Protocol Communication

Overview

Protocol Communication (protocomm) component manages secure sessions and provides framework for multiple transports. The application can also use protocomm layer directly to have application specific extensions for the provisioning (or non-provisioning) use cases.

Following features are available for provisioning :
  • Communication security at application level -

    • protocomm_security0 (no security)

    • protocomm_security1 (Curve25519 key exchange + AES-CTR encryption/decryption)

    • protocomm_security2 (SRP6a-based key exchange + AES-GCM encryption/decryption)

  • Proof-of-possession (support with protocomm_security1 only)

  • Salt and Verifier (support with protocomm_security2 only)

Protocomm internally uses protobuf (protocol buffers) for secure session establishment. Though users can implement their own security (even without using protobuf). One can even use protocomm without any security layer.

Protocomm provides framework for various transports :

  • BLE

  • console, in which case the handler invocation is automatically taken care of on the device side (see Transport Examples below for code snippets).

Note that the client still needs to establish session (for protocomm_security1 and protocomm_security2) by performing the two way handshake. See Unified Provisioning for more details about the secure handshake logic.

Enabling protocomm security version

Protocomm component provides project configuration menu to enable/disable support of respective security versions. The respective configuration options can be found as follows:

Note

Enabling multiple security versions allow to control them dynamically but also increases firmware size.

Transport Example (BLE) with Security 0

For sample usage, see wifi_provisioning/src/scheme_ble.c

/* Example function for launching a secure protocomm instance over BLE */
protocomm_t *start_pc()
{
    protocomm_t *pc = protocomm_new();

    /* Endpoint UUIDs */
    protocomm_ble_name_uuid_t nu_lookup_table[] = {
        {"security_endpoint", 0xFF51},
        {"echo_req_endpoint", 0xFF52}
    };

    /* Config for protocomm_ble_start() */
    protocomm_ble_config_t config = {
        .service_uuid = {
            /* LSB <---------------------------------------
            * ---------------------------------------> MSB */
            0xfb, 0x34, 0x9b, 0x5f, 0x80, 0x00, 0x00, 0x80,
            0x00, 0x10, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00,
        },
        .nu_lookup_count = sizeof(nu_lookup_table)/sizeof(nu_lookup_table[0]),
        .nu_lookup = nu_lookup_table
    };

    /* Start protocomm layer on top of BLE */
    protocomm_ble_start(pc, &config);

    /* For protocomm_security0, Proof of Possession is not used, and can be kept NULL */
    protocomm_set_security(pc, "security_endpoint", &protocomm_security0, NULL);
    protocomm_add_endpoint(pc, "echo_req_endpoint", echo_req_handler, NULL);
    return pc;
}

/* Example function for stopping a protocomm instance */
void stop_pc(protocomm_t *pc)
{
    protocomm_remove_endpoint(pc, "echo_req_endpoint");
    protocomm_unset_security(pc, "security_endpoint");

    /* Stop BLE protocomm service */
    protocomm_ble_stop(pc);

    protocomm_delete(pc);
}

API Reference

Header File

Functions

protocomm_t *protocomm_new(void)

Create a new protocomm instance.

This API will return a new dynamically allocated protocomm instance with all elements of the protocomm_t structure initialized to NULL.

Returns

  • protocomm_t* : On success

  • NULL : No memory for allocating new instance

void protocomm_delete(protocomm_t *pc)

Delete a protocomm instance.

This API will deallocate a protocomm instance that was created using protocomm_new().

Parameters

pc – [in] Pointer to the protocomm instance to be deleted

esp_err_t protocomm_add_endpoint(protocomm_t *pc, const char *ep_name, protocomm_req_handler_t h, void *priv_data)

Add endpoint request handler for a protocomm instance.

This API will bind an endpoint handler function to the specified endpoint name, along with any private data that needs to be pass to the handler at the time of call.

Note

  • An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

  • This function internally calls the registered add_endpoint() function of the selected transport which is a member of the protocomm_t instance structure.

Parameters

  • pc – [in] Pointer to the protocomm instance

  • ep_name – [in] Endpoint identifier(name) string

  • h – [in] Endpoint handler function

  • priv_data – [in] Pointer to private data to be passed as a parameter to the handler function on call. Pass NULL if not needed.

Returns

  • ESP_OK : Success

  • ESP_FAIL : Error adding endpoint / Endpoint with this name already exists

  • ESP_ERR_NO_MEM : Error allocating endpoint resource

  • ESP_ERR_INVALID_ARG : Null instance/name/handler arguments

esp_err_t protocomm_remove_endpoint(protocomm_t *pc, const char *ep_name)

Remove endpoint request handler for a protocomm instance.

This API will remove a registered endpoint handler identified by an endpoint name.

Note

  • This function internally calls the registered remove_endpoint() function which is a member of the protocomm_t instance structure.

Parameters

  • pc – [in] Pointer to the protocomm instance

  • ep_name – [in] Endpoint identifier(name) string

Returns

  • ESP_OK : Success

  • ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist

  • ESP_ERR_INVALID_ARG : Null instance/name arguments

esp_err_t protocomm_open_session(protocomm_t *pc, uint32_t session_id)

Allocates internal resources for new transport session.

Note

  • An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

Parameters

  • pc – [in] Pointer to the protocomm instance

  • session_id – [in] Unique ID for a communication session

Returns

  • ESP_OK : Request handled successfully

  • ESP_ERR_NO_MEM : Error allocating internal resource

  • ESP_ERR_INVALID_ARG : Null instance/name arguments

esp_err_t protocomm_close_session(protocomm_t *pc, uint32_t session_id)

Frees internal resources used by a transport session.

Note

  • An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

Parameters

  • pc – [in] Pointer to the protocomm instance

  • session_id – [in] Unique ID for a communication session

Returns

  • ESP_OK : Request handled successfully

  • ESP_ERR_INVALID_ARG : Null instance/name arguments

esp_err_t protocomm_req_handle(protocomm_t *pc, const char *ep_name, uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t **outbuf, ssize_t *outlen)

Calls the registered handler of an endpoint session for processing incoming data and generating the response.

Note

  • An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

  • Resulting output buffer must be deallocated by the caller.

Parameters

  • pc – [in] Pointer to the protocomm instance

  • ep_name – [in] Endpoint identifier(name) string

  • session_id – [in] Unique ID for a communication session

  • inbuf – [in] Input buffer contains input request data which is to be processed by the registered handler

  • inlen – [in] Length of the input buffer

  • outbuf – [out] Pointer to internally allocated output buffer, where the resulting response data output from the registered handler is to be stored

  • outlen – [out] Buffer length of the allocated output buffer

Returns

  • ESP_OK : Request handled successfully

  • ESP_FAIL : Internal error in execution of registered handler

  • ESP_ERR_NO_MEM : Error allocating internal resource

  • ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist

  • ESP_ERR_INVALID_ARG : Null instance/name arguments

esp_err_t protocomm_set_security(protocomm_t *pc, const char *ep_name, const protocomm_security_t *sec, const void *sec_params)

Add endpoint security for a protocomm instance.

This API will bind a security session establisher to the specified endpoint name, along with any proof of possession that may be required for authenticating a session client.

Note

  • An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

  • The choice of security can be any protocomm_security_t instance. Choices protocomm_security0 and protocomm_security1 and protocomm_security2 are readily available.

Parameters

  • pc – [in] Pointer to the protocomm instance

  • ep_name – [in] Endpoint identifier(name) string

  • sec – [in] Pointer to endpoint security instance

  • sec_params – [in] Pointer to security params (NULL if not needed) The pointer should contain the security params struct of appropriate security version. For protocomm security version 1 and 2 sec_params should contain pointer to struct of type protocomm_security1_params_t and protocmm_security2_params_t respectively. The contents of this pointer must be valid till the security session has been running and is not closed.

Returns

  • ESP_OK : Success

  • ESP_FAIL : Error adding endpoint / Endpoint with this name already exists

  • ESP_ERR_INVALID_STATE : Security endpoint already set

  • ESP_ERR_NO_MEM : Error allocating endpoint resource

  • ESP_ERR_INVALID_ARG : Null instance/name/handler arguments

esp_err_t protocomm_unset_security(protocomm_t *pc, const char *ep_name)

Remove endpoint security for a protocomm instance.

This API will remove a registered security endpoint identified by an endpoint name.

Parameters

  • pc – [in] Pointer to the protocomm instance

  • ep_name – [in] Endpoint identifier(name) string

Returns

  • ESP_OK : Success

  • ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist

  • ESP_ERR_INVALID_ARG : Null instance/name arguments

esp_err_t protocomm_set_version(protocomm_t *pc, const char *ep_name, const char *version)

Set endpoint for version verification.

This API can be used for setting an application specific protocol version which can be verified by clients through the endpoint.

Note

  • An endpoint must be bound to a valid protocomm instance, created using protocomm_new().

Parameters

  • pc – [in] Pointer to the protocomm instance

  • ep_name – [in] Endpoint identifier(name) string

  • version – [in] Version identifier(name) string

Returns

  • ESP_OK : Success

  • ESP_FAIL : Error adding endpoint / Endpoint with this name already exists

  • ESP_ERR_INVALID_STATE : Version endpoint already set

  • ESP_ERR_NO_MEM : Error allocating endpoint resource

  • ESP_ERR_INVALID_ARG : Null instance/name/handler arguments

esp_err_t protocomm_unset_version(protocomm_t *pc, const char *ep_name)

Remove version verification endpoint from a protocomm instance.

This API will remove a registered version endpoint identified by an endpoint name.

Parameters

  • pc – [in] Pointer to the protocomm instance

  • ep_name – [in] Endpoint identifier(name) string

Returns

  • ESP_OK : Success

  • ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist

  • ESP_ERR_INVALID_ARG : Null instance/name arguments

Type Definitions

typedef esp_err_t (*protocomm_req_handler_t)(uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t **outbuf, ssize_t *outlen, void *priv_data)

Function prototype for protocomm endpoint handler.

typedef struct protocomm protocomm_t

This structure corresponds to a unique instance of protocomm returned when the API protocomm_new() is called. The remaining Protocomm APIs require this object as the first parameter.

Note

Structure of the protocomm object is kept private

Header File

Structures

struct protocomm_security1_params

Protocomm Security 1 parameters: Proof Of Possession.

Public Members

const uint8_t *data

Pointer to buffer containing the proof of possession data

uint16_t len

Length (in bytes) of the proof of possession data

struct protocomm_security2_params

Protocomm Security 2 parameters: Salt and Verifier.

Public Members

const char *salt

Pointer to the buffer containing the salt

uint16_t salt_len

Length (in bytes) of the salt

const char *verifier

Pointer to the buffer containing the verifier

uint16_t verifier_len

Length (in bytes) of the verifier

struct protocomm_security

Protocomm security object structure.

The member functions are used for implementing secure protocomm sessions.

Note

This structure should not have any dynamic members to allow re-entrancy

Public Members

int ver

Unique version number of security implementation

esp_err_t (*init)(protocomm_security_handle_t *handle)

Function for initializing/allocating security infrastructure

esp_err_t (*cleanup)(protocomm_security_handle_t handle)

Function for deallocating security infrastructure

esp_err_t (*new_transport_session)(protocomm_security_handle_t handle, uint32_t session_id)

Starts new secure transport session with specified ID

esp_err_t (*close_transport_session)(protocomm_security_handle_t handle, uint32_t session_id)

Closes a secure transport session with specified ID

esp_err_t (*security_req_handler)(protocomm_security_handle_t handle, const void *sec_params, uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t **outbuf, ssize_t *outlen, void *priv_data)

Handler function for authenticating connection request and establishing secure session

esp_err_t (*encrypt)(protocomm_security_handle_t handle, uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t **outbuf, ssize_t *outlen)

Function which implements the encryption algorithm

esp_err_t (*decrypt)(protocomm_security_handle_t handle, uint32_t session_id, const uint8_t *inbuf, ssize_t inlen, uint8_t **outbuf, ssize_t *outlen)

Function which implements the decryption algorithm

Type Definitions

typedef struct protocomm_security1_params protocomm_security1_params_t

Protocomm Security 1 parameters: Proof Of Possession.

typedef protocomm_security1_params_t protocomm_security_pop_t
typedef struct protocomm_security2_params protocomm_security2_params_t

Protocomm Security 2 parameters: Salt and Verifier.

typedef void *protocomm_security_handle_t
typedef struct protocomm_security protocomm_security_t

Protocomm security object structure.

The member functions are used for implementing secure protocomm sessions.

Note

This structure should not have any dynamic members to allow re-entrancy

Header File

Header File

Header File

Functions

esp_err_t protocomm_httpd_start(protocomm_t *pc, const protocomm_httpd_config_t *config)

Start HTTPD protocomm transport.

This API internally creates a framework to allow endpoint registration and security configuration for the protocomm.

Note

This is a singleton. ie. Protocomm can have multiple instances, but only one instance can be bound to an HTTP transport layer.

Parameters

  • pc – [in] Protocomm instance pointer obtained from protocomm_new()

  • config – [in] Pointer to config structure for initializing HTTP server

Returns

  • ESP_OK : Success

  • ESP_ERR_INVALID_ARG : Null arguments

  • ESP_ERR_NOT_SUPPORTED : Transport layer bound to another protocomm instance

  • ESP_ERR_INVALID_STATE : Transport layer already bound to this protocomm instance

  • ESP_ERR_NO_MEM : Memory allocation for server resource failed

  • ESP_ERR_HTTPD_* : HTTP server error on start

esp_err_t protocomm_httpd_stop(protocomm_t *pc)

Stop HTTPD protocomm transport.

This API cleans up the HTTPD transport protocomm and frees all the handlers registered with the protocomm.

Parameters

pc – [in] Same protocomm instance that was passed to protocomm_httpd_start()

Returns

  • ESP_OK : Success

  • ESP_ERR_INVALID_ARG : Null / incorrect protocomm instance pointer

Unions

union protocomm_httpd_config_data_t
#include <protocomm_httpd.h>

Protocomm HTTPD Configuration Data

Public Members

void *handle

HTTP Server Handle, if ext_handle_provided is set to true

protocomm_http_server_config_t config

HTTP Server Configuration, if a server is not already active

Structures

struct protocomm_http_server_config_t

Config parameters for protocomm HTTP server.

Public Members

uint16_t port

Port on which the HTTP server will listen

size_t stack_size

Stack size of server task, adjusted depending upon stack usage of endpoint handler

unsigned task_priority

Priority of server task

struct protocomm_httpd_config_t

Config parameters for protocomm HTTP server.

Public Members

bool ext_handle_provided

Flag to indicate of an external HTTP Server Handle has been provided. In such as case, protocomm will use the same HTTP Server and not start a new one internally.

protocomm_httpd_config_data_t data

Protocomm HTTPD Configuration Data

Macros

PROTOCOMM_HTTPD_DEFAULT_CONFIG()

Header File

Functions

esp_err_t protocomm_ble_start(protocomm_t *pc, const protocomm_ble_config_t *config)

Start Bluetooth Low Energy based transport layer for provisioning.

Initialize and start required BLE service for provisioning. This includes the initialization for characteristics/service for BLE.

Parameters

  • pc – [in] Protocomm instance pointer obtained from protocomm_new()

  • config – [in] Pointer to config structure for initializing BLE

Returns

  • ESP_OK : Success

  • ESP_FAIL : Simple BLE start error

  • ESP_ERR_NO_MEM : Error allocating memory for internal resources

  • ESP_ERR_INVALID_STATE : Error in ble config

  • ESP_ERR_INVALID_ARG : Null arguments

esp_err_t protocomm_ble_stop(protocomm_t *pc)

Stop Bluetooth Low Energy based transport layer for provisioning.

Stops service/task responsible for BLE based interactions for provisioning

Note

You might want to optionally reclaim memory from Bluetooth. Refer to the documentation of esp_bt_mem_release in that case.

Parameters

pc – [in] Same protocomm instance that was passed to protocomm_ble_start()

Returns

  • ESP_OK : Success

  • ESP_FAIL : Simple BLE stop error

  • ESP_ERR_INVALID_ARG : Null / incorrect protocomm instance

Structures

struct name_uuid

This structure maps handler required by protocomm layer to UUIDs which are used to uniquely identify BLE characteristics from a smartphone or a similar client device.

Public Members

const char *name

Name of the handler, which is passed to protocomm layer

uint16_t uuid

UUID to be assigned to the BLE characteristic which is mapped to the handler

struct protocomm_ble_config

Config parameters for protocomm BLE service.

Public Members

char device_name[MAX_BLE_DEVNAME_LEN + 1]

BLE device name being broadcast at the time of provisioning

uint8_t service_uuid[BLE_UUID128_VAL_LENGTH]

128 bit UUID of the provisioning service

uint8_t *manufacturer_data

BLE device manufacturer data pointer in advertisement

ssize_t manufacturer_data_len

BLE device manufacturer data length in advertisement

ssize_t nu_lookup_count

Number of entries in the Name-UUID lookup table

protocomm_ble_name_uuid_t *nu_lookup

Pointer to the Name-UUID lookup table

unsigned ble_bonding

BLE bonding

unsigned ble_sm_sc

BLE security flag

unsigned ble_link_encryption

BLE security flag

Macros

MAX_BLE_DEVNAME_LEN

BLE device name cannot be larger than this value 31 bytes (max scan response size) - 1 byte (length) - 1 byte (type) = 29 bytes

BLE_UUID128_VAL_LENGTH
MAX_BLE_MANUFACTURER_DATA_LEN

Theoretically, the limit for max manufacturer length remains same as BLE device name i.e. 31 bytes (max scan response size) - 1 byte (length) - 1 byte (type) = 29 bytes However, manufacturer data goes along with BLE device name in scan response. So, it is important to understand the actual length should be smaller than (29 - (BLE device name length) - 2).

Type Definitions

typedef struct name_uuid protocomm_ble_name_uuid_t

This structure maps handler required by protocomm layer to UUIDs which are used to uniquely identify BLE characteristics from a smartphone or a similar client device.

typedef struct protocomm_ble_config protocomm_ble_config_t

Config parameters for protocomm BLE service.

Enumerations

enum protocomm_transport_ble_event_t

Events generated by BLE transport.

These events are generated when the BLE transport is paired and disconnected.

Values:

enumerator PROTOCOMM_TRANSPORT_BLE_CONNECTED
enumerator PROTOCOMM_TRANSPORT_BLE_DISCONNECTED

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