isc

//one time pad
#include<iostream>
#include<string.h>
using namespace std;

int main() {

    cout << "~~~~~~~~~~~~~~~~~~ Practical 5 ~~~~~~~~~~~~~~~~~~\n";
    cout << "|    Aim:  Perform encryption and decryption    |\n";
    cout << "|             using One Time Pad.               |\n";
    cout << "-------------------------------------------------\n";
    cout << "|          Made By: Arunesh Prasad (39)         |\n";
    cout << "-------------------------------------------------\n";
    int i, j, length,choice,lengthOfKey;
    char msg[100];
    char key[100];
    cout<<"| Enter the message: ";
    cin.getline(msg,100);
    length = strlen(msg);
    while(true){
        cout << "| Enter key with same lenth: ";
        cin >> key;
        lengthOfKey = strlen(key);
        if(lengthOfKey == length){
            cout << "-------------------------------------------------\n";
            break;
        }else{
            cout << "| Try again with same length! \n";
            cout << "-------------------------------------------------\n";
        }
    }
    cout <<"|  -> Enter your choice \n|    1. Encryption \n|    2. Decryption \n";
    cout << "|  -> Your choice: ";
    cin>>choice;
    if (choice==1){
      int chToIntInputText,chToIntInputKey;
      for(int i = 0; msg[i] != '\0'; ++i) {
         chToIntInputText = int(msg[i]);
         chToIntInputKey = int(key[i]);
         if (chToIntInputText >= 97 && chToIntInputText <= 122){
            chToIntInputText = chToIntInputText + chToIntInputKey;
            if (chToIntInputText > 122) {
               chToIntInputText = chToIntInputText - 97;
               chToIntInputText = chToIntInputText % 26;
               chToIntInputText = chToIntInputText + 97;
            }
            msg[i] = char(chToIntInputText);
         }
         else if (chToIntInputText >= 65 && chToIntInputText <= 90){
            chToIntInputText = chToIntInputText + chToIntInputKey;
            if (chToIntInputText > 90) {
               chToIntInputText = chToIntInputText - 65;
               chToIntInputText = chToIntInputText % 26;
               chToIntInputText = chToIntInputText + 65;
            }
            msg[i] = char(chToIntInputText);
         }
      }
      cout << "|  Encrypted message: " << msg << "\n";
      cout << "-------------------------------------------------\n";
   }
   else if(choice == 2) {
      int chToIntInputText,chToIntInputKey;
      for(int i = 0; msg[i] != '\0'; ++i) {
         chToIntInputText = char(msg[i]);
         chToIntInputKey = int(key[i]);
         if (chToIntInputText >= 97 && chToIntInputText <= 122){
            chToIntInputText = chToIntInputText - chToIntInputKey;
            if (chToIntInputText < 97) {
               chToIntInputText = -(chToIntInputText - 97);
               chToIntInputText = 26 - (chToIntInputText % 26);
               chToIntInputText = 97 + chToIntInputText;
            }
            msg[i] = char(chToIntInputText);
         }
         else if(chToIntInputText >= 65 && chToIntInputText <= 90){
            chToIntInputText = chToIntInputText - chToIntInputKey;
            if (chToIntInputText < 65) {
               chToIntInputText = -(chToIntInputText - 65);
               chToIntInputText = 26 - (chToIntInputText % 26);
               chToIntInputText = 90 - chToIntInputText;
            }
            msg[i] = char(chToIntInputText);
         }
      }
      cout << "|  Decrypted message: " << msg << "\n";
      cout << "-------------------------------------------------\n";
   }
}

//extended euclidean
#include <iostream>
#include <bits/stdc++.h>
#include <tuple>        
using namespace std;
 
//Recursive function to demonstrate the extended Euclidean algorithm
tuple<int, int, int> extended_gcd(int a, int b)
{
    if (a == 0) {
        return make_tuple(b, 0, 1);
    }
 
    int gcd, x, y;
 
    // unpack tuple returned by function into variables
    tie(gcd, x, y) = extended_gcd(b % a, a);
    return make_tuple(gcd, (y - (b/a) * x), x);
}
 
int main()
{
    int a, b;
    cout<<"\n--";
    cout << "\n\t\t+-----------------+" << endl;
	cout << "\t\t| Practical No. 6 |" << endl;
	cout << "\t\t+-----------------+" << endl;
	cout << "\t   BY : Jaanhavi Gautam [A_21]" << endl;
	cout << "\nAIM : Write a program to implement extended Euclidean Algorithm"<<endl;

    
    cout<<"\n\nEnter the first number: ";
    cin>>a;
    cout<<"\nEnter the second number: ";
    cin>>b;
 
    tuple<int, int, int> t = extended_gcd(a, b);
 
    int gcd = get<0>(t);
    int x = get<1>(t);
    int y = get<2>(t);

    cout << "The GCD is : " << gcd << endl;
    cout << "where, x = " << x << " and y = " << y << endl;
    cout << "The equation ax + by = gcd(a, b) will be" << endl;
    cout << a << "*" << x << " + " << b << "*" << y << " = " << gcd << endl;
 
    return 0;
}

//RSA
#include<iostream>
#include<math.h>
using namespace std;
int gcd(int a, int b) {
   int t;
   while(1) {
      t= a%b;
      if(t==0)
      return b;
      a=b;
      b=t;
   }
}
int main() {
   double p = 13;
   double q = 11;
   double n=p*q;//calculate phi
   double phi= (p-1)*(q-1);//calculate phi
   double e=7;
   double track;
   while(e<phi) {
      track = gcd(e,phi);
      if(track==1)
         break;
      else
      e++;
   }
   double d1=1/e;
   double d=fmod(d1,phi);
   double message = 9;
   double c = pow(message,e); //encrypt the message
   double m = pow(c,d);
   c=fmod(c,n);
   m=fmod(m,n);
   cout<<"A_21 Jaanhavi Gautam"<<endl;
   cout<<"Original Message = "<<message;
   cout<<"\n"<<"p = "<<p;
   cout<<"\n"<<"q = "<<q;
   cout<<"\n"<<"n = pq = "<<n;
   cout<<"\n"<<"phi = "<<phi;
   cout<<"\n"<<"e = "<<e;
   cout<<"\n"<<"d = "<<d;
   cout<<"\n"<<"Encrypted message = "<<c;
   cout<<"\n"<<"Decrypted message = "<<m;
   return 0;
}

//deffie-hellmen

#include<iostream>
#include<cstdio>
using namespace std;
class DiffieHellman
{
       public:
              long long int p,g,x,a,y,b,A,B;
              DiffieHellman(long long int p1,long long int g1,long long int x1,long long int y1)
              {
                     p = p1;
                     g = g1;
                     x = x1;
                     y = y1;
                     a=power(g,x,p);
                     b=power(g,y,p);
                     A = power(b,x,p);
                     B = power(a,y,p);
              }
              long long int power(int a,int b,int mod)
              {
                     long long int t;
                     if(b==1)
                           return a;
                     t=power(a,b/2,mod);
                     if(b%2==0)
                           return (t*t)%mod;
                     else
                           return (((t*t)%mod)*a)%mod;
int main()
{
       long long int p,g,x,a,y,b,A,B;
       cout<<"Executed by A_21 Jaanhavi Gautam"<<endl;
       cout<<"Enter the values of p and g upon which User A And User B both will aggree : "<<endl;
       cin>>p>>g;
       cout<<"Enter the Secret Integer for User A : ";
       cin>>x;
       cout<<"Enter the Secret Integer for User B : ";
       cin>>y;
       cout<<endl;
       DiffieHellman dh(p,g,x,y);
       cout<<"User A's private key, known only to User A : "<<dh.a<<endl;
       cout<<"User B's private key known only to User B : "<<dh.b<<endl;
       cout<<endl;
       cout<<"User A's public key, known to User A and User B : "<<dh.A<<endl;
       cout<<"User B's public key, known to User A and User B : "<<dh.B<<endl;
       return 0;
}