Arduino to PC secure bluetooth connection - security

Question

I'm using an Arduino Uno to build a smoke detection system, which works. Since I have to do an IoT project, I have to establish a secure connection with a (for example) Web server, and I'm using a Bluetooth module HC-05 to do it. Now I want to encrypt and decrypt messages (which contain the values of the gas sensor) using an AES library.
That's my code on Arduino IDE:
#include <AES.h>
#include <AESLib.h>
#include <AES_config.h>
#include <xbase64.h>
#define VCC2 5
int smokeA0 = A0;
int buzzer = 11;
float sensorValue;
void setup() {
pinMode(buzzer, OUTPUT);
pinMode(smokeA0, INPUT);
pinMode(VCC2, OUTPUT);
digitalWrite(VCC2, HIGH);
Serial.begin(9600);
Serial.println("Gas sensor warning up!");
delay(2000); //allow the sensor to warm up
noTone(buzzer);
}
void loop() {
sensorValue = analogRead(smokeA0);
Serial.print("Sensor value: ");
Serial.print(sensorValue);
if(sensorValue > 300){
Serial.print(" | Smoke detected!");
tone(buzzer,1000,2000);
}
else {
noTone(buzzer);
}
Serial.println("");
delay(200); //wait 2s for next reading
}
How is the code through which I can encrypt the value sensor? And have I include it to the code above?
In the site file zip containing the informations of the project there's also this file called "Receiver", on Arduino IDE, too:
#include <SoftwareSerial.h>
#include <LiquidCrystal.h>
#include <AES.h>
AES aes ;
byte key [N_BLOCK] ;
byte cipher [N_BLOCK] ;
byte check [N_BLOCK] ;
#define PIN_EN 6
#define BUTTON 13
SoftwareSerial btSerial(4, 5);
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
String msg = "";
bool isConnected = false;
String readString = "";
byte msg_received[16];
char final_str[16];
void setup( )
{
Serial.begin(9600);
Serial.print("Receiving Application\n\n");
lcd.begin(16, 2);
lcd.setCursor(0,0);
lcd.print("Receiving App");
int bits = 128;
set_bits (bits, key, 0) ; // all zero key
byte succ;
succ = aes.set_key (key, bits) ;
if (succ != SUCCESS) Serial.println ("Failure set_key") ;
checkConnection();
if(!isConnected) {
pinMode(PIN_EN, OUTPUT); // this pin will pull the HC-010 EN HIGH to switch module to AT mode
digitalWrite(PIN_EN, HIGH);
Serial.println("Going in AT mode for BLE HC-10");
btSerial.begin(38400);
delay(1000);
pinMode(A0, INPUT);
while(!isConnected) {
if (btSerial.available()) {
char c = btSerial.read();
Serial.write(c);
}
if (Serial.available()) {
char c = Serial.read();
btSerial.write(c);
}
checkConnection();
}
btSerial.flush();
btSerial.end();
btSerial.begin(9600);
digitalWrite(PIN_EN, LOW);
Serial.println("Exiting from AT mode for BLE HC-10");
}
}
void checkConnection() {
int x = analogRead(A0);
if(x > 700) {
Serial.println("HC-10 is connected");
isConnected = true;
}
}
void loop( )
{
if(isConnected) {
getBTReply();
if(msg.length() > 0) {
Serial.println("Received msg: " + msg);
lcd.clear();
lcd.begin(16, 2);
lcd.setCursor(0,0);
lcd.print("Receiving App");
lcd.setCursor(0, 1);
lcd.print("Temp. > ");
lcd.print(msg);
lcd.setCursor(13, 1);
lcd.print(" C");
} else {
Serial.println("Received no msg");
lcd.clear();
lcd.begin(16, 2);
lcd.setCursor(0,0);
lcd.print("Receiving App");
lcd.setCursor(0, 1);
lcd.print("no message received");
}
}
delay(4000);
}
void getBTReply() {
msg = "";
int i = 0;
while (btSerial.available()) {
msg_received[i] = btSerial.read();
i++;
}
if (i==16) {
byte succ;
succ = aes.decrypt (msg_received, check) ;
if (succ != SUCCESS) Serial.println ("Failure decrypt") ;
String x = prs_byte_hex(check, 128);
textFromHexString(x.c_str(), final_str);
msg = String(final_str);
memset(final_str,0,strlen(final_str));
}
}
void set_bits (int bits, byte * a, int count)
{
bits >>= 3 ;
byte bcount = count >> 3 ;
for (byte i = 0 ; i < bcount ; i++)
a [i] = 0xFF ;
if ((count & 7) != 0)
a [bcount++] = 0xFF & (0xFF00 >> (count & 7)) ;
for (byte i = bcount ; i < bits ; i++)
a [i] = 0x00 ;
}
char * hex = "0123456789abcdef" ;
void print_value (byte * a, int bits)
{
bits >>= 3 ;
for (int i = 0 ; i < bits ; i++)
{
byte b = a[i] ;
// test purpose only
Serial.print (hex [b >> 4]) ;
Serial.print (hex [b & 15]) ;
}
Serial.println () ;
}
String prs_byte_hex (byte * a, int bits)
{
bits >>= 3 ;
String str_toparse;
for (int i = 0 ; i < bits ; i++)
{
byte b = a[i] ;
str_toparse += hex [b >> 4];
str_toparse += hex [b & 15];
}
return str_toparse;
}
void textFromHexString(char *hex, char *result)
{
char temp[3];
int index = 0;
temp[2] = '\0';
while (hex[index])
{
strncpy(temp, &hex[index], 2);
*result = (char)strtol(temp, NULL, 16);
result++;
index += 2;
}
*result = '\0';
}
So I don't need to build a Web Server in VSC to establish a connection through two devices?
If yes, can you please share me the code?
Sorry, I'm not very practical in IoT and I'm completely alone to do the project.

Answer 1

If you're sending data using the HC-05 to another arduino, then here is how to encrypt the data:
uint8_t key[] = {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15};
char data[] = "0123456789012345"; //16 chars == 16 bytes - Your data you want to send
aes128_enc_single(key, data);
Then on the receiving arduino
aes128_dec_single(key, data);
You send that data using serial. The receiving Arduino would also need an HC-05 module, or if you're sending to your computer, you can use a USB bluetooth adapter. You don't need a webserver to establish a connection between 2 arduinos, no. If you're sending data online, then you'll need to have a way to connect to the internet from one of your devices.