* An example of mutual authentication with the DS peripheral can be found at :example:`ssl mutual auth<protocols/mqtt/ssl_mutual_auth>` which internally uses (ESP-TLS) for the TLS connection.
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API Reference
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-------------
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.. include-build-file:: inc/esp_tls.inc
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