Cryptography Lab Work (in JAVA)

Program No. # 1

//To find whether a number is prime or not

import java.io.*;
class prime1
{
 public static void main(String args[]) throws IOException
 {
  int i;
  System.out.print("Enter a number: ");
  BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  int num=Integer.parseInt(br.readLine());
  int flag=0;
      for(i=2;i<=num/2;i++)
      {
        if(num%i==0)
        {
        flag=1;
        System.out.println("The number is not prime");
        break;
                 }
       }
        if(flag==0)
        System.out.print("The number is prime");
      System.out.println("");
  }
}






Program No. # 2


//To find prime numbers between 1 to 100


class prime2
{
 public static void main(String args[])
 {
   int i,j;
   System.out.println("The prime numbers between 1 to 100 are: ");
   for(i=2;i<100;i++)
   {
      int flag=0;
      for(j=2;j<=i/2;j++)
      {
        if(i%j==0)
        {
        flag=1;
        break;
                }
        }
        if(flag==0)
        System.out.print(i+" ");
    }
    System.out.println("");
  }
}





Program No. # 3

//To find factors of a number

import java.io.*;
public class factor
{
      public static void main(String[] args) throws IOException
      {
       System.out.print("Enter the number:  ");
       BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
          long n = Long.parseLong(br.readLine());
               System.out.print("The prime factorization of " + n + " is:   ");

              // for each potential factor i
             for (long i = 2; i <= n / i; i++)
              {
                // if i is a factor of N, repeatedly divide it out
                   while (n % i == 0)
                  {
                    System.out.print(i + " , ");
                    n = n / i;
                  }
              }

            // if biggest factor occurs only once, n > 1
               if (n > 1) System.out.println(n);
               else       System.out.println();
           }
 }





Program No. # 4

//To find gcd of two numbers

import java.io.*;
class gcd1
{
 public int gcd(int x, int y)
 {
     int g=0;
     if(x<0)
     x=-x;
     if(y<0)
     y=-y;
     while(x>0)
     {
         g=x;
         x=y%x;
         y=g;
     }
     return(g);
 }
 public static void main(String args[]) throws IOException
 {
  int i;
  System.out.print("Enter first number: ");
  BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  int num1=Integer.parseInt(br.readLine());
  System.out.print("Enter first number: ");
  int num2=Integer.parseInt(br.readLine());
  gcd1 a=new gcd1();
  int g1=a.gcd(num1,num2);
  System.out.println("The GCD of "+num1+" & "+num2+" is "+g1);
 }
}





Program No. # 5

//To find gcd of two numbers using recursion

import java.io.*;
class gcd2
{
   public int gcd(int x, int y)
   {
     int g,f;
     if(x<0)
     x=-x;
     if(y<0)
     y=-y;
 g=x;
 f=y%x;
     if(f>0)
     return gcd(f,g);    //recursive call of gcd method
     return(g);
    }
  public static void main(String args[]) throws IOException
  {
  int i;
  System.out.print("Enter first number: ");
  BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  int num1=Integer.parseInt(br.readLine());
  System.out.print("Enter first number: ");
  int num2=Integer.parseInt(br.readLine());
  gcd2 a=new gcd2();
  int g1=a.gcd(num1,num2);
  System.out.println("The GCD of "+num1+" & "+num2+" is "+g1);
  }
}





Program No. # 6

//Caesar Cipher of Strings without key


class caesar1
{
public static void main(String args[])
{

  String a="abcdefghijklmnopqrstuvwxyz";
  String pt="hello";
  System.out.println("The plain text is:  "+pt.toUpperCase());
  int len=pt.length();
  System.out.print("The corresponding cipher text is:    ");
  for(int i=0;i<len;i++)
{
char s1= pt.charAt(i);
int j=a.indexOf(s1);
String ct=a.substring(j+3,j+4);
System.out.print(ct.toUpperCase());
}
       System.out.println(" ");
}
}





Program No. # 7

//Caesar Cipher of Strings with key

import java.io.*;
class caesar2
{
public static void main(String args[]) throws IOException
{

  String a="abcdefghijklmnopqrstuvwxyz";
  String pt="saurabh";
  System.out.println("The plain text is:  "+pt.toUpperCase()); //plain text
  System.out.print("Enter the key:  ");
  BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
  int key=Integer.parseInt(br.readLine());
  int len=pt.length();
  System.out.print("The cipher text is:  ");
  for(int i=0;i<len;i++)
  {
   char s1= pt.charAt(i);
   //System.out.println(s1);
   int j=a.indexOf(s1);
   int m=(j+key)%26;
   String ct=a.substring(m,m+1);
   System.out.print(ct.toUpperCase());
  }
System.out.println("");
}
}






Program No. # 8

//Columnar Transposition without key

class TransCol
{
   public static void  main(String a[]) throws ArrayIndexOutOfBoundsException
   {
    int k=0;
    String pt="mynameissarkar";
    System.out.println("Plain text: MY NAME IS SARKAR");
    String[][] pt1=new String[5][5];
    for(int i=0;i<5;i++)
      {
       for(int j=0;j<5;j++)
        {
          if(k>=pt.length())
           {
     break;
           }
        pt1[i][j]=pt.substring(k,k+1);
        k++;
       }
       System.out.println("");
     }


//Matrix representation
      for(int i=0;i<5;i++)
     {
       for(int j=0;j<5;j++)
       {
    if(pt1[i][j]!=null)
    {
              System.out.print(pt1[i][j]+"                ");
            }
            else
           {
            System.out.print("X"+"                ");
           }
       }
       System.out.println("");
       System.out.println("");
   }


 //Cipher text
 System.out.print("The cipher text is:   ");
 for(int i=0;i<5;i++)
   {
     for(int j=0;j<5;j++)
     {
     if(pt1[j][i]!=null)
     {
              System.out.print(pt1[j][i].toUpperCase());
            }
           else
           {
             System.out.print("X");
           }
      }
    }
    System.out.println("   ");
  }
}






Program No. # 9

//Columnar Transposition with key

class TransColKey
{
  public static void  main(String a[]) throws ArrayIndexOutOfBoundsException
  {
     int k=0;
     int[] key={3,1,0,4,2};
     String pt="mynameissarkar";
     System.out.print("Plain text: MY NAME IS SARKAR");
     String[][] pt1=new String[5][5];
     for(int i=0;i<5;i++)
     {
       for(int j=0;j<5;j++)
       {
         if(k>=pt.length())
          {
     break;
          }
          pt1[i][j]=pt.substring(k,k+1);
          k++;
       }
      System.out.println("");
     }

//Key Used
System.out.print("The Key used is: [  ");
for(int i=0;i<5;i++)
System.out.print(key[i]+"  ");
System.out.println("]");

//Matrix representation
   for(int i=0;i<5;i++)
  {
    for(int j=0;j<5;j++)
     {
    if(pt1[i][j]!=null)
    {
             System.out.print(pt1[i][j]+"                ");
            }
           else
           {
            System.out.print("X"+"                ");
            }
       }
      System.out.println("");
      System.out.println("");
   }


//Cipher text
System.out.print("The cipher text is:   ");
 for(int i=0;i<5;i++)
   {
      int m=key[i];
      for(int j=0;j<5;j++)
        {
     if(pt1[j][m]!=null)
     {
              System.out.print(pt1[j][m].toUpperCase());
            }
            else
           {
              System.out.print("X");
           }
        }
     }
     System.out.println("   ");
  }
}






Program No. # 10

//PlayFair with key

import java.io.*;
class PlayFair
{
  public static void  main(String a[]) throws ArrayIndexOutOfBoundsException,IOException
  {

   String[][] pt1=new String[5][5];
   String all="ABCDEFGHIKLMNOPQRSTUVWXYZ";
   String key="MONARCHY";
   System.out.print("Enter the plain text:  ");
   BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
   String pt=br.readLine();
   pt=pt.toUpperCase();
   if((pt.length()%2!=0))
   pt=pt+"X";
   System.out.println("The plain text is:  "+pt);
   String ct="";
   int len2,k=0;
   int len1=key.length();
   for(int i=0;i<len1;i++)
   {
       len2=all.length();
       String s=key.substring(i,i+1);
       if(s.equals("J"))
         {
          s="I";
         }
       int n=all.indexOf(s);
       all=all.substring(0,n)+""+all.substring(n+1,len2);
   }
   all=key+""+all;

   //Preparing the playfair matrix
   System.out.println("The playfair matrix is:");
   for(int i=0;i<5;i++)
     {
      for(int j=0;j<5;j++)
      {
       if(k>=all.length())
       {
        break;
       }
       pt1[i][j]=all.substring(k,k+1);
       k++;
      }
      System.out.println("");
     }


   //Array representation
     for(int i=0;i<5;i++)
    {
     for(int j=0;j<5;j++)
     {
       System.out.print(pt1[i][j]+"                ");
     }
     System.out.println("");
    }



   for(k=0;k<pt.length();k=k+2)
    {
    int i,j,a1=0,b=0,c=0,d=0;
    String s=pt.substring(k,k+2);
    String s1=s.substring(0,1);
    String s2=s.substring(1,2);
    /*if(s1.equals(s2))
    {
        if(pt.length()%2==0 && pt.charAt(pt.length()-1)=='X')
        pt=pt.substring(0,pt.length()-1);
      pt=pt.substring(0,k+1)+"X"+pt.substring(k+1,pt.length()-1);
      continue;
    }
    */
    for(i=0;i<5;i++)
    {
        for(j=0;j<5;j++)
        {
            if(pt1[i][j].equals(s1))
            {
                a1=i;
                b=j;

                break;
            }
        }
    }
    for(i=0;i<5;i++)
        {
            for(j=0;j<5;j++)
            {
                if(pt1[i][j].equals(s2))
                {
                    c=i;
                    d=j;
                    break;
                }
            }
    }

    if(a1==c)
    {
        if((b+1)>=5)
        b=0;
        if((d+1)>=5)
        d=0;
    s1=pt1[a1][b+1];
    s2=pt1[a1][d+1];
    }
    if(b==d)
    {
        if((a1+1)>=5)
        a1=0;
        if((c+1)>=5)
        c=0;
    s1=pt1[a1+1][b];
    s2=pt1[c+1][b];
    }
    if(a1!=c && b!=d)
    {
        s1=pt1[a1][d];
        s2=pt1[c][b];
    }
    ct=ct+""+s1+""+s2;

}
System.out.println("The cipher text is:  "+ct);
}
}







Program No. # 11

//RSA Public key encryption

import java.io.*;
class check
{
    // method to check whether a number is prime or not
    void prime(int p,int q)
    {

        for(int i=2;i<=p/2;i++)
         {
          if(p%i==0)
          {
            System.out.println("p is not prime");
            System.exit(0);
          }
          }
          for(int i=2;i<=q/2;i++)
           {
          if(q%i==0)
          {
            System.out.println("q is not prime");
            System.exit(0);
          }
        }

    }

    // method to find GCD of two numbers
    public int gcd(int x, int y)
     {
         int g,f;
         if(x<0)
         x=-x;
         if(y<0)
         y=-y;
        g=x;
        f=y%x;
        if(f>0)
        return gcd(f,g);    //recursive call of gcd method
         return(g);
     }
}


class RSA
{
    public static void main(String args[]) throws IOException
    {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Enter P: ");
        int p=Integer.parseInt(br.readLine());
        //System.out.println();
        System.out.print("Enter Q: ");
        int q=Integer.parseInt(br.readLine());

        //check p,q are prime or not
        check ob=new check();
        ob.prime(p,q);
        int n=p*q;
        int z=(p-1)*(q-1);
        //System.out.println();
        System.out.print("Enter Encrytion key(e): ");
        int e=Integer.parseInt(br.readLine());

        //check whether e and z are relatively prime
        int g=ob.gcd(e,z);
        if(g!=1)
        {
            System.out.println("e and z are not relatively prime");
            System.exit(0);
        }
        int d=1;
        while(((e*d)%z)!=1)
        d++;
        System.out.print("Enter the plain text: ");
        int m=Integer.parseInt(br.readLine());
        int c=(m^e)%n;
        System.out.println("The decryption key is(d) : "+d);
        System.out.println("The cipher text is : "+c);
    }
}





Program No. # 12

//Blum Blum Shub Generator

import java.io.*;
class check
{
    // method to check whether a number is prime or not
    void prime(int p,int q)
    {

        for(int i=2;i<=p/2;i++)
         {
          if(p%i==0)
          {
            System.out.println("p is not prime");
            System.exit(0);
          }
          }
          for(int i=2;i<=q/2;i++)
           {
          if(q%i==0)
          {
            System.out.println("q is not prime");
            System.exit(0);
          }
        }

    }

    // method to find GCD of two numbers
    public int gcd(int x, int y)
     {
         int g,f;
         if(x<0)
         x=-x;
         if(y<0)
         y=-y;
        g=x;
        f=y%x;
        if(f>0)
        return gcd(f,g);    //recursive call of gcd method
         return(g);
     }
}


class BBS
{
    public static void main(String args[]) throws IOException
    {
        int i;
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Enter prime no. P congruent to 3mod4: ");
        int p=Integer.parseInt(br.readLine());
        //System.out.println();
        System.out.print("Enter prime no. Q congruent to 3mod4: ");
        int q=Integer.parseInt(br.readLine());

        //check p,q are prime or not
        check ob=new check();
        ob.prime(p,q);

        //check whether p,q are congruent to 3mod4 or not
        if(p%4!=3)
        {
            System.out.println("P is not congruent to 3mod4");
            System.exit(0);
        }
        if(q%4!=3)
        {
            System.out.println("Q is not congruent to 3mod4");
            System.exit(0);
        }

        int n=p*q;
        //System.out.println();
        System.out.print("Enter a random vaue s: ");
        int s=Integer.parseInt(br.readLine());

        //check whether s and n are relatively prime
        int g=ob.gcd(s,n);
        if(g!=1)
        {
            System.out.println("s and n are not relatively prime");
            System.exit(0);
        }
        int[] x=new int[100];
        int[] B=new int[100];
        x[0]=(s*s)%n;
        System.out.println("");
        System.out.print("i"+"       "+"Xi"+"       "+"Bi");
        System.out.println("");
        System.out.println("");
        for(i=1;i<=20;i++)
        {
            x[i]=(x[i-1]*x[i-1])%n;
            B[i]=x[i]%2;
            System.out.print(i+"       "+x[i]+"       "+B[i]);
            System.out.println("");
        }
    }
}







Program No. # 13

//Linear Congruential Generators

import java.io.*;
class LCG
{
    public static void main(String args[]) throws IOException
    {
        int i;
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Enter the modulus(m): ");
        int m=Integer.parseInt(br.readLine());
        System.out.print("Enter the multiplier(a): ");
        int a=Integer.parseInt(br.readLine());
        System.out.print("Enter the increment value(c): ");
        int c=Integer.parseInt(br.readLine());
        int[] x=new int[100];
        System.out.print("Enter the seed value(Xo): ");
        x[0]=Integer.parseInt(br.readLine());
        System.out.print("Enter how many random numbers to generate(n): ");
        int n=Integer.parseInt(br.readLine());
        System.out.println("");
        System.out.print("The Sequence generated is:-  ");

        //Iterative function to generate random numbers
        for(i=1;i<=n;i++)
        {
            x[i]=(a*x[i-1]+c)%m;
            System.out.print(x[i]+" , ");
        }
        System.out.println("");
        System.out.println("");
    }
}






Program No. # 14

//Middle Square Method to generate random numbers


import java.io.*;
class midsq
{
    public static void main(String args[]) throws IOException
    {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    System.out.print("Enter a four digit number(r): ");
    int r= Integer.parseInt(br.readLine());
    int[] x=new int[100];
    String[] s=new String[100];
    System.out.print("Enter how many random numbers to generate(n):");
    int n= Integer.parseInt(br.readLine());
    int i,j,k;
    x[0]=r;
    System.out.println("The random numbers thus generated are:-");
    for(i=1;i<=n;i++)
    {
        x[i]=x[i-1]*x[i-1];
        s[i]=Integer.toString(x[i]);  //the number is converted to string
        int len=s[i].length();
        //Padding 0 in front of a number if its length is less than 8
        if(len<8)
        {
            j=8-len;
            for(k=0;k<j;k++)
            {
                s[i]="0"+s[i];
            }
        }

        //rejecting first 2 & last 2 digits of the number
        s[i]=s[i].substring(2,6);
        System.out.print(i+".    "+s[i]);
        System.out.println("");
        x[i]=Integer.parseInt(s[i]);
     }
     }
}