Protocomm : Added component core for protocol communication

* This manages secure sessions and provides framework for multiple transports.
* The application can use protocomm layer directly to have application specific extensions for provisioning (or non-provisioning) use cases.
* Following features are available for provisioning :

  * Security - Security0 (no security), Security1 (curve25519 key exchange + AES-CTR encryption)
  * Proof-of-possession support for Security1

* Protocomm requires specific protocol buffer modules for compilation which can be generated from the `.proto` files in the `proto` directory using make.

Co-Authored-By: Amey Inamdar <amey@espressif.com>
Co-Authored-By: Anurag Kar <anurag.kar@espressif.com>

components/protocomm/include/security/protocomm_security.h

@@ -0,0 +1,93 @@
+// Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#pragma once
+
+#include <esp_err.h>
+
+/**
+ * @brief   Proof Of Possession for authenticating a secure session
+ */
+typedef struct protocomm_security_pop {
+    /**
+     * Pointer to buffer containing the proof of possession data
+     */
+    const uint8_t *data;
+
+    /**
+     * Length (in bytes) of the proof of possession data
+     */
+    uint16_t len;
+} protocomm_security_pop_t;
+
+/**
+ * @brief   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
+ */
+typedef struct protocomm_security {
+    /**
+     * Unique version number of security implmentation
+     */
+    int ver;
+
+    /**
+     * Function for initialising/allocating security
+     * infrastructure
+     */
+    esp_err_t (*init)();
+
+    /**
+     * Function for deallocating security infrastructure
+     */
+    esp_err_t (*cleanup)();
+
+    /**
+     * Starts new secure transport session with specified ID
+     */
+    esp_err_t (*new_transport_session)(uint32_t session_id);
+
+    /**
+     * Closes a secure transport session with specified ID
+     */
+    esp_err_t (*close_transport_session)(uint32_t session_id);
+
+    /**
+     * Handler function for authenticating connection
+     * request and establishing secure session
+     */
+    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);
+
+    /**
+     * Function which implements the encryption algorithm
+     */
+    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 decryption algorithm
+     */
+    esp_err_t (*decrypt)(uint32_t session_id,
+                         const uint8_t *inbuf, ssize_t inlen,
+                         uint8_t *outbuf, ssize_t *outlen);
+} protocomm_security_t;