Cryptography

Cryptography

  1:14 PM    mayuravaani

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Crypto System

Cryptographic system are characterized along 3 independent dimensions

• The type of operation transforming plain text to cipher text
• The number of keys used
• The way in which plain text is processed.

Substitution techniques

• Caesar Cipher
• Monoalphabatic Cipher
• Playfair Cipher
• Hill Cipher
• Polyalphabatic Cipher

Transposition techniques

• Rail fence Cipher
• Columnar transposition 

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Cryptography : Caesar Cipher

Cryptography : Caesar Cipher

  1:12 PM    mayuravaani

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Caesar Cipher

Sample java code for Caesar Cipher

key : each letter shift of two in alphabet order
caesar cipher encryption

eg: hello -----------jgnnq
encryption

import java.util.*;

public class encryption{

public static void main(String args[]){

Scanner myScanner=new Scanner(System.in);

String alpha="abcdefghijklmnopqrstuvwxyz";

String word,text="";

System.out.println("Enter the plain text");

word=myScanner.nextLine().toLowerCase();

System.out.println("cipher text");

for(int i=0;i<word.length();i++){

boolean found=false;

char a=word.charAt(i);

int j=0;

while(j<alpha.length() && !found ){

char b=alpha.charAt(j);

if(a==' '){

text=text+" ";

found=true;

}

else if(a==b ){

found=true;

if(j<24){

text=text+alpha.substring(j+2,j+3);

}

else{

text=text+alpha.substring(j-alpha.length()+2,j-alpha.length()+3);

}

}

j++;

}

}

System.out.print(text);

}

}

output of the above code

   

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Cryptography : Vigenere Cipher

Cryptography : Vigenere Cipher

  1:06 PM    mayuravaani

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Vigenere Cipher

Sample java code for Vigenere Cipher

Encryption

//Vigenere cipher encryption
import java.util.*;
public class vigenere_encry{
public static void main(String args[]){
Scanner myscanner=new Scanner(System.in);
String alpha="abcdefghijklmnopqrstuvwxyz";
String keynew="",cipher="";
System.out.println("Enter the key");
String key=myscanner.nextLine().toLowerCase().replace(" ","");
System.out.println("Enter the plaintext");
String word=myscanner.nextLine().toLowerCase().replace(" ","");
int k=0;
while(k<word.length()/key.length()){
for(int i=0;i<key.length();i++){
keynew=keynew+key.charAt(i);
}
k++;
}

int q=0;
if(word.length()%key.length()!=0){
while(q<word.length()%key.length()){
keynew=keynew+key.charAt(q);
q++;
}
}
System.out.println("key       :"+keynew);
System.out.println("plaintext :"+word);

int numk=0,numw=0;
for(int i=0;i<word.length();i++){
char chark=keynew.charAt(i);
char charw=word.charAt(i);
for(int j=0;j<=25;j++){
if(chark==alpha.charAt(j)){
numk=j;
}
if(charw==alpha.charAt(j)){
numw=j;
}
}
cipher=cipher+alpha.charAt((numk+numw)%26);
}
System.out.println("ciphertext:"+cipher);
}
}

output of the above code

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Cryptography : Playfair Cipher

Cryptography : Playfair Cipher

  1:03 PM    mayuravaani

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Playfair Cipher

Sample java code for Playfair Cipher

Encryption

//playfair encryption: i and j count as one letter

import java.util.*;

public class playfair_encry{

public static void main(String args[]){

Scanner myscanner=new Scanner(System.in);

System.out.println("Enter the keyword");

String key=myscanner.nextLine().toLowerCase().replace(" ","").replace("j","i");

String alpha="abcdefghiklmnopqrstuvwxyz";

char array[][];

array=new char[5][5];

char arraykey[];

arraykey=new char[key.length()];

arraykey[0]=key.charAt(0);

int m=1;

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Cryptography : Railfence Cipher

Cryptography : Railfence Cipher

  1:00 PM    mayuravaani

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Railfence Cipher

Sample java code for Railfence Cipher

Key = 2
Encryption

//key=2
import java.util.Scanner;
public class Railfence_encry{
    public static void main(String args[]){
        Scanner myscanner =new Scanner(System.in);
        System.out.println("Enter the plaintext");
        String word=myscanner.nextLine().replace(" ","");
        System.out.println("cipher text");
        
        for(int i=0;i<word.length();i++){
            char a=word.charAt(i);
            if(i%2==0){
                System.out.print(a);
            }
        }
        

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Cryptography : Railfence Cipher

Cryptography : Railfence Cipher

  12:54 PM    mayuravaani

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Railfence Cipher

Sample java code for Railfence Cipher

Key = 3

Encryption

//key=3
import java.util.*;
public class Railfence1_encry{
    public static void main(String args[]){
        Scanner myscanner =new Scanner(System.in);
        System.out.println("Enter the plaintext");
        String word=myscanner.nextLine().replace(" ","").toLowerCase();
        System.out.println("cipher text");
int i=0;
String text1="",text3="";
while(i<word.length()){
char a=word.charAt(i);
text1=text1+a;
i=i+2;
if(i<word.length()){
a=word.charAt(i);
text3=text3+a;
}
i=i+2;
}
System.out.print(text1);
for(int j=1;j<word.length();j=j+2){
char a=word.charAt(j);
System.out.print(a);
}
System.out.println(text3);
    }
}
     

output of  the above code

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