JAVA Information Security Principles ad Practices Write a pr

JAVA

Information Security: Principles ad Practices.

Write a program to help an analyst decrypt a simple substitution cipher.

Your program should take the ciphertext as input, compute letter frequency

counts, and display these for the analyst. The program should

then allow the analyst to guess a key and display the results of the

corresponding \"decryption\" with the putative key.

BELOW IS WHAT I GOT SO FAR. ANALYST IS NOT GUESSING A KEY OR PUTATIVE KEY IS NOT COMING OUT.

IF YOU HAVE BETTER PROGRAM, PLEASE IGNORE THE SOURCE BELOW. THANKS.

import java.io.BufferedReader;

import java.io.InputStreamReader;

import java.util.HashMap;

import java.util.LinkedHashMap;

import java.util.Map;

public class SubstitutionCipher

{

Map<Character, Integer> letterFrequencyMap;

Map<Character, Character> key;

String ciphertext;

String plaintext;

BufferedReader br;

private void getCiphertext() // get cipher text as input from analyst

{

System.out.println(\"----- Substitution Cipher ----\");

System.out.println(\" Enter the cipher text: \");

br = new BufferedReader(new InputStreamReader(System.in));

try

{

ciphertext = br.readLine();

}

catch(Exception e)

{

System.err.println(\"Exception in cipher text reading \" + e );

e.printStackTrace();

}

ciphertext = ciphertext.toUpperCase();

System.out.println(\"The ciphertext Entered is - \" + ciphertext);

}

private void displayLetterFrequency()

{

letterFrequencyMap = new LinkedHashMap<Character, Integer>();

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

{

Character ch = ciphertext.charAt(i);

if (!( ch >= \'A\' && ch <=\'Z\')) continue; // check if letter is not in between A to Z

Integer cnt = (Integer) letterFrequencyMap.get(ch);

if(cnt == null)

{

letterFrequencyMap.put(ch,1);

}

else

{

letterFrequencyMap.put(ch,cnt + 1);

}

System.out.println(letterFrequencyMap);

}

private void keyGuess()

{

System.out.println(\"Hey Analyst , Guess a key from a to z\");

String putativeKey = null;

try

{

putativeKey = br.readLine();

}

catch(Exception e)

{

System.out.println(\"Excpetion in reading the putative key\");

e.printStackTrace();

}

createKeyMap(putativeKey);

}

private void createKeyMap(String putativeKey)

{

if(putativeKey.length() < 26)

{

System.out.println(\"putative key length is less then 26 letters. Invalid Entry. \");

return;

}

key = new HashMap<Character, Character>();

putativeKey = putativeKey.toUpperCase();

for(int j = 0;j<putativeKey.length();j++)

{

key.put(putativeKey.charAt(j), (char) (j + \'A\'));

}

private void getPlainText()

{

StringBuffer plainBuffer = new StringBuffer();

for( int k = 0; k < ciphertext.length(); k++)

{

Character chr = (Character) key.get(ciphertext.charAt(k));

if(chr == null)

{

System.out.println(\"Error Character - \"+ciphertext.charAt(k) + \"in ciphertext - is not mapped to any letter \");

plainBuffer.append(ciphertext.charAt(k));

}

else

{

plainBuffer.append(chr);

}

plaintext = plainBuffer.toString();

System.out.println(\"PlainText is - \" + plaintext);

}

private void closeInputbuffer()

{

if(br !=null)

{

try

{

br.close();

}

catch(Exception e)

{

System.out.println(\"Exception in closeInputbuffer \"+e);

e.printStackTrace();

}

public void decrypter()

{

try

{

getCiphertext();

displayLetterFrequency();

keyGuess();

getPlainText();

}

catch(Exception e)

{

System.out.println(\"Exception in Decryption \"+e);

e.printStackTrace();

}

finally

{

try

{

closeInputbuffer();

}

catch(Exception e)

{

System.out.println(\"Exception in closing input buffer\" +e);

e.printStackTrace();

}

public static void main(String[] args)

{

SubstitutionCipher cipher = new SubstitutionCipher();

cipher.decrypter();

}

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.Map;

class SubstitutionCipher
{
   Map<Character, Integer> letterFrequencyMap;
   Map<Character, Character> key;
   String ciphertext;
   String plaintext;
   BufferedReader br;
   private void getCiphertext() // get cipher text as input from analyst
   {
       System.out.println(\"----- Substitution Cipher ----\");
       System.out.println(\" Enter the cipher text: \");
       br = new BufferedReader(new InputStreamReader(System.in));
       try
       {
           ciphertext = br.readLine();
       }
       catch(Exception e)
       {
           System.err.println(\"Exception in cipher text reading \" + e );
           e.printStackTrace();
       }
       ciphertext = ciphertext.toUpperCase();
       System.out.println(\"The ciphertext Entered is - \" + ciphertext);
   }

   private void displayLetterFrequency()
   {
       letterFrequencyMap = new LinkedHashMap<Character, Integer>();
       for (int i = 0; i < ciphertext.length(); i++)
       {
           Character ch = ciphertext.charAt(i);
           if (!( ch >= \'A\' && ch <=\'Z\')) continue; // check if letter is not in between A to Z
               Integer cnt = (Integer) letterFrequencyMap.get(ch);
           if(cnt == null)
           {
               letterFrequencyMap.put(ch,1);
           }
           else
           {
               letterFrequencyMap.put(ch,cnt + 1);
           }
       }
       System.out.println(letterFrequencyMap);
   }

   private void keyGuess()
   {
       System.out.println(\"Hey Analyst , Guess a key from a to z\");
       String putativeKey = null;
       try
       {
           putativeKey = br.readLine();
       }
       catch(Exception e)
       {
           System.out.println(\"Excpetion in reading the putative key\");
           e.printStackTrace();
       }
       createKeyMap(putativeKey);
   }

   private void createKeyMap(String putativeKey)
   {
       if(putativeKey.length() < 26)
       {
           System.out.println(\"putative key length is less then 26 letters. Invalid Entry. \");
           return;
       }
       key = new HashMap<Character, Character>();
       putativeKey = putativeKey.toUpperCase();
       for(int j = 0;j<putativeKey.length();j++)
       {
           key.put(putativeKey.charAt(j), (char) (j + \'A\'));
       }
   }

   private void getPlainText()
   {
       StringBuffer plainBuffer = new StringBuffer();
       if(key== null)return;
       for( int k = 0; k < ciphertext.length(); k++)
       {

           Character chr = (Character) key.get(ciphertext.charAt(k));
           if(chr == null)
           {
               System.out.println(ciphertext);
               System.out.println(\"Error Character - \"+ciphertext.charAt(k) + \"in ciphertext - is not mapped to any letter \");
               plainBuffer.append(ciphertext.charAt(k));
           }
           else
           {
               plainBuffer.append(chr);
           }
       }
       plaintext = plainBuffer.toString();
       System.out.println(\"PlainText is - \" + plaintext);
   }

   private void closeInputbuffer()
   {
       if(br !=null)
       {
           try
           {
               br.close();
           }
           catch(Exception e)
           {
               System.out.println(\"Exception in closeInputbuffer \"+e);
               e.printStackTrace();
           }
       }
   }

   public void decrypter()
   {
       try
       {
           getCiphertext();
           displayLetterFrequency();
           keyGuess();
           getPlainText();
       }
       catch(Exception e)
       {
           System.out.println(\"Exception in Decryption \"+e);
           e.printStackTrace();
       }
       finally
       {
           try
           {
               closeInputbuffer();
           }
           catch(Exception e)
           {
               System.out.println(\"Exception in closing input buffer\" +e);
               e.printStackTrace();
           }
       }
   }
}