# ESP-TLS

[中文]

## Overview

The ESP-TLS component provides a simplified API interface for accessing the commonly used TLS functions. It supports common scenarios like CA certification validation, SNI, ALPN negotiation, and non-blocking connection among others. All the configurations can be specified in the `esp_tls_cfg_t` data structure. Once done, TLS communication can be conducted using the following APIs:

> - `esp_tls_init()`: for initializing the TLS connection handle.

> - `esp_tls_conn_new_sync()`: for opening a new blocking TLS connection.

> - `esp_tls_conn_new_async()`: for opening a new non-blocking TLS connection.

> - `esp_tls_conn_read()`: for reading from the connection.

> - `esp_tls_conn_write()`: for writing into the connection.

> - `esp_tls_conn_destroy()`: for freeing up the connection.

Any application layer protocol like HTTP1, HTTP2, etc can be executed on top of this layer.

## Application Example

Simple HTTPS example that uses ESP-TLS to establish a secure socket connection: protocols/https_request.

## Tree Structure for ESP-TLS Component

    ├── esp_tls.c
    ├── esp_tls.h
    ├── esp_tls_mbedtls.c
    ├── esp_tls_wolfssl.c
    └── private_include
        ├── esp_tls_mbedtls.h
        └── esp_tls_wolfssl.h

The ESP-TLS component has a file esp-tls/esp_tls.h which contains the public API headers for the component. Internally, the ESP-TLS component operates using either MbedTLS or WolfSSL, which are SSL/TLS libraries. APIs specific to MbedTLS are present in esp-tls/private_include/esp_tls_mbedtls.h and APIs specific to WolfSSL are present in esp-tls/private_include/esp_tls_wolfssl.h.

## TLS Server Verification

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 `esp_tls_cfg_t` structure for TLS server verification. If no option is selected, the client will return a fatal error by default during the TLS connection setup.

> - cacert_buf and cacert_bytes: The CA certificate can be provided in a buffer to the `esp_tls_cfg_t` structure. The ESP-TLS uses the CA certificate present in the buffer to verify the server. The following variables in the `esp_tls_cfg_t` structure must be set.

>   > - `cacert_buf` - pointer to the buffer which contains the CA certification.

>   > - `cacert_bytes` - the size of the CA certificate in bytes.

> - 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 `esp_tls_cfg_t` structure. See the API Reference section below for information regarding different APIs used for initializing and setting up the `global_ca_store`.

> - 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 ESP x509 Certificate Bundle.

> - psk_hint_key: To use pre-shared keys for server verification, CONFIG_ESP_TLS_PSK_VERIFICATION should be enabled in the ESP-TLS menuconfig. Then the pointer to the PSK hint and key should be provided to the `esp_tls_cfg_t` structure. The ESP-TLS will use the PSK for server verification only when no other option regarding server verification is selected.

> - skip server verification: This is an insecure option provided in the ESP-TLS for testing purposes. The option can be set by enabling CONFIG_ESP_TLS_INSECURE and 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 `esp_tls_cfg_t` structure.

>   Warning

>   If this option is enabled, there is a risk of establishing a TLS connection with a server that has a fake identity, unless the server certificate is provided through the API or other mechanisms like `ca_store`.

## SNI (Server Name Indication)

SNI is an extension to the TLS protocol that allows the client to specify the hostname it is connecting to during the TLS handshake. This is required when connecting to servers that host multiple domains on the same IP address.

How to ensure SNI works properly:

- SNI is enabled by default in ESP-TLS when using HTTPS connections.

- To explicitly set the SNI hostname, use the `common_name` field in `esp_tls_cfg_t`. This ensures that the correct hostname is sent to the server during the handshake.

- The value of `common_name` must match the server certificate's CN (Common Name).

- The `skip_common_name` field should be set to `false` to ensure the server certificate is properly validated against the hostname. This is required for SNI to function correctly.

Example:

    esp_tls_cfg_t cfg = {
        .cacert_buf = ...,
        .cacert_bytes = ...,
        .common_name = "example.com", // SNI hostname
        .skip_common_name = false,    // Ensure certificate is validated
    };

## ESP-TLS Server Cert Selection Hook

The ESP-TLS component provides an option to set the server certification selection hook when using the MbedTLS stack. This provides an ability to configure and use a certificate selection callback during server handshake. The callback helps to select a certificate to present to the client based on the TLS extensions supplied in the client hello message, such as ALPN and SNI. To enable this feature, please enable CONFIG_ESP_TLS_SERVER_CERT_SELECT_HOOK in the ESP-TLS menuconfig.

The certificate selection callback can be configured in the `esp_tls_cfg_t` structure as follows:

    int cert_selection_callback(mbedtls_ssl_context *ssl)
    {
        /* Code that the callback should execute */
        return 0;
    }

    esp_tls_cfg_t cfg = {
        cert_select_cb = cert_section_callback,
    };

## Underlying SSL/TLS Library Options

The ESP-TLS component offers the option to use MbedTLS or WolfSSL as its underlying SSL/TLS library. By default, only MbedTLS is available and used, WolfSSL SSL/TLS library is also available publicly at https://github.com/espressif/esp-wolfssl. The repository provides the WolfSSL component in binary format, and it also provides a few examples that are useful for understanding the API. Please refer to the repository `README.md` for information on licensing and other options. Please see the below section for instructions on how to use WolfSSL in your project.

Note

As the library options are internal to ESP-TLS, switching the libraries will not change ESP-TLS specific code for a project.

## How to Use WolfSSL with ESP-IDF

There are two ways to use WolfSSL in your project:

- Add WolfSSL as a component directly to your project. For this, go to your project directory and run:

      mkdir components
      cd components
      git clone --recursive https://github.com/espressif/esp-wolfssl.git

- Add WolfSSL as an extra component in your project.

  > 1. Download WolfSSL with:

  >        git clone --recursive https://github.com/espressif/esp-wolfssl.git

  > 2. Include ESP-WolfSSL in ESP-IDF with setting `EXTRA_COMPONENT_DIRS` in `CMakeLists.txt` of your project as done in wolfssl/examples. For reference see Optional Project Variables in build-system.

After the above steps, you will have the option to choose WolfSSL as the underlying SSL/TLS library in the configuration menu of your project as follow:

    idf.py menuconfig > ESP-TLS > SSL/TLS Library > Mbedtls/Wolfssl

## Comparison Between MbedTLS and WolfSSL

The following table shows a typical comparison between WolfSSL and MbedTLS when the protocols/https_request example (which includes server authentication) is running with both SSL/TLS libraries and with all respective configurations set to default. For MbedTLS, the IN_CONTENT length and OUT_CONTENT length are set to 16384 bytes and 4096 bytes respectively.

Property | WolfSSL | MbedTLS
--- | --- | ---
Total Heap Consumed | ~ 19 KB | ~ 37 KB
Task Stack Used | ~ 2.2 KB | ~ 3.6 KB
Bin size | ~ 858 KB | ~ 736 KB

Note

These values can vary based on configuration options and version of respective libraries.

## ATECC608A (Secure Element) with ESP-TLS

ESP-TLS provides support for using ATECC608A cryptoauth chip with ESP32 series of SoCs. The use of ATECC608A is supported only when ESP-TLS is used with MbedTLS as its underlying SSL/TLS stack. ESP-TLS uses MbedTLS as its underlying TLS/SSL stack by default unless changed manually.

Note

ATECC608A chip interfaced to ESP32 series must be already configured. For details, please refer to esp_cryptoauth_utility.

To enable the secure element support, and use it in your project for TLS connection, you have to follow the below steps:

1. Add esp-cryptoauthlib in your project, for details please refer how to use esp-cryptoauthlib with ESP-IDF.

2. Enable the menuconfig option CONFIG_ESP_TLS_USE_SECURE_ELEMENT:

       menuconfig > Component config > ESP-TLS > Use Secure Element (ATECC608A) with ESP-TLS

3. Select type of ATECC608A chip with following option:

       menuconfig > Component config > esp-cryptoauthlib > Choose Type of ATECC608A chip

   To know more about different types of ATECC608A chips and how to obtain the type of ATECC608A connected to your ESP module, please visit ATECC608A chip type.

4. Enable the use of ATECC608A in ESP-TLS by providing the following config option in `esp_tls_cfg_t`:

       esp_tls_cfg_t cfg = {
           /* other configurations options */
           .use_secure_element = true,
       };

## Digital Signature with ESP-TLS

ESP-TLS provides support for using the Digital Signature (DS) with ESP32-C6. Use of the DS for TLS is supported only when ESP-TLS is used with MbedTLS (default stack) as its underlying SSL/TLS stack. For more details on Digital Signature, please refer to the Digital Signature (DS). The technical details of Digital Signature such as how to calculate private key parameters can be found in ESP32-C6 Technical Reference Manual > Digital Signature (DS) [PDF]. The DS peripheral must be configured before it can be used to perform Digital Signature, see Configure the DS Peripheral for a TLS Connection.

The DS peripheral must be initialized with the required encrypted private key parameters, which are obtained when the DS peripheral is configured. ESP-TLS internally initializes the DS peripheral when provided with the required DS context, i.e., DS parameters. Please see the below code snippet for passing the DS context to the ESP-TLS context. The DS context passed to the ESP-TLS context should not be freed till the TLS connection is deleted.

    #include "esp_tls.h"
    esp_ds_data_ctx_t *ds_ctx;
    /* initialize ds_ctx with encrypted private key parameters, which can be read from the nvs or provided through the application code */
    esp_tls_cfg_t cfg = {
        .clientcert_buf = /* the client certification */,
        .clientcert_bytes = /* length of the client certification */,
        /* other configurations options */
        .ds_data = (void *)ds_ctx,
    };

Note

When using Digital Signature for the TLS connection, along with the other required params, only the client certification (clientcert_buf) and the DS params (ds_data) are required and the client key (clientkey_buf) can be set to NULL.

- An example of mutual authentication with the DS peripheral can be found at ssl mutual auth which internally uses (ESP-TLS) for the TLS connection.

## Client Session Tickets

ESP-TLS supports client-side session resumption, which can significantly reduce the time and resources spent on full TLS handshakes for subsequent connections to the same server. This feature is available when ESP-TLS uses MbedTLS as its underlying SSL/TLS stack.

The mechanism for session resumption differs slightly between TLS versions:

- TLS 1.2: Session resumption can be achieved using session IDs (managed internally by the TLS stack) or session tickets (as per RFC 5077). ESP-TLS focuses on the session ticket mechanism for explicit application control.

- TLS 1.3: Session resumption is accomplished exclusively through session tickets, which are sent by the server via a "NewSessionTicket" message after the main handshake is complete. Unlike TLS 1.2, these tickets can be sent at any time during the session, not just immediately after the handshake.

To enable and use client session tickets:

1. Enable the Kconfig option CONFIG_ESP_TLS_CLIENT_SESSION_TICKETS.

2. After a successful TLS connection (and handshake completion), retrieve the session ticket using `esp_tls_get_client_session()`.

   > - For TLS 1.3: Since session tickets can arrive from the server at any point after the handshake, an application might need to call `esp_tls_get_client_session()` periodically or after specific application-level exchanges if it wants to ensure it has the most recent ticket. Each new ticket received and processed by the TLS stack supersedes the previous one for future resumption attempts.

3. Store this session ticket securely.

4. For subsequent connections to the same server, provide the stored session ticket in the `esp_tls_cfg_t::client_session` field.

5. Remember to free the client session context using `esp_tls_free_client_session()` when it's no longer needed or before obtaining a new one.

    #include "esp_tls.h"

    // Global or persistent storage for the client session
    esp_tls_client_session_t *saved_session = NULL;

    void connect_to_server(bool use_saved_session_arg) {
        esp_tls_cfg_t cfg = {0}; // Initialize other config parameters as needed
        // ... set other cfg members like cacert_buf, common_name etc. ...

        if (use_saved_session_arg && saved_session) {
            cfg.client_session = saved_session;
            // ESP_LOGI(TAG, "Attempting connection with saved session ticket.");
        } else {
            // ESP_LOGI(TAG, "Attempting connection without a saved session ticket (full handshake).");
        }

        esp_tls_t *tls = esp_tls_init();
        if (!tls) {
            // ESP_LOGE(TAG, "Failed to initialize ESP-TLS handle.");
            return;
        }

        if (esp_tls_conn_http_new_sync("https://your-server.com", &cfg, tls) == 1) {
            // ESP_LOGI(TAG, "Connection successful.");

            // Always try to get/update the session ticket to have the latest one.
            // This is beneficial whether the connection was a new handshake or a resumption,
            // especially for TLS 1.3 where new tickets can arrive post-handshake.
            if (saved_session) {
                esp_tls_free_client_session(saved_session); // Free previous session if any
                saved_session = NULL;
            }
            saved_session = esp_tls_get_client_session(tls);
            if (saved_session) {
                // ESP_LOGI(TAG, "Successfully retrieved/updated client session ticket.");
            } else {
                // ESP_LOGW(TAG, "Failed to get client session ticket even after a successful connection.");
            }

            // ... do TLS communication ...

        }
        esp_tls_conn_destroy(tls);
    }

Note

- The session ticket obtained from a server is typically valid for a limited time. The server dictates this lifetime.

- When attempting a connection using a stored session ticket, if the ticket is found to be invalid by the server (e.g., it has expired or is otherwise rejected), ESP-TLS will automatically attempt to perform a full TLS handshake to establish the connection. The application does not need to implement separate logic to retry the connection without the ticket in this scenario. A connection failure will only be reported if both the session resumption and the subsequent internal attempt at a full handshake are unsuccessful.

- The `esp_tls_client_session_t` context should be freed using `esp_tls_free_client_session()` when it is no longer needed, or before a new session is obtained and stored in the same pointer.

- For TLS 1.3, be mindful that the server can send multiple NewSessionTicket messages during a connection. Each successful call to `esp_tls_get_client_session()` will provide the context of the latest ticket processed by the underlying TLS stack. It is the application's responsibility to manage and update its stored session if it wishes to use the newest tickets for resumption.

## TLS Ciphersuites

ESP-TLS provides the ability to set a ciphersuites list in client mode. The TLS ciphersuites list informs the server about the supported ciphersuites for the specific TLS connection regardless of the TLS stack configuration. If the server supports any ciphersuite from this list, then the TLS connection will succeed; otherwise, it will fail.

You can set `ciphersuites_list` in the `esp_tls_cfg_t` structure during client connection as follows:

    /* ciphersuites_list must end with 0 and must be available in the memory scope active during the entire TLS connection */
    static const int ciphersuites_list[] = {MBEDTLS_TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384, MBEDTLS_TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, 0};
    esp_tls_cfg_t cfg = {
        .ciphersuites_list = ciphersuites_list,
    };

ESP-TLS will not check the validity of `ciphersuites_list` that was set, you should call `esp_tls_get_ciphersuites_list()` to get ciphersuites list supported in the TLS stack and cross-check it against the supplied list.

Note

This feature is supported only in the MbedTLS stack.

## TLS Protocol Version

ESP-TLS provides the ability to set the TLS protocol version for the respective TLS connection. Once the version is specified, it should be exclusively used to establish the TLS connection. This provides an ability to route different TLS connections to different protocol versions like TLS 1.2 and TLS 1.3 at runtime.

Note

At the moment, the feature is supported only when ESP-TLS is used with MbedTLS as its underlying SSL/TLS stack.

To set TLS protocol version with ESP-TLS, set `esp_tls_cfg_t::tls_version` to the required protocol version from `esp_tls_proto_ver_t`. If the protocol version field is not set, then the default policy is to allow TLS connection based on the server requirement.

The ESP-TLS connection can be configured to use the specified protocol version as follows:

    #include "esp_tls.h"
    esp_tls_cfg_t cfg = {
        .tls_version = ESP_TLS_VER_TLS_1_2,
    };

## API Reference

### Header File

- components/esp-tls/esp_tls.h

- This header file can be included with:

  >     #include "esp_tls.h"

- This header file is a part of the API provided by the `esp-tls` component. To declare that your component depends on `esp-tls`, add the following to your CMakeLists.txt:

  >     REQUIRES esp-tls

  > or

  >     PRIV_REQUIRES esp-tls

### Functions

esp_err_t esp_tls_cfg_server_session_tickets_init(esp_tls_cfg_server_t *cfg)

  Initialize the server side TLS session ticket context.

  This function initializes the server side tls session ticket context which holds all necessary data structures to enable tls session tickets according to RFC5077. Use esp_tls_cfg_server_session_tickets_free to free the data.

  Parameters:

    cfg -- [in] server configuration as esp_tls_cfg_server_t

  Returns:

    ESP_OK if setup succeeded ESP_ERR_INVALID_ARG if context is already initialized ESP_ERR_NO_MEM if memory allocation failed ESP_ERR_NOT_SUPPORTED if session tickets are not available due to build configuration ESP_FAIL if setup failed

void esp_tls_cfg_server_session_tickets_free(esp_tls_cfg_server_t *cfg)

  Free the server side TLS session ticket context.

  Parameters:

    cfg -- server configuration as esp_tls_cfg_server_t

esp_tls_t *esp_tls_init(void)

  Create TLS connection.

  This function allocates and initializes esp-tls structure handle.

  Returns:

    tls Pointer to esp-tls as esp-tls handle if successfully initialized, NULL if allocation error

int esp_tls_conn_new_sync(const char *hostname, int hostlen, int port, const esp_tls_cfg_t *cfg, esp_tls_t *tls)

  Create a new blocking TLS/SSL connection.

  This function establishes a TLS/SSL connection with the specified host in blocking manner.

  Parameters:

    - hostname -- [in] Hostname of the host.

    - hostlen -- [in] Length of hostname.

    - port -- [in] Port number of the host.

    - cfg -- [in] TLS configuration as esp_tls_cfg_t. For a TLS connection, pass a pointer to a esp_tls_cfg_t. For a plain TCP connection, pass a pointer to a esp_tls_cfg_t with is_plain_tcp set to true. At a minimum, this pointer should be not NULL and the structure should be zero-initialized

    - tls -- [in] Pointer to esp-tls as esp-tls handle.

  Returns:

    - -1 If connection establishment fails.

    - 1 If connection establishment is successful.

    - 0 If connection state is in progress.

int esp_tls_conn_http_new_sync(const char *url, const esp_tls_cfg_t *cfg, esp_tls_t *tls)

  Create a new blocking TLS/SSL connection with a given "HTTP" url.

  The behaviour is same as esp_tls_conn_new_sync() API. However this API accepts host's url.

  Parameters:

    - url -- [in] url of host.

    - cfg -- [in] TLS configuration as esp_tls_cfg_t. If you wish to open non-TLS connection, keep this NULL. For TLS connection, a pass pointer to 'esp_tls_cfg_t'. At a minimum, this structure should be zero-initialized.

    - tls -- [in] Pointer to esp-tls as esp-tls handle.

  Returns:

    - -1 If connection establishment fails.

    - 1 If connection establishment is successful.

    - 0 If connection state is in progress.

int esp_tls_conn_new_async(const char *hostname, int hostlen, int port, const esp_tls_cfg_t *cfg, esp_tls_t *tls)

  Create a new non-blocking TLS/SSL connection.

  This function initiates a non-blocking TLS/SSL connection with the specified host, but due to its non-blocking nature, it doesn't wait for the connection to get established.

  Parameters:

    - hostname -- [in] Hostname of the host.

    - hostlen -- [in] Length of hostname.

    - port -- [in] Port number of the host.

    - cfg -- [in] TLS configuration as esp_tls_cfg_t. `non_block` member of this structure should be set to be true.

    - tls -- [in] pointer to esp-tls as esp-tls handle.

  Returns:

    - -1 If connection establishment fails.

    - 0 If connection establishment is in progress.

    - 1 If connection establishment is successful.

int esp_tls_conn_http_new_async(const char *url, const esp_tls_cfg_t *cfg, esp_tls_t *tls)

  Create a new non-blocking TLS/SSL connection with a given "HTTP" url.

  The behaviour is same as esp_tls_conn_new_async() API. However this API accepts host's url.

  Parameters:

    - url -- [in] url of host.

    - cfg -- [in] TLS configuration as esp_tls_cfg_t.

    - tls -- [in] pointer to esp-tls as esp-tls handle.

  Returns:

    - -1 If connection establishment fails.

    - 0 If connection establishment is in progress.

    - 1 If connection establishment is successful.

ssize_t esp_tls_conn_write(esp_tls_t *tls, const void *data, size_t datalen)

  Write from buffer 'data' into specified tls connection.

  Parameters:

    - tls -- [in] pointer to esp-tls as esp-tls handle.

    - data -- [in] Buffer from which data will be written.

    - datalen -- [in] Length of data buffer.

  Returns:

    - >=0 if write operation was successful, the return value is the number of bytes actually written to the TLS/SSL connection.

    - <0 if write operation was not successful, because either an error occurred or an action must be taken by the calling process.

    - ESP_TLS_ERR_SSL_WANT_READ/ ESP_TLS_ERR_SSL_WANT_WRITE. if the handshake is incomplete and waiting for data to be available for reading. In this case this functions needs to be called again when the underlying transport is ready for operation.

ssize_t esp_tls_conn_read(esp_tls_t *tls, void *data, size_t datalen)

  Read from specified tls connection into the buffer 'data'.

  Parameters:

    - tls -- [in] pointer to esp-tls as esp-tls handle.

    - data -- [in] Buffer to hold read data.

    - datalen -- [in] Length of data buffer.

  Returns:

    - >0 if read operation was successful, the return value is the number of bytes actually read from the TLS/SSL connection.

    - 0 if read operation was not successful. The underlying connection was closed.

    - <0 if read operation was not successful, because either an error occurred or an action must be taken by the calling process.

int esp_tls_conn_destroy(esp_tls_t *tls)

  Close the TLS/SSL connection and free any allocated resources.

  This function should be called to close each tls connection opened with esp_tls_conn_new_sync() (or esp_tls_conn_http_new_sync()) and esp_tls_conn_new_async() (or esp_tls_conn_http_new_async()) APIs.

  Parameters:

    tls -- [in] pointer to esp-tls as esp-tls handle.

  Returns:

    - 0 on success

    - -1 if socket error or an invalid argument

ssize_t esp_tls_get_bytes_avail(esp_tls_t *tls)

  Return the number of application data bytes remaining to be read from the current record.

  This API is a wrapper over mbedtls's mbedtls_ssl_get_bytes_avail() API.

  Parameters:

    tls -- [in] pointer to esp-tls as esp-tls handle.

  Returns:

    - -1 in case of invalid arg

    - bytes available in the application data record read buffer

esp_err_t esp_tls_get_conn_sockfd(esp_tls_t *tls, int *sockfd)

  Returns the connection socket file descriptor from esp_tls session.

  Parameters:

    - tls -- [in] handle to esp_tls context

    - sockfd -- [out] int pointer to sockfd value.

  Returns:

    - ESP_OK on success and value of sockfd will be updated with socket file descriptor for connection

    - ESP_ERR_INVALID_ARG if (tls == NULL || sockfd == NULL)

esp_err_t esp_tls_set_conn_sockfd(esp_tls_t *tls, int sockfd)

  Sets the connection socket file descriptor for the esp_tls session.

  Parameters:

    - tls -- [in] handle to esp_tls context

    - sockfd -- [in] sockfd value to set.

  Returns:

    - ESP_OK on success and value of sockfd for the tls connection shall updated with the provided value

    - ESP_ERR_INVALID_ARG if (tls == NULL || sockfd < 0)

esp_err_t esp_tls_get_conn_state(esp_tls_t *tls, esp_tls_conn_state_t *conn_state)

  Gets the connection state for the esp_tls session.

  Parameters:

    - tls -- [in] handle to esp_tls context

    - conn_state -- [out] pointer to the connection state value.

  Returns:

    - ESP_OK on success and value of sockfd for the tls connection shall updated with the provided value

    - ESP_ERR_INVALID_ARG (Invalid arguments)

esp_err_t esp_tls_set_conn_state(esp_tls_t *tls, esp_tls_conn_state_t conn_state)

  Sets the connection state for the esp_tls session.

  Parameters:

    - tls -- [in] handle to esp_tls context

    - conn_state -- [in] connection state value to set.

  Returns:

    - ESP_OK on success and value of sockfd for the tls connection shall updated with the provided value

    - ESP_ERR_INVALID_ARG (Invalid arguments)

void *esp_tls_get_ssl_context(esp_tls_t *tls)

  Returns the ssl context.

  Parameters:

    tls -- [in] handle to esp_tls context

  Returns:

    - ssl_ctx pointer to ssl context of underlying TLS layer on success

    - NULL in case of error

esp_err_t esp_tls_init_global_ca_store(void)

  Create a global CA store, initially empty.

  This function should be called if the application wants to use the same CA store for multiple connections. This function initialises the global CA store which can be then set by calling esp_tls_set_global_ca_store(). To be effective, this function must be called before any call to esp_tls_set_global_ca_store().

  Returns:

    - ESP_OK if creating global CA store was successful.

    - ESP_ERR_NO_MEM if an error occurred when allocating the mbedTLS resources.

esp_err_t esp_tls_set_global_ca_store(const unsigned char *cacert_pem_buf, const unsigned int cacert_pem_bytes)

  Set the global CA store with the buffer provided in pem format.

  This function should be called if the application wants to set the global CA store for multiple connections i.e. to add the certificates in the provided buffer to the certificate chain. This function implicitly calls esp_tls_init_global_ca_store() if it has not already been called. The application must call this function before calling esp_tls_conn_new().

  Parameters:

    - cacert_pem_buf -- [in] Buffer which has certificates in pem format. This buffer is used for creating a global CA store, which can be used by other tls connections.

    - cacert_pem_bytes -- [in] Length of the buffer.

  Returns:

    - ESP_OK if adding certificates was successful.

    - Other if an error occurred or an action must be taken by the calling process.

void esp_tls_free_global_ca_store(void)

  Free the global CA store currently being used.

  The memory being used by the global CA store to store all the parsed certificates is freed up. The application can call this API if it no longer needs the global CA store.

esp_err_t esp_tls_get_and_clear_last_error(esp_tls_error_handle_t h, int *esp_tls_code, int *esp_tls_flags)

  Returns last error in esp_tls with detailed mbedtls related error codes. The error information is cleared internally upon return.

  Parameters:

    - h -- [in] esp-tls error handle.

    - esp_tls_code -- [out] last error code returned from mbedtls api (set to zero if none) This pointer could be NULL if caller does not care about esp_tls_code

    - esp_tls_flags -- [out] last certification verification flags (set to zero if none) This pointer could be NULL if caller does not care about esp_tls_code

  Returns:

    - ESP_ERR_INVALID_STATE if invalid parameters

    - ESP_OK (0) if no error occurred

    - specific error code (based on ESP_ERR_ESP_TLS_BASE) otherwise

esp_err_t esp_tls_get_and_clear_error_type(esp_tls_error_handle_t h, esp_tls_error_type_t err_type, int *error_code)

  Returns the last error captured in esp_tls of a specific type The error information is cleared internally upon return.

  Parameters:

    - h -- [in] esp-tls error handle.

    - err_type -- [in] specific error type

    - error_code -- [out] last error code returned from mbedtls api (set to zero if none) This pointer could be NULL if caller does not care about esp_tls_code

  Returns:

    - ESP_ERR_INVALID_STATE if invalid parameters

    - ESP_OK if a valid error returned and was cleared

esp_err_t esp_tls_get_error_handle(esp_tls_t *tls, esp_tls_error_handle_t *error_handle)

  Returns the ESP-TLS error_handle.

  Parameters:

    - tls -- [in] handle to esp_tls context

    - error_handle -- [out] pointer to the error handle.

  Returns:

    - ESP_OK on success and error_handle will be updated with the ESP-TLS error handle.

    - ESP_ERR_INVALID_ARG if (tls == NULL || error_handle == NULL)

mbedtls_x509_crt *esp_tls_get_global_ca_store(void)

  Get the pointer to the global CA store currently being used.

  The application must first call esp_tls_set_global_ca_store(). Then the same CA store could be used by the application for APIs other than esp_tls.

  Note

  Modifying the pointer might cause a failure in verifying the certificates.

  Returns:

    - Pointer to the global CA store currently being used if successful.

    - NULL if there is no global CA store set.

const int *esp_tls_get_ciphersuites_list(void)

  Get supported TLS ciphersuites list.

  See https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtml#tls-parameters-4 for the list of ciphersuites

  Returns:

    Pointer to a zero-terminated array of IANA identifiers of TLS ciphersuites.

esp_err_t esp_tls_server_session_init(esp_tls_cfg_server_t *cfg, int sockfd, esp_tls_t *tls)

  Initialize server side TLS/SSL connection.

  This function should be used to initialize the server side TLS/SSL connection when the application wants to handle the TLS/SSL connection asynchronously with the help of esp_tls_server_session_continue_async() function.

  Parameters:

    - cfg -- [in] Pointer to esp_tls_cfg_server_t

    - sockfd -- [in] FD of accepted connection

    - tls -- [out] Pointer to allocated esp_tls_t

  Returns:

    - ESP_OK if successful

    - ESP_ERR_INVALID_ARG if invalid arguments

    - ESP_FAIL if server session setup failed

int esp_tls_server_session_continue_async(esp_tls_t *tls)

  Asynchronous continue of esp_tls_server_session_init.

  This function should be called in a loop by the user until it returns 0. If this functions returns something other than 0, ESP_TLS_ERR_SSL_WANT_READ or ESP_TLS_ERR_SSL_WANT_WRITE, the esp-tls context must not be used and should be freed using esp_tls_conn_destroy();

  Parameters:

    tls -- [in] pointer to esp_tls_t

  Returns:

    - 0 if successful

    - <0 in case of error

    - ESP_TLS_ERR_SSL_WANT_READ/ESP_TLS_ERR_SSL_WANT_WRITE if the handshake is incomplete and waiting for data to be available for reading.

int esp_tls_server_session_create(esp_tls_cfg_server_t *cfg, int sockfd, esp_tls_t *tls)

  Create TLS/SSL server session.

  This function creates a TLS/SSL server context for already accepted client connection and performs TLS/SSL handshake with the client

  Parameters:

    - cfg -- [in] Pointer to esp_tls_cfg_server_t

    - sockfd -- [in] FD of accepted connection

    - tls -- [out] Pointer to allocated esp_tls_t

  Returns:

    - 0 if successful

    - <0 in case of error

void esp_tls_server_session_delete(esp_tls_t *tls)

  Close the server side TLS/SSL connection and free any allocated resources.

  This function should be called to close each tls connection opened with esp_tls_server_session_create()

  Parameters:

    tls -- [in] pointer to esp_tls_t

esp_err_t esp_tls_plain_tcp_connect(const char *host, int hostlen, int port, const esp_tls_cfg_t *cfg, esp_tls_error_handle_t error_handle, int *sockfd)

  Creates a plain TCP connection, returning a valid socket fd on success or an error handle.

  Parameters:

    - host -- [in] Hostname of the host.

    - hostlen -- [in] Length of hostname.

    - port -- [in] Port number of the host.

    - cfg -- [in] ESP-TLS configuration as esp_tls_cfg_t.

    - error_handle -- [out] ESP-TLS error handle holding potential errors occurred during connection

    - sockfd -- [out] Socket descriptor if successfully connected on TCP layer

  Returns:

    ESP_OK on success ESP_ERR_INVALID_ARG if invalid output parameters ESP-TLS based error codes on failure

### Structures

struct psk_key_hint

  ESP-TLS preshared key and hint structure.

  Public Members

  const uint8_t *key

    key in PSK authentication mode in binary format

  size_t key_size

    length of the key

  const char *hint

    hint in PSK authentication mode in string format

struct tls_keep_alive_cfg

  esp-tls client session ticket ctx

  Keep alive parameters structure

  Public Members

  bool keep_alive_enable

    Enable keep-alive timeout

  int keep_alive_idle

    Keep-alive idle time (second)

  int keep_alive_interval

    Keep-alive interval time (second)

  int keep_alive_count

    Keep-alive packet retry send count

struct esp_tls_cfg

  ESP-TLS configuration parameters.

  Note

  Note about format of certificates:

  - This structure includes certificates of a Certificate Authority, of client or server as well as private keys, which may be of PEM or DER format. In case of PEM format, the buffer must be NULL terminated (with NULL character included in certificate size).

  - Certificate Authority's certificate may be a chain of certificates in case of PEM format, but could be only one certificate in case of DER format

  - Variables names of certificates and private key buffers and sizes are defined as unions providing backward compatibility for legacy *_pem_buf and *_pem_bytes names which suggested only PEM format was supported. It is encouraged to use generic names such as cacert_buf and cacert_bytes.

  Public Members

  const char **alpn_protos

    Application protocols required for HTTP2. If HTTP2/ALPN support is required, a list of protocols that should be negotiated. The format is length followed by protocol name. For the most common cases the following is ok: const char **alpn_protos = { "h2", NULL };

    - where 'h2' is the protocol name

  const unsigned char *cacert_buf

    Certificate Authority's certificate in a buffer. Format may be PEM or DER, depending on mbedtls-support This buffer should be NULL terminated in case of PEM

  const unsigned char *cacert_pem_buf

    CA certificate buffer legacy name

  unsigned int cacert_bytes

    Size of Certificate Authority certificate pointed to by cacert_buf (including NULL-terminator in case of PEM format)

  unsigned int cacert_pem_bytes

    Size of Certificate Authority certificate legacy name

  const unsigned char *clientcert_buf

    Client certificate in a buffer Format may be PEM or DER, depending on mbedtls-support This buffer should be NULL terminated in case of PEM

  const unsigned char *clientcert_pem_buf

    Client certificate legacy name

  unsigned int clientcert_bytes

    Size of client certificate pointed to by clientcert_pem_buf (including NULL-terminator in case of PEM format)

  unsigned int clientcert_pem_bytes

    Size of client certificate legacy name

  const unsigned char *clientkey_buf

    Client key in a buffer Format may be PEM or DER, depending on mbedtls-support This buffer should be NULL terminated in case of PEM

  const unsigned char *clientkey_pem_buf

    Client key legacy name

  unsigned int clientkey_bytes

    Size of client key pointed to by clientkey_pem_buf (including NULL-terminator in case of PEM format)

  unsigned int clientkey_pem_bytes

    Size of client key legacy name

  const unsigned char *clientkey_password

    Client key decryption password string

  unsigned int clientkey_password_len

    String length of the password pointed to by clientkey_password

  bool use_ecdsa_peripheral

    Use the ECDSA peripheral for the private key operations

  uint8_t ecdsa_key_efuse_blk

    The efuse block where ECDSA key is stored. For SECP384R1 curve, if two blocks are used, set this to the low block and use ecdsa_key_efuse_blk_high for the high block.

  uint8_t ecdsa_key_efuse_blk_high

    The high efuse block for ECDSA key (used only for SECP384R1 curve). If not set (0), only ecdsa_key_efuse_blk is used.

  esp_tls_ecdsa_curve_t ecdsa_curve

    ECDSA curve to use (SECP256R1 or SECP384R1)

  bool non_block

    Configure non-blocking mode. If set to true the underneath socket will be configured in non blocking mode after tls session is established

  bool use_secure_element

    Enable this option to use secure element or atecc608a chip

  int timeout_ms

    Network timeout in milliseconds. Note: If this value is not set, by default the timeout is set to 10 seconds. If you wish that the session should wait indefinitely then please use a larger value e.g., INT32_MAX

  bool use_global_ca_store

    Use a global ca_store for all the connections in which this bool is set.

  const char *common_name

    If non-NULL, server certificate CN must match this name. If NULL, server certificate CN must match hostname.

  bool skip_common_name

    Skip any validation of server certificate CN field. This field should be set to false for SNI to function correctly.

  tls_keep_alive_cfg_t *keep_alive_cfg

    Enable TCP keep-alive timeout for SSL connection

  esp_err_t (*crt_bundle_attach)(void *conf)

    Function pointer to esp_crt_bundle_attach. Enables the use of certification bundle for server verification, must be enabled in menuconfig

  void *ds_data

    Pointer for digital signature peripheral context

  bool is_plain_tcp

    Use non-TLS connection: When set to true, the esp-tls uses plain TCP transport rather then TLS/SSL connection. Note, that it is possible to connect using a plain tcp transport directly with esp_tls_plain_tcp_connect() API

  struct ifreq *if_name

    The name of interface for data to go through. Use the default interface without setting

  esp_tls_addr_family_t addr_family

    The address family to use when connecting to a host.

  const int *ciphersuites_list

    Pointer to a zero-terminated array of IANA identifiers of TLS ciphersuites. Please check the list validity by esp_tls_get_ciphersuites_list() API

  esp_tls_proto_ver_t tls_version

    TLS protocol version of the connection, e.g., TLS 1.2, TLS 1.3 (default - no preference)

struct esp_tls_cfg_server

  ESP-TLS Server configuration parameters.

  Public Members

  const char **alpn_protos

    Application protocols required for HTTP2. If HTTP2/ALPN support is required, a list of protocols that should be negotiated. The format is length followed by protocol name. For the most common cases the following is ok: const char **alpn_protos = { "h2", NULL };

    - where 'h2' is the protocol name

  const unsigned char *cacert_buf

    Client CA certificate in a buffer. This buffer should be NULL terminated

  const unsigned char *cacert_pem_buf

    Client CA certificate legacy name

  unsigned int cacert_bytes

    Size of client CA certificate pointed to by cacert_pem_buf

  unsigned int cacert_pem_bytes

    Size of client CA certificate legacy name

  const unsigned char *servercert_buf

    Server certificate in a buffer This buffer should be NULL terminated

  const unsigned char *servercert_pem_buf

    Server certificate legacy name

  unsigned int servercert_bytes

    Size of server certificate pointed to by servercert_pem_buf

  unsigned int servercert_pem_bytes

    Size of server certificate legacy name

  const unsigned char *serverkey_buf

    Server key in a buffer This buffer should be NULL terminated

  const unsigned char *serverkey_pem_buf

    Server key legacy name

  unsigned int serverkey_bytes

    Size of server key pointed to by serverkey_pem_buf

  unsigned int serverkey_pem_bytes

    Size of server key legacy name

  const unsigned char *serverkey_password

    Server key decryption password string

  unsigned int serverkey_password_len

    String length of the password pointed to by serverkey_password

  bool use_ecdsa_peripheral

    Use ECDSA peripheral to use private key

  uint8_t ecdsa_key_efuse_blk

    The efuse block where ECDSA key is stored. For SECP384R1 curve, if two blocks are used, set this to the low block and use ecdsa_key_efuse_blk_high for the high block.

  uint8_t ecdsa_key_efuse_blk_high

    The high efuse block for ECDSA key (used only for SECP384R1 curve). If not set (0), only ecdsa_key_efuse_blk is used.

  esp_tls_ecdsa_curve_t ecdsa_curve

    ECDSA curve to use (SECP256R1 or SECP384R1)

  bool use_secure_element

    Enable this option to use secure element or atecc608a chip

  uint32_t tls_handshake_timeout_ms

    TLS handshake timeout in milliseconds. Note: If this value is not set, by default the timeout is set to 10 seconds. If you wish that the session should wait indefinitely then please use a larger value e.g., INT32_MAX

  void *userdata

    User data to be added to the ssl context. Can be retrieved by callbacks

  esp_tls_proto_ver_t tls_version

    TLS protocol version for this server, e.g., TLS 1.2, TLS 1.3 (default - no preference). Enables TLS version control per server instance.

  const int *ciphersuites_list

    Pointer to a zero-terminated array of IANA identifiers of TLS ciphersuites. Please check the list validity by esp_tls_get_ciphersuites_list() API. This allows per-server cipher suite configuration.

### Type Definitions

typedef enum esp_tls_conn_state esp_tls_conn_state_t

  ESP-TLS Connection State.

typedef enum esp_tls_role esp_tls_role_t

typedef struct psk_key_hint psk_hint_key_t

  ESP-TLS preshared key and hint structure.

typedef struct tls_keep_alive_cfg tls_keep_alive_cfg_t

  esp-tls client session ticket ctx

  Keep alive parameters structure

typedef enum esp_tls_addr_family esp_tls_addr_family_t

typedef struct esp_tls_cfg esp_tls_cfg_t

  ESP-TLS configuration parameters.

  Note

  Note about format of certificates:

  - This structure includes certificates of a Certificate Authority, of client or server as well as private keys, which may be of PEM or DER format. In case of PEM format, the buffer must be NULL terminated (with NULL character included in certificate size).

  - Certificate Authority's certificate may be a chain of certificates in case of PEM format, but could be only one certificate in case of DER format

  - Variables names of certificates and private key buffers and sizes are defined as unions providing backward compatibility for legacy *_pem_buf and *_pem_bytes names which suggested only PEM format was supported. It is encouraged to use generic names such as cacert_buf and cacert_bytes.

typedef void *esp_tls_handshake_callback

typedef struct esp_tls_cfg_server esp_tls_cfg_server_t

  ESP-TLS Server configuration parameters.

typedef struct esp_tls esp_tls_t

### Enumerations

enum esp_tls_conn_state

  ESP-TLS Connection State.

  Values:

  enumerator ESP_TLS_INIT
  enumerator ESP_TLS_CONNECTING
  enumerator ESP_TLS_HANDSHAKE
  enumerator ESP_TLS_FAIL
  enumerator ESP_TLS_DONE

enum esp_tls_role

  Values:

  enumerator ESP_TLS_CLIENT
  enumerator ESP_TLS_SERVER

enum esp_tls_addr_family

  Values:

  enumerator ESP_TLS_AF_UNSPEC

    Unspecified address family.

  enumerator ESP_TLS_AF_INET

    IPv4 address family.

  enumerator ESP_TLS_AF_INET6

    IPv6 address family.

enum esp_tls_proto_ver_t

  Values:

  enumerator ESP_TLS_VER_ANY
  enumerator ESP_TLS_VER_TLS_1_2
  enumerator ESP_TLS_VER_TLS_1_3
  enumerator ESP_TLS_VER_TLS_MAX

enum esp_tls_dyn_buf_strategy_t

  Values:

  enumerator ESP_TLS_DYN_BUF_RX_STATIC

    Strategy to disable dynamic RX buffer allocations and convert to static allocation post-handshake, reducing memory fragmentation

  enumerator ESP_TLS_DYN_BUF_STRATEGY_MAX

    to indicate max

enum esp_tls_ecdsa_curve_t

  ECDSA curve options for TLS connections.

  Values:

  enumerator ESP_TLS_ECDSA_CURVE_SECP256R1

    Use SECP256R1 curve

  enumerator ESP_TLS_ECDSA_CURVE_MAX

    to indicate max

### Header File

- components/esp-tls/esp_tls_errors.h

- This header file can be included with:

  >     #include "esp_tls_errors.h"

- This header file is a part of the API provided by the `esp-tls` component. To declare that your component depends on `esp-tls`, add the following to your CMakeLists.txt:

  >     REQUIRES esp-tls

  > or

  >     PRIV_REQUIRES esp-tls

### Structures

struct esp_tls_last_error

  Error structure containing relevant errors in case tls error occurred.

  Public Members

  esp_err_t last_error

    error code (based on ESP_ERR_ESP_TLS_BASE) of the last occurred error

  int esp_tls_error_code

    esp_tls error code from last esp_tls failed api

  int esp_tls_flags

    last certification verification flags

### Macros

ESP_ERR_ESP_TLS_BASE

  Starting number of ESP-TLS error codes

ESP_ERR_ESP_TLS_CANNOT_RESOLVE_HOSTNAME

  Error if hostname couldn't be resolved upon tls connection

ESP_ERR_ESP_TLS_CANNOT_CREATE_SOCKET

  Failed to create socket

ESP_ERR_ESP_TLS_UNSUPPORTED_PROTOCOL_FAMILY

  Unsupported protocol family

ESP_ERR_ESP_TLS_FAILED_CONNECT_TO_HOST

  Failed to connect to host

ESP_ERR_ESP_TLS_SOCKET_SETOPT_FAILED

  failed to set/get socket option

ESP_ERR_ESP_TLS_CONNECTION_TIMEOUT

  new connection in esp_tls_low_level_conn connection timeouted

ESP_ERR_ESP_TLS_SE_FAILED

ESP_ERR_ESP_TLS_TCP_CLOSED_FIN

ESP_ERR_ESP_TLS_SERVER_HANDSHAKE_TIMEOUT

  TLS handshake timeout

ESP_ERR_MBEDTLS_CERT_PARTLY_OK

  mbedtls parse certificates was partly successful

ESP_ERR_MBEDTLS_CTR_DRBG_SEED_FAILED

  mbedtls api returned error

ESP_ERR_MBEDTLS_SSL_SET_HOSTNAME_FAILED

  mbedtls api returned error

ESP_ERR_MBEDTLS_SSL_CONFIG_DEFAULTS_FAILED

  mbedtls api returned error

ESP_ERR_MBEDTLS_SSL_CONF_ALPN_PROTOCOLS_FAILED

  mbedtls api returned error

ESP_ERR_MBEDTLS_X509_CRT_PARSE_FAILED

  mbedtls api returned error

ESP_ERR_MBEDTLS_SSL_CONF_OWN_CERT_FAILED

  mbedtls api returned error

ESP_ERR_MBEDTLS_SSL_SETUP_FAILED

  mbedtls api returned error

ESP_ERR_MBEDTLS_SSL_WRITE_FAILED

  mbedtls api returned error

ESP_ERR_MBEDTLS_PK_PARSE_KEY_FAILED

  mbedtls api returned failed

ESP_ERR_MBEDTLS_SSL_HANDSHAKE_FAILED

  mbedtls api returned failed

ESP_ERR_MBEDTLS_SSL_CONF_PSK_FAILED

  mbedtls api returned failed

ESP_ERR_MBEDTLS_SSL_TICKET_SETUP_FAILED

  mbedtls api returned failed

ESP_ERR_MBEDTLS_SSL_READ_FAILED

  mbedtls api returned failed

ESP_ERR_WOLFSSL_SSL_SET_HOSTNAME_FAILED

  wolfSSL api returned error

ESP_ERR_WOLFSSL_SSL_CONF_ALPN_PROTOCOLS_FAILED

  wolfSSL api returned error

ESP_ERR_WOLFSSL_CERT_VERIFY_SETUP_FAILED

  wolfSSL api returned error

ESP_ERR_WOLFSSL_KEY_VERIFY_SETUP_FAILED

  wolfSSL api returned error

ESP_ERR_WOLFSSL_SSL_HANDSHAKE_FAILED

  wolfSSL api returned failed

ESP_ERR_WOLFSSL_CTX_SETUP_FAILED

  wolfSSL api returned failed

ESP_ERR_WOLFSSL_SSL_SETUP_FAILED

  wolfSSL api returned failed

ESP_ERR_WOLFSSL_SSL_WRITE_FAILED

  wolfSSL api returned failed

ESP_TLS_ERR_SSL_WANT_READ

  Definition of errors reported from IO API (potentially non-blocking) in case of error:

  - esp_tls_conn_read()

  - esp_tls_conn_write()

ESP_TLS_ERR_SSL_WANT_WRITE

ESP_TLS_ERR_SSL_TIMEOUT

### Type Definitions

typedef struct esp_tls_last_error *esp_tls_error_handle_t

typedef struct esp_tls_last_error esp_tls_last_error_t

  Error structure containing relevant errors in case tls error occurred.

### Enumerations

enum esp_tls_error_type_t

  Definition of different types/sources of error codes reported from different components

  Values:

  enumerator ESP_TLS_ERR_TYPE_UNKNOWN
  enumerator ESP_TLS_ERR_TYPE_SYSTEM

    System error – errno

  enumerator ESP_TLS_ERR_TYPE_MBEDTLS

    Error code from mbedTLS library

  enumerator ESP_TLS_ERR_TYPE_MBEDTLS_CERT_FLAGS

    Certificate flags defined in mbedTLS

  enumerator ESP_TLS_ERR_TYPE_ESP

    ESP-IDF error type – esp_err_t

  enumerator ESP_TLS_ERR_TYPE_WOLFSSL

    Error code from wolfSSL library

  enumerator ESP_TLS_ERR_TYPE_WOLFSSL_CERT_FLAGS

    Certificate flags defined in wolfSSL

  enumerator ESP_TLS_ERR_TYPE_MAX

    Last err type – invalid entry

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