ESP-TLS¶
Overview¶
The ESP-TLS component provides a simplified API interface for accessing the commonly used TLS functionality.
It supports common scenarios like CA certification validation, SNI, ALPN negotiation, non-blocking connection among others.
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:
esp_tls_conn_new()
: for opening a new TLS connection.esp_tls_conn_read()
: for reading from the connection.esp_tls_conn_write()
: for writing into the connection.esp_tls_conn_delete()
: 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 contain the public API headers for the component. Internally ESP-TLS component uses one of the two SSL/TLS Libraries between mbedtls and wolfssl for its operation. API specific to mbedtls are present in esp-tls/private_include/esp_tls_mbedtls.h and API specific to wolfssl are present in esp-tls/private_include/esp_tls_wolfssl.h.
Underlying SSL/TLS Library Options¶
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 used, wolfssl SSL/TLS library is available publicly at https://github.com/espressif/esp-wolfssl. The repository provides wolfssl component in binary format, it also provides few examples which are useful for understanding the API. Please refer the repository README.md for information on licensing and other options. Please see below option for using wolfssl in your project.
注解
As the library options are internal to ESP-TLS, switching the libries 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
Directly add wolfssl as a component in your project with following three commands.:
(First change directory (cd) to your project directory) mkdir components cd components git clone https://github.com/espressif/esp-wolfssl.git
Add wolfssl as an extra component in your project.
Download wolfssl with:
git clone https://github.com/espressif/esp-wolfssl.git
Include esp-wolfssl in ESP-IDF with setting EXTRA_COMPONENT_DIRS in CMakeLists.txt/Makefile of your project as done in wolfssl/examples. For reference see Optional Project variables in build-system.
After above steps, you will have option to choose wolfssl as underlying SSL/TLS library in configuration menu of your project as follows:
idf.py/make menuconfig -> ESP-TLS -> choose SSL/TLS Library -> mbedtls/wolfssl
Comparison between mbedtls and wolfssl¶
The following table shows a typical comparison between wolfssl and mbedtls when protocols/https_request example (which has server authentication) was run with both SSL/TLS libraries and with all respective configurations set to default. (mbedtls IN_CONTENT length and OUT_CONTENT length were 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
注解
These values are subject to change with change in configuration options and version of respective libraries.
API Reference¶
Header File¶
Functions¶
-
esp_tls_t *
esp_tls_init
(void)¶ Create TLS connection.
This function allocates and initializes esp-tls structure handle.
- Return
- tls Pointer to esp-tls as esp-tls handle if successfully initialized, NULL if allocation error
-
esp_tls_t *
esp_tls_conn_new
(const char *hostname, int hostlen, int port, const esp_tls_cfg_t *cfg)¶ Create a new blocking TLS/SSL connection.
This function establishes a TLS/SSL connection with the specified host in blocking manner.
Note: This API is present for backward compatibility reasons. Alternative function with the same functionality is
esp_tls_conn_new_sync
(and its asynchronous versionesp_tls_conn_new_async
)- Return
- pointer to esp_tls_t, or NULL if connection couldn’t be opened.
- Parameters
hostname
: Hostname of the host.hostlen
: Length of hostname.port
: Port number of the host.cfg
: 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.
-
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.
- Return
- -1 If connection establishment fails.
- 1 If connection establishment is successful.
- 0 If connection state is in progress.
- Parameters
hostname
: Hostname of the host.hostlen
: Length of hostname.port
: Port number of the host.cfg
: 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
: Pointer to esp-tls as esp-tls handle.
-
esp_tls_t *
esp_tls_conn_http_new
(const char *url, const esp_tls_cfg_t *cfg)¶ Create a new blocking TLS/SSL connection with a given “HTTP” url.
The behaviour is same as esp_tls_conn_new() API. However this API accepts host’s url.
- Return
- pointer to esp_tls_t, or NULL if connection couldn’t be opened.
- Parameters
url
: url of host.cfg
: 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.
-
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.
- Return
- -1 If connection establishment fails.
- 0 If connection establishment is in progress.
- 1 If connection establishment is successful.
- Parameters
hostname
: Hostname of the host.hostlen
: Length of hostname.port
: Port number of the host.cfg
: TLS configuration as esp_tls_cfg_t.non_block
member of this structure should be set to be true.tls
: pointer to esp-tls as esp-tls handle.
-
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() API. However this API accepts host’s url.
- Return
- -1 If connection establishment fails.
- 0 If connection establishment is in progress.
- 1 If connection establishment is successful.
- Parameters
url
: url of host.cfg
: TLS configuration as esp_tls_cfg_t.tls
: pointer to esp-tls as esp-tls handle.
-
static ssize_t
esp_tls_conn_write
(esp_tls_t *tls, const void *data, size_t datalen)¶ Write from buffer ‘data’ into specified tls connection.
- Return
- >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. The underlying connection was closed.
- <0 if write operation was not successful, because either an error occured or an action must be taken by the calling process.
- Parameters
tls
: pointer to esp-tls as esp-tls handle.data
: Buffer from which data will be written.datalen
: Length of data buffer.
-
static ssize_t
esp_tls_conn_read
(esp_tls_t *tls, void *data, size_t datalen)¶ Read from specified tls connection into the buffer ‘data’.
- Return
- >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 occured or an action must be taken by the calling process.
- Parameters
tls
: pointer to esp-tls as esp-tls handle.data
: Buffer to hold read data.datalen
: Length of data buffer.
-
void
esp_tls_conn_delete
(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() or esp_tls_conn_http_new() APIs.
- Parameters
tls
: pointer to esp-tls as esp-tls handle.
-
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.
- Return
- -1 in case of invalid arg
- bytes available in the application data record read buffer
- Parameters
tls
: pointer to esp-tls as esp-tls handle.
-
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().
- Return
- ESP_OK if creating global CA store was successful.
- ESP_ERR_NO_MEM if an error occured 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().
- Return
- ESP_OK if adding certificates was successful.
- Other if an error occured or an action must be taken by the calling process.
- Parameters
cacert_pem_buf
: 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
: Length of the buffer.
-
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.
- Return
- 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
- Parameters
h
: esp-tls error handle.esp_tls_code
: 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_codeesp_tls_flags
: last certification verification flags (set to zero if none) This pointer could be NULL if caller does not care about esp_tls_code
Structures¶
-
struct
esp_tls_last_error
¶ Error structure containing relevant errors in case tls error occurred.
-
struct
psk_key_hint
¶ ESP-TLS preshared key and hint structure.
-
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
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
-
int
timeout_ms
¶ Network timeout in milliseconds
-
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
-
const psk_hint_key_t *
psk_hint_key
¶ Pointer to PSK hint and key. if not NULL (and certificates are NULL) then PSK authentication is enabled with configured setup. Important note: the pointer must be valid for connection
-
struct
esp_tls
¶ ESP-TLS Connection Handle.
Public Members
-
int
sockfd
¶ Underlying socket file descriptor.
-
ssize_t (*
read
)(struct esp_tls *tls, char *data, size_t datalen)¶ Callback function for reading data from TLS/SSL connection.
-
ssize_t (*
write
)(struct esp_tls *tls, const char *data, size_t datalen)¶ Callback function for writing data to TLS/SSL connection.
-
esp_tls_conn_state_t
conn_state
¶ ESP-TLS Connection state
-
fd_set
rset
¶ read file descriptors
-
fd_set
wset
¶ write file descriptors
-
bool
is_tls
¶ indicates connection type (TLS or NON-TLS)
-
esp_tls_role_t
role
¶ esp-tls role
- ESP_TLS_CLIENT
- ESP_TLS_SERVER
-
esp_tls_error_handle_t
error_handle
¶ handle to error descriptor
-
int
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 socket option
-
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_ESP_TLS_CONNECTION_TIMEOUT
¶ new connection in esp_tls_low_level_conn connection timeouted
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.
-
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 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.