# Protocol Communication

[中文]

## Overview

The Protocol Communication (protocomm) component manages secure sessions and provides the framework for multiple transports. The application can also use the 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 the 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. Users can choose to implement their own security (even without using protobuf). Protocomm can also be used without any security layer.

Protocomm provides the framework for various transports:

- 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 for protocomm_security1 and protocomm_security2, the client still needs to establish sessions by performing the two-way handshake.

## Enabling Protocomm Security Version

The protocomm component provides a project configuration menu to enable/disable support of respective security versions. The respective configuration options are as follows:

> - Support `protocomm_security0`, with no security: CONFIG_ESP_PROTOCOMM_SUPPORT_SECURITY_VERSION_0, this option is enabled by default.

> - Support `protocomm_security1` with Curve25519 key exchange + AES-CTR encryption/decryption: CONFIG_ESP_PROTOCOMM_SUPPORT_SECURITY_VERSION_1, this option is enabled by default.

> - Support `protocomm_security2` with SRP6a-based key exchange + AES-GCM encryption/decryption: CONFIG_ESP_PROTOCOMM_SUPPORT_SECURITY_VERSION_2.

Note

Enabling multiple security versions at once offers the ability to control them dynamically but also increases the firmware size.

Warning

`protocomm_security0` provides no encryption or authentication and should not be used in production. `protocomm_security2` (SRP6a + AES-GCM) is the recommended security version for all production use cases.

## API Reference

### Header File

- components/protocomm/include/common/protocomm.h

- This header file can be included with:

  >     #include "protocomm.h"

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

  >     REQUIRES protocomm

  > or

  >     PRIV_REQUIRES protocomm

### 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

esp_err_t protocomm_get_sec_version(protocomm_t *pc, int *sec_ver, uint8_t *sec_patch_ver)

  Get the security version of the protocomm instance.

  This API will return the security version of the protocomm instance.

  Parameters:

    - pc -- [in] Pointer to the protocomm instance

    - sec_ver -- [out] Pointer to the security version

    - sec_patch_ver -- [out] Pointer to the security patch version

  Returns:

    - ESP_OK : Success

    - 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

- components/protocomm/include/security/protocomm_security.h

- This header file can be included with:

  >     #include "protocomm_security.h"

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

  >     REQUIRES protocomm

  > or

  >     PRIV_REQUIRES protocomm

### 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

  uint8_t patch_ver

    Patch 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

### Enumerations

enum protocomm_security_session_event_t

  Events generated by the protocomm security layer.

  These events are generated while establishing secured session.

  Values:

  enumerator PROTOCOMM_SECURITY_SESSION_SETUP_OK

    Secured session established successfully

  enumerator PROTOCOMM_SECURITY_SESSION_INVALID_SECURITY_PARAMS

    Received invalid (NULL) security parameters (username / client public-key)

  enumerator PROTOCOMM_SECURITY_SESSION_CREDENTIALS_MISMATCH

    Received incorrect credentials (username / PoP)

### Header File

- components/protocomm/include/security/protocomm_security0.h

- This header file can be included with:

  >     #include "protocomm_security0.h"

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

  >     REQUIRES protocomm

  > or

  >     PRIV_REQUIRES protocomm

### Header File

- components/protocomm/include/security/protocomm_security1.h

- This header file can be included with:

  >     #include "protocomm_security1.h"

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

  >     REQUIRES protocomm

  > or

  >     PRIV_REQUIRES protocomm

### Header File

- components/protocomm/include/security/protocomm_security2.h

- This header file can be included with:

  >     #include "protocomm_security2.h"

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

  >     REQUIRES protocomm

  > or

  >     PRIV_REQUIRES protocomm

### Header File

- components/protocomm/include/crypto/srp6a/esp_srp.h

- This header file can be included with:

  >     #include "esp_srp.h"

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

  >     REQUIRES protocomm

  > or

  >     PRIV_REQUIRES protocomm

### Functions

esp_srp_handle_t *esp_srp_init(esp_ng_type_t ng)

  Initialize srp context for given NG type.

  Note

  the handle gets freed with `esp_srp_free`

  Parameters:

    ng -- NG type given by `esp_ng_type_t`

  Returns:

    esp_srp_handle_t* srp handle

void esp_srp_free(esp_srp_handle_t *hd)

  free esp_srp_context

  Parameters:

    hd -- handle to be free

esp_err_t esp_srp_srv_pubkey(esp_srp_handle_t *hd, const char *username, int username_len, const char *pass, int pass_len, int salt_len, char **bytes_B, int *len_B, char **bytes_salt)

  Returns B (pub key) and salt. [Step2.b].

  Note

  *bytes_B MUST NOT BE FREED BY THE CALLER

  Note

  *bytes_salt MUST NOT BE FREE BY THE CALLER

  Parameters:

    - hd -- esp_srp handle

    - username -- Username not expected NULL terminated

    - username_len -- Username length

    - pass -- Password not expected to be NULL terminated

    - pass_len -- Password length

    - salt_len -- Salt length

    - bytes_B -- Public Key returned

    - len_B -- Length of the public key

    - bytes_salt -- Salt bytes generated

  Returns:

    esp_err_t ESP_OK on success, appropriate error otherwise

esp_err_t esp_srp_gen_salt_verifier(const char *username, int username_len, const char *pass, int pass_len, char **bytes_salt, int salt_len, char **verifier, int *verifier_len)

  Generate salt-verifier pair, given username, password and salt length.

  Note

  if API has returned ESP_OK, salt and verifier generated need to be freed by caller

  Note

  Usually, username and password are not saved on the device. Rather salt and verifier are generated outside the device and are embedded. this convenience API can be used to generate salt and verifier on the fly for development use case. OR for devices which intentionally want to generate different password each time and can send it to the client securely. e.g., a device has a display and it shows the pin

  Parameters:

    - username -- [in] username

    - username_len -- [in] length of the username

    - pass -- [in] password

    - pass_len -- [in] length of the password

    - bytes_salt -- [out] generated salt on successful generation, or NULL

    - salt_len -- [in] salt length

    - verifier -- [out] generated verifier on successful generation, or NULL

    - verifier_len -- [out] length of the generated verifier

  Returns:

    esp_err_t ESP_OK on success, appropriate error otherwise

esp_err_t esp_srp_set_salt_verifier(esp_srp_handle_t *hd, const char *salt, int salt_len, const char *verifier, int verifier_len)

  Set the Salt and Verifier pre-generated for a given password. This should be used only if the actual password is not available. The public key can then be generated using esp_srp_srv_pubkey_from_salt_verifier() and not esp_srp_srv_pubkey()

  Parameters:

    - hd -- esp_srp_handle

    - salt -- pre-generated salt bytes

    - salt_len -- length of the salt bytes

    - verifier -- pre-generated verifier

    - verifier_len -- length of the verifier bytes

  Returns:

    esp_err_t ESP_OK on success, appropriate error otherwise

esp_err_t esp_srp_srv_pubkey_from_salt_verifier(esp_srp_handle_t *hd, char **bytes_B, int *len_B)

  Returns B (pub key)[Step2.b] when the salt and verifier are set using esp_srp_set_salt_verifier()

  Note

  *bytes_B MUST NOT BE FREED BY THE CALLER

  Parameters:

    - hd -- esp_srp handle

    - bytes_B -- Key returned to the called

    - len_B -- Length of the key returned

  Returns:

    esp_err_t ESP_OK on success, appropriate error otherwise

esp_err_t esp_srp_get_session_key(esp_srp_handle_t *hd, char *bytes_A, int len_A, char **bytes_key, uint16_t *len_key)

  Get session key in `*bytes_key` given by len in `*len_key`. [Step2.c].

  This calculated session key is used for further communication given the proofs are exchanged/authenticated with `esp_srp_exchange_proofs`

  Note

  *bytes_key MUST NOT BE FREED BY THE CALLER

  Parameters:

    - hd -- esp_srp handle

    - bytes_A -- Private Key

    - len_A -- Private Key length

    - bytes_key -- Key returned to the caller

    - len_key -- length of the key in *bytes_key

  Returns:

    esp_err_t ESP_OK on success, appropriate error otherwise

esp_err_t esp_srp_exchange_proofs(esp_srp_handle_t *hd, char *username, uint16_t username_len, char *bytes_user_proof, char *bytes_host_proof)

  Complete the authentication. If this step fails, the session_key exchanged should not be used.

  This is the final authentication step in SRP algorithm [Step4.1, Step4.b, Step4.c]

  Parameters:

    - hd -- esp_srp handle

    - username -- Username not expected NULL terminated

    - username_len -- Username length

    - bytes_user_proof -- param in

    - bytes_host_proof -- parameter out (should be SHA512_DIGEST_LENGTH) bytes in size

  Returns:

    esp_err_t ESP_OK if user's proof is ok and subsequently bytes_host_proof is populated with our own proof.

### Type Definitions

typedef struct esp_srp_handle esp_srp_handle_t

  esp_srp handle as the result of `esp_srp_init`

  The handle is returned by `esp_srp_init` on successful init. It is then passed for subsequent API calls as an argument. `esp_srp_free` can be used to clean up the handle. After `esp_srp_free` the handle becomes invalid.

### Enumerations

enum esp_ng_type_t

  Large prime+generator to be used for the algorithm.

  Values:

  enumerator ESP_NG_3072

### Header File

- components/protocomm/include/transports/protocomm_httpd.h

- This header file can be included with:

  >     #include "protocomm_httpd.h"

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

  >     REQUIRES protocomm

  > or

  >     PRIV_REQUIRES protocomm

### 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()

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