Y4xePHGs

1/*
2chat.cpp
3 
4What you type on one Arduino shows up in the screen
5attached to the other one and vice versa.
6*/
7#include <Arduino.h>
8 
9/* Calculates and returns (a**b) mod m.
10Parameters:
11  a: base, nonnegative integer
12  b: exponent, nonnegative integer, a=b=0 not allowed
13  m: positive integer
14*/
15uint32_t pow_mod( uint32_t a, uint32_t b, uint32_t m ) {
16  uint32_t result = 1;
17  for (uint32_t i=1; i<=b; ++i) {
18    Serial.print("Counter: ");
19    Serial.println(i);
20    Serial.print("Result: ");
21    Serial.println(result);
22    result = result * a;
23  }
24  result = result % m;
25  return result;
26}
27 
28void test_pow_mod_case( uint32_t a, uint32_t b, uint32_t m, uint32_t expresult ) {
29  uint32_t result = pow_mod( a, b, m );
30  Serial.print("Expected result: ");
31  Serial.println(expresult);
32  Serial.print("Computed result: ");
33  Serial.println(result);
34}
35 
36/* Tests pow_mod */
37void test_pow_mod() {
38  // test_pow_mod_case( 5, 10, 37, 30 );
39  // test_pow_mod_case( 8, 10, 37, 11 );
40  // Edge cases! Small values and big values
41  //
42  // test_pow_mod_case( 0, 10, 37, 0 );
43  // test_pow_mod_case( 8,  0, 37, 1 );
44 
45  test_pow_mod_case( 5, 20, 37, 12 );
46  // test_pow_mod_case( 5, 200, 37, 12 );
47}
48 
49/* Receives a number from the PC and returns it as a uint32_t number */
50uint32_t get_input() {
51  // TODO: Fix me!
52  return 0;
53}
54 
55int main() {
56  init();
57  Serial.begin(9600);
58  Serial3.begin(9600);
59  test_pow_mod();
60  while (true) {
61  }
62  uint32_t prime = 37;
63  uint32_t generator = 5;
64  uint32_t private_key = 10; // TODO: Fix this!!! generate this randomly
65  uint32_t public_key = pow_mod( generator, private_key, prime );
66  // key exchange:
67  Serial.print("Hey, here is the key you were looking for to share with your partner: ");
68  Serial.println(public_key);
69  Serial.print("Can you please enter the key received from your partner? ");
70  uint32_t partners_public_key = get_input();
71  uint32_t shared_secret = pow_mod( partners_public_key, private_key, prime );
72  char secret_key = shared_secret; // lowest 8 bits of the shared_secret
73 
74  while (true) {
75    // PC keystroke -> other Arduino
76    if (Serial.available()>0) {
77      char c = Serial.read();
78      // Serial.write(c); // echo back to screen
79      Serial.print("ASCII code of character to be sent: ");
80      Serial.println((int)c);
81      // encrypt data:
82      c = c ^ secret_key;
83      Serial.print("Encrypted information being sent: ");
84      Serial.println((int)c);
85      Serial3.write(c); // sending byte to the "other" Arduino
86    }
87    // Other Arduino to PC screen
88    if (Serial3.available()>0) {
89      char c = Serial3.read();
90      // decrypt data:
91      c = c ^ secret_key;
92      Serial.write(c); // show byte on screen as character
93    }
94  }
95 
96  Serial3.end();
97  Serial.end();
98  return 0;
99}