text: // Copyright 2015-2016 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.
  #ifndef nvs_flash_h
  #define nvs_flash_h
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #include "nvs.h"
  #include "esp_partition.h"
  
  
  #define NVS_KEY_SIZE 32 // AES-256
  
  /**
   * @brief Key for encryption and decryption
   */
  typedef struct {
      uint8_t eky[NVS_KEY_SIZE]; /*!<  XTS encryption and decryption key*/
      uint8_t tky[NVS_KEY_SIZE]; /*!<  XTS tweak key */
  } nvs_sec_cfg_t;
  
  /**
   * @brief Initialize the default NVS partition.
   *
   * This API initialises the default NVS partition. The default NVS partition
   * is the one that is labeled "nvs" in the partition table.
   *
   * @return
   *      - ESP_OK if storage was successfully initialized.
   *      - ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages
   *        (which may happen if NVS partition was truncated)
   *      - ESP_ERR_NOT_FOUND if no partition with label "nvs" is found in the partition table
   *      - one of the error codes from the underlying flash storage driver
   */
  esp_err_t nvs_flash_init(void);
  
  /**
   * @brief Initialize NVS flash storage for the specified partition.
   *
   * @param[in]  partition_label   Label of the partition. Must be no longer than 16 characters.
   *
   * @return
   *      - ESP_OK if storage was successfully initialized.
   *      - ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages
   *        (which may happen if NVS partition was truncated)
   *      - ESP_ERR_NOT_FOUND if specified partition is not found in the partition table
   *      - one of the error codes from the underlying flash storage driver
   */
  esp_err_t nvs_flash_init_partition(const char *partition_label);
  
  /**
   * @brief Deinitialize NVS storage for the default NVS partition
   *
   * Default NVS partition is the partition with "nvs" label in the partition table.
   *
   * @return
   *      - ESP_OK on success (storage was deinitialized)
   *      - ESP_ERR_NVS_NOT_INITIALIZED if the storage was not initialized prior to this call
   */
  esp_err_t nvs_flash_deinit(void);
  
  /**
   * @brief Deinitialize NVS storage for the given NVS partition
   *
   * @param[in]  partition_label   Label of the partition
   *
   * @return
   *      - ESP_OK on success
   *      - ESP_ERR_NVS_NOT_INITIALIZED if the storage for given partition was not
   *        initialized prior to this call
   */
  esp_err_t nvs_flash_deinit_partition(const char* partition_label);
  
  /**
   * @brief Erase the default NVS partition
   *
   * This function erases all contents of the default NVS partition (one with label "nvs")
   *
   * @return
   *      - ESP_OK on success
   *      - ESP_ERR_NOT_FOUND if there is no NVS partition labeled "nvs" in the
   *        partition table
   */
  esp_err_t nvs_flash_erase(void);
  
  /**
   * @brief Erase specified NVS partition
   *
   * This function erases all contents of specified NVS partition
   *
   * @param[in]  part_name    Name (label) of the partition to be erased
   *
   * @return
   *      - ESP_OK on success
   *      - ESP_ERR_NOT_FOUND if there is no NVS partition with the specified name
   *        in the partition table
   */
  esp_err_t nvs_flash_erase_partition(const char *part_name);
  
  
  /**
   * @brief Initialize the default NVS partition.
   *
   * This API initialises the default NVS partition. The default NVS partition
   * is the one that is labeled "nvs" in the partition table.
   *
   * @param[in]  cfg Security configuration (keys) to be used for NVS encryption/decryption.
   *                              If cfg is NULL, no encryption is used.
   *
   * @return
   *      - ESP_OK if storage was successfully initialized.
   *      - ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages
   *        (which may happen if NVS partition was truncated)
   *      - ESP_ERR_NOT_FOUND if no partition with label "nvs" is found in the partition table
   *      - one of the error codes from the underlying flash storage driver
   */
  esp_err_t nvs_flash_secure_init(nvs_sec_cfg_t* cfg);
  
  /**
   * @brief Initialize NVS flash storage for the specified partition.
   *
   * @param[in]  partition_label   Label of the partition. Note that internally a reference to
   *                               passed value is kept and it should be accessible for future operations
   *
   * @param[in]  cfg Security configuration (keys) to be used for NVS encryption/decryption.
   *                              If cfg is null, no encryption/decryption is used.
   * @return
   *      - ESP_OK if storage was successfully initialized.
   *      - ESP_ERR_NVS_NO_FREE_PAGES if the NVS storage contains no empty pages
   *        (which may happen if NVS partition was truncated)
   *      - ESP_ERR_NOT_FOUND if specified partition is not found in the partition table
   *      - one of the error codes from the underlying flash storage driver
   */
  esp_err_t nvs_flash_secure_init_partition(const char *partition_label, nvs_sec_cfg_t* cfg);
  
  /**
   * @brief Generate and store NVS keys in the provided esp partition
   *
   * @param[in]  partition Pointer to partition structure obtained using
   *                       esp_partition_find_first or esp_partition_get.
   *                       Must be non-NULL.
   * @param[out] cfg       Pointer to nvs security configuration structure.
   *                       Pointer must be non-NULL.
   *                       Generated keys will be populated in this structure.
   *
   *
   * @return
   *      -ESP_OK, if cfg was read successfully;
   *      -or error codes from esp_partition_write/erase APIs.
   */
  
  esp_err_t nvs_flash_generate_keys(const esp_partition_t* partition, nvs_sec_cfg_t* cfg);
  
  
  /**
   * @brief Read NVS security configuration from a partition.
   *
   * @param[in]  partition Pointer to partition structure obtained using
   *                       esp_partition_find_first or esp_partition_get.
   *                       Must be non-NULL.
   * @param[out] cfg       Pointer to nvs security configuration structure.
   *                       Pointer must be non-NULL.
   *
   * @note  Provided parition is assumed to be marked 'encrypted'.
   *
   * @return
   *      -ESP_OK, if cfg was read successfully;
   *      -ESP_ERR_NVS_KEYS_NOT_INITIALIZED, if the partition is not yet written with keys.
   *      -ESP_ERR_NVS_CORRUPT_KEY_PART, if the partition containing keys is found to be corrupt
   *      -or error codes from esp_partition_read API.
   */
  
  esp_err_t nvs_flash_read_security_cfg(const esp_partition_t* partition, nvs_sec_cfg_t* cfg);
  
  #ifdef __cplusplus
  }
  #endif
  
  
  #endif /* nvs_flash_h */
  