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/**@file
 *
 * @defgroup nrf_dfu_init_template Template file with an DFU init packet handling example.
 * @{
 *
 * @ingroup nrf_dfu
 *
 * @brief This file contains a template on how to implement DFU init packet handling.
 *
 * @details The template shows how device type and revision can be used for a safety check of the 
 *          received image. It shows how validation can be performed in two stages:
 *          - Stage 1: Pre-check of firmware image before transfer to ensure the firmware matches:
 *                     - Device Type.
 *                     - Device Revision.
 *                     Installed SoftDevice.
 *                     This template can be extended with additional checks according to needs.
 *                     For example, such a check could be the origin of the image (trusted source) 
 *                     based on a signature scheme.
 *          - Stage 2: Post-check of the image after image transfer but before installing firmware.
 *                     For example, such a check could be an integrity check in form of hashing or 
 *                     verification of a signature.
 *                     In this template, a simple CRC check is carried out.
 *                     The CRC check can be replaced with other mechanisms, like signing.
 *
 * @note This module does not support security features such as image signing, but the 
 *       implementation allows for such extension.
 *       If the init packet is signed by a trusted source, it must be decrypted before it can be
 *       processed.
 */

#include "dfu_init.h"
#include <stdint.h>
#include <string.h>
#include <dfu_types.h>
#include "nrf_error.h"
#include "crc16.h"

#define DFU_INIT_PACKET_EXT_LENGTH_MIN      2                       //< Minimum length of the extended init packet. The extended init packet may contain a CRC, a HASH, or other data. This value must be changed according to the requirements of the system. The template uses a minimum value of two in order to hold a CRC. */
#define DFU_INIT_PACKET_EXT_LENGTH_MAX      10                      //< Maximum length of the extended init packet. The extended init packet may contain a CRC, a HASH, or other data. This value must be changed according to the requirements of the system. The template uses a maximum value of 10 in order to hold a CRC and any padded data on transport layer without overflow. */

static uint8_t m_extended_packet[DFU_INIT_PACKET_EXT_LENGTH_MAX];   //< Data array for storage of the extended data received. The extended data follows the normal init data of type \ref dfu_init_packet_t. Extended data can be used for a CRC, hash, signature, or other data. */
static uint8_t m_extended_packet_length;                            //< Length of the extended data received with init packet. */


uint32_t dfu_init_prevalidate(uint8_t * p_init_data, uint32_t init_data_len)
{
    uint32_t i = 0;
    
    // In order to support signing or encryption then any init packet decryption function / library
    // should be called from here or implemented at this location.

    // Length check to ensure valid data are parsed.
    if (init_data_len < sizeof(dfu_init_packet_t))
    {
        return NRF_ERROR_INVALID_LENGTH;
    }

    // Current template uses clear text data so they can be casted for pre-check.
    dfu_init_packet_t * p_init_packet = (dfu_init_packet_t *)p_init_data;

    m_extended_packet_length = ((uint32_t)p_init_data + init_data_len) -
                               (uint32_t)&p_init_packet->softdevice[p_init_packet->softdevice_len];
    if (m_extended_packet_length < DFU_INIT_PACKET_EXT_LENGTH_MIN)
    {
        return NRF_ERROR_INVALID_LENGTH;
    }

    if (((uint32_t)p_init_data + init_data_len) < 
        (uint32_t)&p_init_packet->softdevice[p_init_packet->softdevice_len])
    {
        return NRF_ERROR_INVALID_LENGTH;
    }

    memcpy(m_extended_packet,
           &p_init_packet->softdevice[p_init_packet->softdevice_len],
           m_extended_packet_length);

/** [DFU init application version] */
    // To support application versioning, this check should be updated.
    // This template allows for any application to be installed. However, 
    // customers can place a revision number at the bottom of the application 
    // to be verified by the bootloader. This can be done at a location 
    // relative to the application, for example the application start 
    // address + 0x0100.
/** [DFU init application version] */
    
    // First check to verify the image to be transfered matches the device type.
    // If no Device type is present in DFU_DEVICE_INFO then any image will be accepted.
    if ((DFU_DEVICE_INFO->device_type != DFU_DEVICE_TYPE_EMPTY) &&
        (p_init_packet->device_type != DFU_DEVICE_INFO->device_type))
    {
        return NRF_ERROR_INVALID_DATA;
    }
    
    // Second check to verify the image to be transfered matches the device revision.
    // If no Device revision is present in DFU_DEVICE_INFO then any image will be accepted.
    if ((DFU_DEVICE_INFO->device_rev != DFU_DEVICE_REVISION_EMPTY) &&
        (p_init_packet->device_rev != DFU_DEVICE_INFO->device_rev))
    {
        return NRF_ERROR_INVALID_DATA;
    }

    // Third check: Check the array of supported SoftDevices by this application.
    //              If the installed SoftDevice does not match any SoftDevice in the list then an
    //              error is returned.
    while (i < p_init_packet->softdevice_len)
    {
        if (p_init_packet->softdevice[i]   == DFU_SOFTDEVICE_ANY ||
            p_init_packet->softdevice[i++] == SD_FWID_GET(MBR_SIZE))
        {
            return NRF_SUCCESS;
        }
    }
    
    // No matching SoftDevice found - Return NRF_ERROR_INVALID_DATA.
    return NRF_ERROR_INVALID_DATA;
}


uint32_t dfu_init_postvalidate(uint8_t * p_image, uint32_t image_len)
{
    uint16_t image_crc;
    uint16_t received_crc;
    
    // In order to support hashing (and signing) then the (decrypted) hash should be fetched and
    // the corresponding hash should be calculated over the image at this location.
    // If hashing (or signing) is added to the system then the CRC validation should be removed.

    // calculate CRC from active block.
    image_crc = crc16_compute(p_image, image_len, NULL);

    // Decode the received CRC from extended data.    
    received_crc = uint16_decode((uint8_t *)&m_extended_packet[0]);

    // Compare the received and calculated CRC.
    if (image_crc != received_crc)
    {
        return NRF_ERROR_INVALID_DATA;
    }

    return NRF_SUCCESS;
}