Network Security. Various Protocols & Algorithms. A Practical HandBook for B.Sc IT Students.

1. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
IMPLEMENTING DIFFIE-HELMAN
The Diffie-Hellman protocol is a method for two computer users to generate a shared private key with
which they can then exchange information across an insecure channel. Let the users be named Alice and
Bob. First, they agree on two prime numbers and , where is large (typically at least 512 bits)
and is a primitive root modulo . (In practice, it is a good idea to choose such that is also
prime.) The numbers and need not be kept secret from other users. Now Alice chooses a large
random number as her private key and Bob similarly chooses a large number . Alice then
computes , which she sends to Bob, and Bob computes , which he sends to
Alice.
Now both Alice and Bob compute their shared key , which Alice computes as
and Bob computes as
Alice and Bob can now use their shared key to exchange information without worrying about other
users obtaining this information. In order for a potential eavesdropper (Eve) to do so, she would first
need to obtain knowing only , , and .
This can be done by computing from and from . This is the discrete
logarithmproblem, which is computationally infeasible for large . Computing the discrete logarithm of
a number modulo takes roughly the same amount of time as factoring the product of two primes the
same size as , which is what the security of the RSA cryptosystem relies on. Thus, the Diffie-Hellman
protocol is roughly as secure as RSA
The following java program shows the implementation of Diffie-Helman algorithm
import java.util.*;
import java.io.*;
public class Diffe
{
public static void main(String[] ar)
{
double a,b,k1,k2,x,y,n,g;
System.out.println("Enter Two Prime No:");
Scanner input = new Scanner(System.in);
System.out.print("N=");
n=input.nextDouble();
System.out.print("G=");
g=input.nextDouble();
System.out.println("Enter Random Number Of Allice And Bob:");
System.out.print("X=");
x=input.nextDouble();
System.out.print("Y=");
y=input.nextDouble();
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 1
Roll No of Student: 31 Date: __________

2. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
a=Math.pow(g,x)%n;
b=Math.pow(g,y)%n;
System.out.println("A:"+a);
System.out.println("B:"+b);
System.out.println("-------The Key Generated by Allice & Bob-------");
k1=Math.pow(b,x)%n;
System.out.println("K1:"+k1);
k2=Math.pow(a,y)%n;
System.out.println("K2:"+k2);
}
}
OUTPUT :
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 2
Roll No of Student: 31 Date: __________

3. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
PRACTICAL NO.2
import java.io.*;
import java.lang.*;
import java.util.*;
class RSA
{
public static void main(String[] args)
{
int p,q;
Scanner sc=new Scanner(System.in);
System.out.println("Prime Number");
p=sc.nextInt();
q=sc.nextInt();
int i=2;
for(i=2;i<=p-q;i++)
{
if(p-1.i==0)
{
System.out.println("Not a Prime Number");
break;
}
}
}
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 3
Roll No of Student: 31 Date: __________

4. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
if(i==p)
System.out.println("No: is a Prime Number");
for(i=2;i<=q-1;i++)
{
if(q%i==0)
{
System.out.println("Not a Prime Number");
break;
}
}
if(1==q)
System.out.println("No: is a Prime Number");
int n=(p*q);
System.out.println("Multiply"+n);
int fact=[(p-1)*(q-1)];
System.out.println(fact);
System.out.println("Enter e for RSA");
int e=sc.nextInt();
while(fact % e==0)
{
e=sc.nextInt();
}
System.out.println("fact is divisible by"+e);
int d;
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 4
Roll No of Student: 31 Date: __________

5. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
for(d=1;d<=fact;d++)
{
if((d*e)% fact==1)
{
System.out.println(d);
break;
}
}
System.out.println("Plain Text");
double pt=sc.nextInt();
double ct=(Math.Pow(pt,e)%n);
System.out.println(ct);
System.out.println("Send"+ct+"to receiver");
double ans= (Math.Pow(ct,d)%n);
System.out.println("pt"+ans);
}
}
OUTPUT
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 5
Roll No of Student: 31 Date: __________

6. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
IMPLEMENTING CAESAR CIPHER
In cryptography, a Caesar cipher, also known as Caesar's cipher, the shift cipher, Caesar's
code or Caesar shift, is one of the simplest and most widely known encryption techniques. It is a type
of substitution cipherin which each letter in the plaintext is replaced by a letter some fixed number of
positions down the alphabet. For example, with a left shift of 3, D would be replaced by A, E would
become B, and so on. The method is named after Julius Caesar, who used it in his private
correspondence.
The following java program shows the implementation of Caesar Cipher
import java.util.*;
class CaesarCipher
{
private final String ALPHABET = "abcdefghijklmnopqrstuvwxyz";
public String encrypt(String plainText,int shiftKey)
{
plainText = plainText.toLowerCase();
String cipherText="";
for(int i=0;i<plainText.length();i++)
{
int charPosition = ALPHABET.indexOf(plainText.charAt(i));
int keyVal = (shiftKey+charPosition)%26;
char replaceVal = this.ALPHABET.charAt(keyVal);
cipherText += replaceVal;
}
return cipherText;
}
public String decrypt(String cipherText, int shiftKey)
{
cipherText = cipherText.toLowerCase();
String plainText="";
for(int i=0;i<cipherText.length();i++)
{
int charPosition = this.ALPHABET.indexOf(cipherText.charAt(i));
int keyVal = (charPosition-shiftKey)%26;
if(keyVal<0)
{
keyVal = this.ALPHABET.length() + keyVal;
}
char replaceVal = this.ALPHABET.charAt(keyVal);
plainText += replaceVal;
}
return plainText;
}
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 6
Roll No of Student: 31 Date: __________

7. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
}
class CaesarDemo
{
public static void main(String args[])
{
Scanner sc=new Scanner(System.in);
System.out.print("Enter Plain Text :");
String plainText =sc.nextLine();
int shiftKey=3;
CaesarCipher cc = new CaesarCipher();
String cipherText = cc.encrypt(plainText,shiftKey);
System.out.println("Your Cipher Text :" + cipherText);
String cPlainText = cc.decrypt(cipherText,shiftKey);
System.out.println("Your Plain Text :" + cPlainText);
}
}
OUTPUT :
PRACTICAL NO.4
class RC4
{
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 7
Roll No of Student: 31 Date: __________

8. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
string str PlainText;
static char cipher[];
RC4(String str PlainText,int []key)
{
this.str PlainText=str PlainText;
int s[]=new int[255];
cipher =new char[str Plaintext.length()];
for(int i=0;i<s.length;i++)
{
s[i]=i;
}
int i=0;int j=0;
for(int k=0;k<str PlainText.length();k++)
{
int mod k=(k% key.length);
int kc= key[mod k];
j=(s[i]+j+kc)% 256+1;
int temp=s[i];
s[i]=s[j];
s[j]=temp;
int sc=(s[i]+s[j]%256);
int ck =(sc);
cipher[k]=(char)(ck^(int)str PlainText.charAt(k));
i=i+1;
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 8
Roll No of Student: 31 Date: __________

9. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
}
}
public static void main(String []args)
{
int K[]={1,2,3,4,5,6};
string str Original="HELLO WORLD";
System.out.println("Original String-->>"+str Original);
new RC4 (str Original,K);
for(int i=0;i<cipher.length i++)
{
System.out.println(""+cipher[i]);
}
}
}
}
IMPLEMENTING MONO-ALPHABETIC CIPHER
A mono-alphabetic cipher is a simple substitution cipher wherein each letter of the plaintext is replaced by
another letter in the ciphertext. An example of a mono-alphabetic cipher key follows:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
j r s q x z o e w n d y v p f a t b c i l h g k m u
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 9
Roll No of Student: 31 Date: __________

10. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
This key means that any 'j' in the plaintext will be replaced by an 'A' in the ciphertext, any 'r' in the
plaintext will be replaced by a 'B' in the ciphertext, and so on.
The following java program shows the implementation of Mono-alphaetic Cipher
class MonoAlphabetic {
private final String ALPHABET = "abcdefghijklmnopqrstuvwxyz";
private String newKey = "";
private static int isGenerated = 0;
private void generateKey(String userKey)
{
// removing duplicate charaters from user key
userKey = userKey.toLowerCase();
for(int i=0;i<userKey.length();i++)
{
int flag = 0;
for(int j=0;j<this.newKey.length();j++)
{
if(userKey.charAt(i)==newKey.charAt(j))
{
flag = 1;
break;
}
}
if(flag==0)
this.newKey += userKey.charAt(i);
}
if(isGenerated==0){
isGenerated = 1;
this.generateKey(this.newKey+""+this.ALPHABET);
}
}
public String encrypt(String plainText, String userKey)
{
this.generateKey(userKey);
String cipherText = "";
String tmpStr = plainText;
for(int i=0;i<plainText.length();i++)
{
char replaceVal = this.newKey.charAt(this.ALPHABET.indexOf(plainText.charAt(i)));
tmpStr = tmpStr.replace(tmpStr.charAt(i),replaceVal);
}
cipherText = tmpStr;
return cipherText;
}
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 10
Roll No of Student: 31 Date: __________

11. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
public String decrypt(String cipherText, String userKey)
{
this.generateKey(userKey);
String plainText = "";
String tmpStr = cipherText;
for(int i=0;i<cipherText.length();i++)
{
char replaceVal = this.ALPHABET.charAt(this.newKey.indexOf(cipherText.charAt(i)));
tmpStr = tmpStr.replace(tmpStr.charAt(i),replaceVal);
}
plainText = tmpStr;
return plainText;
}
}
class MonoAlphabeticDemo {
public static void main(String args[])
{
MonoAlphabetic ma = new MonoAlphabetic();
String en = ma.encrypt("hihowareyou","studentitzone");
String de = ma.decrypt(en,"studentitzone");
System.out.println(en + " - " + de);
}
}
OUTPUT:
IMPLEMENTING MODIFIED CAESAR CIPHER
In cryptography, a substitution cipher is a method of encoding by which units of plaintext are replaced
with cipher text, according to a regular system; the "units" may be single letters (the most common), pairs
of letters, triplets of letters, mixtures of the above, and so forth. The receiver deciphers the text by
performing an inverse substitution.
In Caesar cipher technique we displace the alphabets 3 places down the line, we can use a variant of
Caesar cipher where we can move any places up or down the line.
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 11
Roll No of Student: 31 Date: __________

12. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
The following java program shows the implementation of Modified Caesar Cipher
import java.util.Scanner;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
public class Caesar
{
public static void main(String[] args){
String cip=Caesar.encrypt();
Caesar.decrypt(cip);
}
private static String encrypt() {
char alphanum[]=
{'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','0','1','2','3','4', '5','6','7','8','9','
!','@','#','$','%','^','&','(',')','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','
Z','+','-','*','/','[',']','{','}','=','<','>','?','_'};
String empty = "empty";
Scanner input = new Scanner(System.in);
System.out.println("Enter the plaintext");
String plainText = input.nextLine();
String cipher = null;
char[] plain = plainText.toCharArray();
for(int i = 0;i<plain.length;i++){
for(int j = 0 ; j<85;j++){
if(j<=80){
if(plain[i]==alphanum[j]){
plain[i] = alphanum[j+5];
break;
}
}
else if(plain[i] == alphanum[j]){
plain[i] = alphanum [j-81];
}
}
}
cipher = String.valueOf(plain);
System.out.println(" cipher text is "+cipher);
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 12
Roll No of Student: 31 Date: __________

13. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
Scanner in = new Scanner(System.in);
System.out.println("To Decrypt plaintext enter 1");
int choice = in.nextInt();
if(choice == 1)
{
return cipher;
}
else
{
System.out.println("Thank you");
}
return empty;
}
private static String decrypt(String cip)
{
char alphanum[]
={'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','0','1','2','3','4','5','6','7','8','9'
,'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','!','@','#','$','%', '^','&','('
,')','+','-','*','/','[',']','{','}','=','<','>','?','_'};
String cipher = null;
String empty = "empty";
char[] cipher1 = cip.toCharArray();
if(cip .equals(empty))
{
System.out.println(" No text is Decrypted");
}
else
{
for(int i = 0;i<cipher1.length;i++)
{
for(int j = 0 ; j<85;j++)
{
if(j>=5 && cipher1[i]==alphanum[j])
{
cipher1[i] = alphanum[j-5];
break;
}
if(cipher1[i] == alphanum[j] && j<5){
cipher1[i] = alphanum[81+j];
break;
}
}
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 13
Roll No of Student: 31 Date: __________

14. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
}
}
cipher=String.valueOf(cipher1);
System.out.println(" Plain text is "+cipher);
return cipher;
}
}
OUTPUT :
IMPLEMENTING POLY-ALPHABETIC CIPHER
In a polyalphabetic cipher, multiple cipher alphabets are used. To facilitate encryption, all the alphabets
are usually written out in a largetable, traditionally called a tableau. The tableau is usually 26×26, so that
26 full ciphertext alphabets are available. The method of filling the tableau, and of choosing which
alphabet to use next, defines the particular polyalphabetic cipher. All such ciphers are easier to break
than once believed, as substitution alphabets are repeated for sufficiently large plaintexts.
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 14
Roll No of Student: 31 Date: __________

15. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
The following java program shows the implementation of Poly-alphabetic Cipher
package polyciipher;
import java.util.*;
public class PolyCiipher {
public static void main(String[] args) {
int[] j = new int[100];
int[] s = new int[100];
String test="";
try{
Scanner in = new Scanner(System.in);
System.out.println("Enter the plain text(STRING SHOULD BE IN UPPERCASE AND DONT GIVE SPACE
BETWEEN WORDS)::");
test = in.nextLine();
for ( int i = 0; i < test.length(); ++i ) {
char c = test.charAt( i );// "c" holds the individual character of the string
s[i] = (int) c-65;
}
for(int i=0;i<test.length()-1;i++){
j[i+1]=s[i];
}
System.out.println("Enter the key::");
int k = Integer.parseInt(in.nextLine());
j[0]=k;
System.out.println();
System.out.println("The position of the character in the cipher text::");
for(int i=0;i<test.length();i++){
j[i]=j[i]+s[i];
j[i]=j[i]%26;
System.out.print(j[i]);
}
System.out.println();
System.out.println("The cipher text::");
for(int i=0;i<test.length();i++){
char c=(char) (j[i]+65);
System.out.print(c);
}
System.out.println();
}
catch(Exception er){
System.out.println("--YOU HAVE TYPE INVALID DATA--");
}
}
}
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 15
Roll No of Student: 31 Date: __________

16. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
OUTPUT :
IMPLEMENTING RAIL-FENCE CIPHER
Rail Fence Cipher" (also called a zigzag cipher) generally refers to a form of transposition cipher. It
derives its name from the way in which it is encoded.
In the rail fence cipher, the plaintext is written downwards and diagonally on successive "rails" of an
imaginary fence, then moving up when we reach the bottom rail. When we reach the top rail, the
message is written downwards again until the whole plaintext is written out. The message is then read off
in rows
The following java program shows the implementation of Rail-fence Cipher
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 16
Roll No of Student: 31 Date: __________

17. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
import java.util.*;
public class railfence {
public static void main(String args[])
{
Scanner sc=new Scanner(System.in);
System.out.println("Enter Plain Text:");
String input =sc.nextLine();
String output = "";
int len = input.length(),flag = 0;
for(int i=0;i<len;i+=2) {
output += input.charAt(i);
}
for(int i=1;i<len;i+=2) {
output += input.charAt(i);
}
System.out.println("Ciphered Text : "+output);
}
}
OUTPUT:
IMPLEMENTING SIMPLE COLUMNAR CIPHER
In cryptography, a transposition cipher is a method of encryption by which the positions held by units
of plaintext (which are commonly characters or groups of characters) are shifted according to a regular
system, so that the ciphertext constitutes apermutation of the plaintext. That is, the order of the units is
changed. Mathematically a bijective function is used on the characters' positions to encrypt and
an inverse function to decrypt.
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 17
Roll No of Student: 31 Date: __________

18. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
In a columnar transposition, the message is written out in rows of a fixed length, and then read out
again column by column, and the columns are chosen in some scrambled order. Both the width of the
rows and the permutation of the columns are usually defined by a keyword. For example, the
word ZEBRAS is of length 6 (so the columns are of length 6), and the permutation is defined by the
alphabetical order of the letters in the keyword. In this case, the order would be "6 3 2 4 1 5".
In a regular columnar transposition cipher, any spare spaces are filled with nulls; in an irregular
columnar transposition cipher, the spaces are left blank. Finally, the message is read off in columns, in
the order specified by the keyword.
The following java program shows the implementation of Simple columnar Cipher
import java.io.*;
public class Play
{
static String s1,st,d;
static StringBuffer s;
static int m,n,c,choice,p,q,k;
static int z[]=new int[10];
static char a[][];
public static void dis()
{
System.out.println();
System.out.println("Matrix :");
System.out.println();
for(int i=0;i<m;i++)
{
for(int j=0;j<n;j++)
{
if(a[i][j]!='$')
System.out.print(a[i][j]+" ");
else
System.out.print(" ");
}
System.out.println();
}
System.out.println();
}
public static void enc(DataInputStream dis)throws Exception
{
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 18
Roll No of Student: 31 Date: __________

19. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
while(true)
{
c=0;
s1="";
System.out.println("------------------------------------------------------------------------ ");
System.out.print("Enter columns Sequence between 1 to "+n+" : ");
st=dis.readLine();
d=st+d;
System.out.println();
for(int i=0;i<n;i++)
{
c=(int)st.charAt(i)-49;
for(int j=0;j<m;j++)
{
if(a[j][c]!='$')
s1=s1+a[j][c];
}
}
s1.trim();
c=0;
for(int i=0;i<m;i++)
for(int j=0;j<n;j++)
if(c<s1.length())
a[i][j]=s1.charAt(c++);
else
a[i][j]='$';
dis();
System.out.println();
System.out.println();
System.out.print("Do You want to continue(yes(1)/no(0)) : ");
choice=Integer.parseInt(dis.readLine());
if(choice==0)
{
System.out.println("****************************************************************");
System.out.println();
System.out.println("Ecryption results in the ciphertext : "+s1);
System.out.println();
//System.exit(0);
return;
}
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 19
Roll No of Student: 31 Date: __________

20. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
}
}
public static void dec()
{
k=0;
p=s1.length()/n;
q=s1.length()%n;
//System.out.println("p = "+p+" q = "+q+" d = "+d);
for(int i=0;i<m;i++)
for(int j=0;j<n;j++)
a[i][j]='$';
for(int i=0;i<d.length();i++)
{
c=(int)d.charAt(i)-49;
//System.out.println("c = "+c);
if(c>=q)
{
for(int j=0;j<p;j++)
{
a[j][c]=s1.charAt(k++);
}
}
else
{
for(int j=0;j<p+1;j++)
{
a[j][c]=s1.charAt(k++);
}
}
dis();
if(k==s1.length())
{
s1="";
k=0;
for(int x=0;x<m;x++)
for(int j=0;j<n;j++)
if(a[x][j]!='$')
{
s1=s1+a[x][j];
a[x][j]='$';
}
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 20
Roll No of Student: 31 Date: __________

21. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
}
}
System.out.println("Decryption results in the plaintext : "+s1);
}
public static void main(String[] args)
{
try
{
DataInputStream dis=new DataInputStream(System.in);
System.out.print("Enter Plain text : ");
s1=dis.readLine();
s=new StringBuffer(s1);
//REMOVING WIDE-SPACES
for(int i=0;i<s.length();i++)
if(s.charAt(i)==' ')
s.deleteCharAt(i);
s1=new String(s);
d="";
System.out.println("Enter size of the array ");
System.out.print("Enter no of rows = ");
m=Integer.parseInt(dis.readLine());
System.out.print("Enter no of columns = ");
n=Integer.parseInt(dis.readLine());
a=new char[m][n];
c=0;
//ENTERING IN THE ARRAY
for(int i=0;i<m;i++)
for(int j=0;j<n;j++)
if(c<s1.length())
a[i][j]=s1.charAt(c++);
else
a[i][j]='$';
dis();
System.out.println("------------------------------------------------------------------------");
enc(dis);
System.out.println("-------------------------------Decryption-------------------------------");
dec();
}
catch(Exception e)
{}
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 21
Roll No of Student: 31 Date: __________

22. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
}
}
OUTPUT :
IMPLEMENTING VERNAM CIPHER
The Vernam Cipher is based on the principle that the plain text of a message is 'mixed' with random text
from a One Time Pad (OTP). Because the resulting cipher text is still truely random, it can safely be sent
over the air, without the risk of being deciphered by an interceptor. At the receiving end, the same OTP is
used to 'unmix' the random text from the cipher text, which results in the original plain text. One only
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 22
Roll No of Student: 31 Date: __________

23. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
has to guarantee that the OTP is safe, that there are only two copies of it, and that both copies are
destroyed immediately after use
The following java program shows the implementation of Vernam Cipher
//VernamCipher.java - cipher based on random pad
import java.io.*;
import java.util.*; //random number methods
class VernamCipher{
public static void main(String[] args)
throws IOException
{
if (args.length < 3) {
System.out.println("Usage: " +
"java VernamCipher clearFile codeFile key(an int)");
System.exit(1);
}
// open the input and output files
Scanner in = Scanner.create(new File(args[0]));
PrintWriter out = new PrintWriter(args[1]);
// use the key to start the pseudo-random sequence
Random r = new Random(Integer.parseInt(args[2]));
// encrypt one line at a time
while (in.hasNext()){
out.println(encrypt(in.nextLine(), r));
}
in.close();
out.close();
}
/**
Encrypt one string using a Vernam cipher.
@param message - a string to be encrypted
@param r - the source of random characters for
the encryption
@return the encrypted string
*/
public static String encrypt(String message,
Random r)
{
// for monitoring purposes print the unencrypted string
System.out.println(message);
char c;
// for efficiency use a StringBuffer instead of a String
StringBuffer cipher =
new StringBuffer(message.length());
for (int i = 0; i < message.length(); i++){
c = message.charAt(i);
if (Character.isLetter(c)) {
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 23
Roll No of Student: 31 Date: __________

24. AKBAR PEERBHOY COLLEGE OF COMMERCE AND ECONOMICS
T. Y. B. Sc. IT Network Security - Journal 2014-15
// for simplicity we only handle upper case letters
cipher.append( (char)
((Character.toUpperCase(c) - 'A' +
(int)(r.nextDouble() * 26)) % 26 + 'A'));
}
else {
// don't change non-letters
cipher.append(c);
}
}
String result = cipher.toString();
// for monitoring purposes print the encrypted string
System.out.println(result);
return result;
}
}
OUTPUT :
Name of Student: Fahad Shaikh Subject Teachers Sign: _____________ Page 24
Roll No of Student: 31 Date: __________