IS Lab C++

#HILL CIPHER
#include <bits/stdc++.h>
using namespace std;
vector<int> multiply(vector<vector<int>> mat,vector<int> vec){
    vector<int> ans(vec.size(),0);
    for(int i=0;i<mat.size();i++){
        for(int j=0;j<vec.size();j++){
            ans[i] += mat[i][j]*vec[j];
        }
        ans[i]%=26;
    }
    return ans;
}
int main() {
    string key,pt,ct;
    cin>>pt>>key;
    int n=key.size();
    n = ceil(sqrt(n)*1.0);
    vector<vector<int>> mat(n,vector<int>(n,0));
    int steps;
    steps =ceil( pt.size()/(n*1.0) );
    int counter=0;
    for(int i=0;i<n;i++){
        for(int j=0;j<n;j++){
            if(counter >= key.size()){
                mat[i][j]=25;
            }else{
                mat[i][j] = key[counter] - 'A';
            }
            counter++;
        }
    }
    for(int i=0;i<steps;i++){
        vector<int> vec(n);
        for(int j=0;j<n;j++){
            if(i*steps + j >= pt.size()){
                vec[j] = 25;
            }else{
                vec[j] = pt[i*steps + j] - 'A';
            }
        }
        auto temp = multiply(mat,vec);
        for(auto it:temp){
            ct+= (char)(it + 'A');
        }
    }
    cout<<ct;
}

--------------------------

#Play Fair Cipher

#include <bits/stdc++.h>
using namespace std;

int main() {
    string key,pt,ct;
    cin>>pt>>key;
    int n=key.size();
    vector<vector<int>> mat(5,vector<int>(5,0));
    map<char,int> mp;
    mp['J']=1;
    map<char,pair<int,int>> mp2;
    char t='A';
    int counter=0;
    for(int i=0;i<5;i++){
        for(int j=0;j<5;j++){
            while(counter<key.size() && mp[key[counter]]==1){
                counter++;
            }
            if(counter<key.size()){
                mp[key[counter]]=1;
                mat[i][j]=key[counter]-'A';
                mp2[key[counter]]={i,j};
                counter++;        
            }else{
                while(mp[t]==1){
                    t=t+1;
                }
                mp[t]=1;
                mat[i][j]=t-'A';
                mp2[t]={i,j};
            }
        }
    }
    mp2['J']=mp2['I'];
    cout<<"KEY MATRIX:\n";
    for(auto it:mat){
        for(auto itr:it){
            cout<<itr<<" ";
        }
        cout<<endl;
    }
    for(int i=0;i<pt.size();i+=2){
        int a,b;
        if(i+1<pt.size() && pt[i]!=pt[i+1]){
            if(mp2[pt[i]].first == mp2[pt[i+1]].first){
                a = mat[mp2[pt[i]].first][(mp2[pt[i]].second + 1)%5];
                b = mat[mp2[pt[i+1]].first][(mp2[pt[i+1]].second + 1)%5];
            }else if(mp2[pt[i]].second == mp2[pt[i+1]].second){
                
                a = mat[(mp2[pt[i]].first + 1)%5][mp2[pt[i]].second];
                b = mat[(mp2[pt[i+1]].first + 1)%5][mp2[pt[i+1]].second];
            }else{
                a = mat[mp2[pt[i]].first][mp2[pt[i+1]].second];
                b = mat[mp2[pt[i+1]].first][mp2[pt[i]].second];
            }

        }else{
            if(mp2[pt[i]].first == mp2['X'].first){
                a = mat[mp2[pt[i]].first][(mp2[pt[i]].second + 1)%5];
                b = mat[mp2['X'].first][(mp2['X'].second + 1)%5];
            }else if(mp2[pt[i]].second == mp2['X'].second){
                
                a = mat[(mp2[pt[i]].first + 1)%5][mp2[pt[i]].second];
                b = mat[(mp2['X'].first + 1)%5][mp2['X'].second];
            }else{
                a = mat[mp2[pt[i]].first][mp2['X'].second];
                b = mat[mp2['X'].first][mp2[pt[i]].second];
            }
            i--;
        }
        ct = ct + (char)(a+'A') + (char)(b+'A');
    }
    cout<<ct;
}

--------------------------------------------

#RC4


#include<bits/stdc++.h>
#include<time.h>
int n =256;
using namespace std;
void print(vector<int> arr){
    int n = arr.size();
    for(int i=0;i<n;i++){
        cout<<arr[i]<<" ";
    }
    cout<<endl;
}
int main(){

    srand(time(0));
    vector<int> s(n,0);
    for(int i=0;i<n;i++){
        s[i]=i;
    }
    int j=0;
    int i=0;
    vector<int> k(n);
    for(int i=0;i<n;i++){
        k[i]=(rand()+10)%50;
    }
    while(i<n){
        j=(j+s[i]+k[i])%n;
        swap(s[i],s[j]);
        i++;
    }
    i=0;
    j = 0;
    while(i<n){
        i++;
        j=(j+s[i])%n;
        swap(s[i],s[j]);
        int t = (s[i]+s[j])%n;
        k[i] = s[t];
    }
    vector<int> plain(n);
    for(int i=0;i<n;i++){
        plain[i]=(rand()+10)%50;
    }
    cout<<"plain text: ";
    print(plain);
    vector<int> cipher(n);
    for(int i=0;i<n;i++){
        cipher[i] = plain[i]^k[i];
    }
    cout<<"cipher text: ";
    print(cipher);
}

-----------------------------------------

#RSA

#include <bits/stdc++.h>
using namespace std;
int powerexp(int a,int x,int mod){
    int ans=1;
    for(int i=0;i<x;i++){
        ans = (ans%mod)*(a%mod);
    }
    return ans%mod;
}
int main(){
    double p,q;
    cout<<"Enter value of prime numbers p and q - ";
    cin>>p>>q;
    double n = p*q;
    cout<<"n = "<<n<<endl;
    double qn = (p-1)*(q-1);
    cout<<"qn = "<<qn<<endl;
    double e; // 1<e<qn such that gcd(e,qn) = 1
    for(double i = 2; i<qn; i++){
        if((int(qn))%int(i) != 0){
            e = i;
            break;
        }
    }
    cout<<"e = "<<e<<endl;
    double d; // de mod qn = 1
    for(int i=0;;i++){
        if((int(i*qn) + 1)%int(e) == 0){
            d = ((i*qn) + 1)/e;
            break;
        }
    }
    cout<<"d = "<<d<<endl;
    double M,C;
    cout<<"Data to be encrypted, M = ";
    cin>>M;
    C = powerexp(M,e,n);
    cout<<"\nCipher = "<<C;
    int M1 = powerexp(C,d,n);
    cout<<"\nDecrypted data, M1 = "<<M1<<endl;
    if(M==M1){
        cout<<"M == M1"<<endl;
    }
    return 0;
}

--------------------------------

#digital signature using RSA

#include <bits/stdc++.h>
using namespace std;
int powerexp(int a,int x,int mod){
    int ans=1;
    for(int i=0;i<x;i++){
        ans = (ans%mod)*(a%mod);
    }
    return ans%mod;
}
int main(){
    int p,q;
    cout<<"Enter value of prime numbers p and q - ";
    cin>>p>>q;
    int n = p*q;
    cout<<"n = "<<n<<endl;
    int qn = (p-1)*(q-1);
    cout<<"qn = "<<qn<<endl;
    int e; // 1<e<qn such that gcd(e,qn) = 1
    for(int i = 2; i<qn; i++){
        if((int(qn))%int(i) != 0){
            e = i;
            break;
        }
    }
    cout<<"e = "<<e<<endl;
    int d; // de mod qn = 1
    for(int i=0;;i++){
        if((int(i*qn) + 1)%int(e) == 0){
            d = ((i*qn) + 1)/e;
            break;
        }
    }
    cout<<"d = "<<d<<endl;
    int M,S;
    cout<<"Data to be encrypted, M = ";
    cin>>M;
    S = powerexp(M,d,n);
    cout<<"\n S = "<<S;
    int M1 = powerexp(S,e,n);
    cout<<"\n, M1 = "<<M1<<endl;
    if(M==M1){
        cout<<"M == M1"<<endl;
    }
    return 0;
}

#deffie helman
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
bool checkPrime(ll n)
{
if (n <= 1)
return false;
if (n == 2 || n == 3)
return true;
if (n % 2 == 0 || n % 3 == 0)
return false;
for (int i = 5; i <= sqrt(n); i = i + 6)
if (n % i == 0 || n % (i + 2) == 0)
return false;

return true;
}
ll power(ll a, ll b,ll P)
{
if (b == 1)
return a;
else
return (((ll)pow(a, b)) % P);

}

bool checkPrimitive(ll P,ll G){
unordered_set<ll>st;
ll t = 1;
st.insert(1);
for(int i = 1; i <= P - 2; i++){
t = (t % P * (G % P)) % P;
if(st.find(t) != st.end()) return false;
st.insert(t);
}
return st.size() == P - 1;
}

int main()
{

ll P;
cin>>P;
bool fl = checkPrime(P);
if(!fl){
cout<<"P is not Prime"<<"\n";
return 0;
}
cout << "The value of P : " << P << endl;
ll G;
cin>>G;
fl = checkPrimitive(P,G);
if(!fl){
cout<<"G is not a primitive root of P "<<"\n";
return 0;
}
cout << "The value of G : " << G << endl;

ll a = 4;
cout << "The private key a : " << a << endl;
ll x = power(G, a, P);

ll b = 3;
cout << "The private key b : " << b << endl;
ll y = power(G, b, P);

ll ka = power(y, a, P);
ll kb = power(x, b, P);
cout << "First Secret Key " << ka << endl;
cout << "Second Secret Key " << kb << endl;
return 0;
}