1.
[Type here] [Type here] Khushal Choudhary 8606
PRACTICAL NO. 1
Aim: Implementing Substitution Ciphers
a) Caesar Cipher
Code:
// Practical 1 A
import java.util.Scanner;
public class practical1a
{
int total_alphabets=26,key=3;
String encrypted=" ",decrypted=" ";
char ch; public String encrypt
(String plain)
{
for(int i=0;i<plain.length();i++)
{
ch=plain.charAt(i);
if(ch==' ') encrypted+="-";
else if(ch>='A' && ch<='Z')
{
if(ch<='Z'-key)
{
encrypted+=String.valueOf((char)(ch+key));
}
else {
encrypted+=String.valueOf((char)(ch-
(total_alphabetskey)));
}
} else
{
encrypted+=String.valueOf(ch);
}
}
return encrypted;
}
public String decrypt (String cipher)
{
for(int i=0;i<cipher.length();i++)
{
ch=cipher.charAt(i);
if(ch==' ') decrypted+="-";
else if(ch>='A' && ch<='Z')
{
if(ch>='A'+key)
{

2.
[Type here] [Type here] Khushal Choudhary 8606
decrypted+=String.valueOf((char)(ch-key));
}
else {
decrypted+=String.valueOf((char)(ch+(total_alphabetskey)));
}
} else
{
decrypted+=String.valueOf(ch);
}
}
return decrypted;
}
public static void main(String[] args)
{
String plaintext, ciphertext;
practical1a cc= new practical1a();
System.out.println("Enter text");
plaintext=new Scanner(System.in).nextLine().toUpperCase();
ciphertext=cc.encrypt(plaintext);
System.out.println("Encrypted text="+ciphertext);
plaintext=cc.decrypt(ciphertext);
System.out.println("Decrypted text="+plaintext);
} }
Output:
Modified Caesar Cipher
Code:

3.
[Type here] [Type here] Khushal Choudhary 8606
}
} else
{
decrypted+=String.valueOf(ch);
}
}
return decrypted;
}
public static void main(String[] args)
{
String plaintext, ciphertext;
int key; practical1b cc= new
practical1b();
System.out.println("Enter text");
plaintext=new Scanner(System.in).nextLine().toUpperCase();
System.out.println("Enter key "); key=new
Scanner(System.in).nextInt();
ciphertext=cc.encrypt(plaintext,key);
System.out.println("Encrypted text="+ciphertext);
plaintext=cc.decrypt(ciphertext,key);
System.out.println("Decrypted text="+plaintext);
}
}
Output:
Monoalphabetic

4.
[Type here] [Type here] Khushal Choudhary 8606
Code:
}
Output:
d) Poly-Alphabetic
Code:
import java.util.*;
public class Poly
{
public static void main(String[]args)
{
String plaintext="HOWAREYOU";
String secretkey="HELLOHELL";
System.out.println("Plain text before
encryption:"+plaintext);
String encryptedtext=encrypt(plaintext,secretkey);
System.out.println("Encrypted text after
encryption:"+encryptedtext);
String
decryptedtext=decrypt(encryptedtext,secretkey);
System.out.println("Decrypted text after
decryption:"+decryptedtext);
}
private static String encrypt(String plaintext, String
secretkey) {
StringBuffer encryptedString=new
StringBuffer(); int encryptedInt;
for(int i=0;i<plaintext.length();i++)
{ int
plaintextInt=(int)(plaintext.charAt(i));
int secretkeyInt=(int)(secretkey.charAt(i));
encryptedInt=(plaintextInt+secretkeyInt)%26;
encryptedString.append((char)((encryptedInt)+(int)'A'));
}
return encryptedString.toString();
}
private static String decrypt(String decryptedtext, String
secretkey) {

5.
[Type here] [Type here] Khushal Choudhary 8606
StringBuffer decryptedString=new
StringBuffer(); int decryptedInt;
for(int i=0;i<decryptedtext.length();i++)
{
int
decryptedtextInt=(int)(decryptedtext.charAt(i));
int secretkeyInt=(int)(secretkey.charAt(i));
decryptedInt=decryptedtextInt-secretkeyInt;
if(decryptedInt<0)
Output: