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)
  • Proof-of-possession (support with protocomm_security1 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 - WiFi (SoftAP+HTTPD), 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 (only for protocomm_security1) by performing the two way handshake. See Unified Provisioning for more details about the secure handshake logic.

Transport Example (SoftAP + HTTP) with Security 1

For complete example see provisioning/softap_prov

/* Endpoint handler to be registered with protocomm.
 * This simply echoes back the received data. */
esp_err_t echo_req_handler (uint32_t session_id,
                            const uint8_t *inbuf, ssize_t inlen,
                            uint8_t **outbuf, ssize_t *outlen,
                            void *priv_data)
{
    /* Session ID may be used for persistence */
    printf("Session ID : %d", session_id);

    /* Echo back the received data */
    *outlen = inlen;            /* Output data length updated */
    *outbuf = malloc(inlen);    /* This will be deallocated outside */
    memcpy(*outbuf, inbuf, inlen);

    /* Private data that was passed at the time of endpoint creation */
    uint32_t *priv = (uint32_t *) priv_data;
    if (priv) {
        printf("Private data : %d", *priv);
    }

    return ESP_OK;
}

/* Example function for launching a protocomm instance over HTTP */
protocomm_t *start_pc(const char *pop_string)
{
    protocomm_t *pc = protocomm_new();

    /* Config for protocomm_httpd_start() */
    protocomm_httpd_config_t pc_config = PROTOCOMM_HTTPD_DEFAULT_CONFIG();

    /* Start protocomm server on top of HTTP */
    protocomm_httpd_start(pc, &pc_config);

    /* Create Proof of Possession object from pop_string. It must be valid
     * throughout the scope of protocomm endpoint. This need not be static,
     * ie. could be dynamically allocated and freed at the time of endpoint
     * removal */
    const static protocomm_security_pop_t pop_obj = {
        .data = (const uint8_t *) strdup(pop_string),
        .len = strlen(pop_string)
    };

    /* Set security for communication at application level. Just like for
     * request handlers, setting security creates an endpoint and registers
     * the handler provided by protocomm_security1. One can similarly use
     * protocomm_security0. Only one type of security can be set for a
     * protocomm instance at a time. */
    protocomm_set_security(pc, "security_endpoint", &protocomm_security1, &pop_obj);

    /* Private data passed to the endpoint must be valid throughout the scope
     * of protocomm endpoint. This need not be static, ie. could be dynamically
     * allocated and freed at the time of endpoint removal */
    static uint32_t priv_data = 1234;

    /* Add a new endpoint for the protocomm instance, identified by a unique name
     * and register a handler function along with private data to be passed at the
     * time of handler execution. Multiple endpoints can be added as long as they
     * are identified by unique names */
    protocomm_add_endpoint(pc, "echo_req_endpoint",
                           echo_req_handler, (void *) &priv_data);
    return pc;
}

/* Example function for stopping a protocomm instance */
void stop_pc(protocomm_t *pc)
{
    /* Remove endpoint identified by it's unique name */
    protocomm_remove_endpoint(pc, "echo_req_endpoint");

    /* Remove security endpoint identified by it's name */
    protocomm_unset_security(pc, "security_endpoint");

    /* Stop HTTP server */
    protocomm_httpd_stop(pc);

    /* Delete (deallocate) the protocomm instance */
    protocomm_delete(pc);
}

Transport Example (BLE) with Security 0

For complete example see provisioning/ble_prov

/* 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

Functions

protocomm_t *protocomm_new()

Create a new protocomm instance.

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

Return
  • 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: 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 which is a member of the protocomm_t instance structure.
Return
  • ESP_OK : Added new endpoint succesfully
  • 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
Parameters
  • pc: Pointer to the protocomm instance
  • ep_name: Endpoint identifier(name) string
  • h: Endpoint handler function
  • priv_data: Pointer to private data to be passed as a parameter to the handler function on call. Pass NULL if not needed.

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.
Return
  • ESP_OK : Added new endpoint succesfully
  • ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist
  • ESP_ERR_INVALID_ARG : Null instance/name arguments
Parameters
  • pc: Pointer to the protocomm instance
  • ep_name: Endpoint identifier(name) string

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 giving the output.

Note
  • An endpoint must be bound to a valid protocomm instance, created using protocomm_new().
  • Resulting output buffer must be deallocated by the user.
Return
  • ESP_OK : Request handled succesfully
  • 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
Parameters
  • pc: Pointer to the protocomm instance
  • ep_name: Endpoint identifier(name) string
  • session_id: Unique ID for a communication session
  • inbuf: Input buffer contains input request data which is to be processed by the registered handler
  • inlen: Length of the input buffer
  • outbuf: Pointer to internally allocated output buffer, where the resulting response data output from the registered handler is to be stored
  • outlen: Buffer length of the allocated output buffer

esp_err_t protocomm_set_security(protocomm_t *pc, const char *ep_name, const protocomm_security_t *sec, const protocomm_security_pop_t *pop)

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 are readily available.
Return
  • ESP_OK : Added new security endpoint succesfully
  • 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
Parameters
  • pc: Pointer to the protocomm instance
  • ep_name: Endpoint identifier(name) string
  • sec: Pointer to endpoint security instance
  • pop: Pointer to proof of possession for authenticating a client

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.

Return
  • ESP_OK : Added new endpoint succesfully
  • ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist
  • ESP_ERR_INVALID_ARG : Null instance/name arguments
Parameters
  • pc: Pointer to the protocomm instance
  • ep_name: Endpoint identifier(name) string

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 verfied by clients through the endpoint.

Note
  • An endpoint must be bound to a valid protocomm instance, created using protocomm_new().
Return
  • ESP_OK : Added new security endpoint succesfully
  • 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
Parameters
  • pc: Pointer to the protocomm instance
  • ep_name: Endpoint identifier(name) string
  • version: Version identifier(name) string

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.

Return
  • ESP_OK : Added new endpoint succesfully
  • ESP_ERR_NOT_FOUND : Endpoint with specified name doesn’t exist
  • ESP_ERR_INVALID_ARG : Null instance/name arguments
Parameters
  • pc: Pointer to the protocomm instance
  • ep_name: Endpoint identifier(name) string

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

Structures

struct protocomm_security_pop

Proof Of Possession for authenticating a secure session.

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_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 implmentation

esp_err_t (*init)()

Function for initialising/allocating security infrastructure

esp_err_t (*cleanup)()

Function for deallocating security infrastructure

esp_err_t (*new_transport_session)(uint32_t session_id)

Starts new secure transport session with specified ID

esp_err_t (*close_transport_session)(uint32_t session_id)

Closes a secure transport session with specified ID

esp_err_t (*security_req_handler)(const protocomm_security_pop_t *pop, 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)(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)(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_security_pop protocomm_security_pop_t

Proof Of Possession for authenticating a secure session.

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

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.
Return
  • ESP_OK : Server started succefully
  • 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
Parameters
  • pc: Protocomm instance pointer obtained from protocomm_new()
  • config: Pointer to config structure for initialising HTTP server

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.

Return
  • ESP_OK : Server stopped succefully
  • ESP_ERR_INVALID_ARG : Null / incorrect protocomm instance pointer
Parameters
  • pc: Same protocomm instance that was passed to protocomm_httpd_start()

Structures

struct protocomm_httpd_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

Macros

PROTOCOMM_HTTPD_DEFAULT_CONFIG

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.

Return
  • ESP_OK : if successful
  • 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
Parameters
  • pc: Protocomm instance pointer obtained from protocomm_new()
  • config: Pointer to config structure for initialising BLE

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.
Return
  • ESP_OK : For success or appropriate error code
  • ESP_FAIL : Simple BLE stop error
  • ESP_ERR_INVALID_ARG : Null / incorrect protocomm instance
Parameters
  • pc: Same protocomm instance that was passed to protocomm_ble_start()

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

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_t

Config parameters for protocomm BLE service.

Public Members

char device_name[MAX_BLE_DEVNAME_LEN]

BLE device name being broadcast at the time of provisioning

uint8_t service_uuid[16]

SSID of the provisioning service

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

Macros

MAX_BLE_DEVNAME_LEN

BLE device name cannot be larger than this value

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.