unsigned char* hexstr_to_char(const char* hexstr)

{

    size_t len = strlen(hexstr);

    IF_ASSERT(len %  != )

        return NULL;

    size_t final_len = len / ;

    unsigned char* chrs = (unsigned char*)malloc((final_len+) * sizeof(*chrs));

    for (size_t i=, j=; j<final_len; i+=, j++)

        chrs[j] = (hexstr[i] %  + ) %  *  + (hexstr[i+] %  + ) % ;

    chrs[final_len] = '\0';

    return chrs;

}

int byteArrayToHexString(uint8_t *byte_array, int byte_array_len,

                         char *hexstr, int hexstr_len)

{

    int off = ;

    int i;

    for (i = ; i < byte_array_len; i ++) {

        off += snprintf(hexstr + off, hexstr_len - off,

                           "%02x", byte_array[i]);

    }

    hexstr[off] = '\0';

    return off;

}