Problem in a simple program

[techani]

hi , I have a problem in the following program (at the first link ) , which is : I send a simple encrypted message in AES , the encrypting and sending operations is done ok with no any problems , but when receiving and decrypting , the message decryption operation gives an exceptions , Although the decryption operation is done absolutely very well ( the second link improves that ) , some body tells me what is the problem Exactly please , thanks .

the first link :
RapidShare: Easy Filehosting

the second link :
RapidShare: Easy Filehosting

[r035198x]

What exception do you get at what line number? Post the line that is reported for the exception here.

[techani]

yes , these are the exceptions :

java.lang.NullPointerException
at trying.methodsForEncAndDec.AES_decrypt(methodsForE ncAndDec.java:83)
at trying.UDPServer.main(UDPServer.java:72)
Client send:
Exception in thread "main" java.lang.NullPointerException
at trying.methodsForEncAndDec.byte_deconcat(methodsFo rEncAndDec.java:123
)
at trying.UDPServer.main(UDPServer.java:80)
Press any key to continue...

[JosAH]

@techani
Read that stack trace: at line 83 of method AES_decrypt something was null while it shouldn't be (hence the thrown Exception). That method was called from line 72 in your main method (the next line in the stack trace).

Those lines should give you a clue about what was null. Check your own source.

kind regards,

Jos

[techani]

ya, I have checked , but i really wasn't able to know what is the wrong in the function AES_decrypt at the source code, because i don't see or even I can't see any runtime error there in that function , have you ever tried to execute the program in the second link ?! , then you will find that it does the encryption and the decryption operation very very well

Sooooo the problem surly absolutely is not at the (en-de)cryption operation

But although of that, the runtime error which the compiler Alleges in line 83 in the
AES_decrypt function, shows in some way that there is a problem in the key using operations(maybe ???), but i say again, the key using operation at the program in the second link(you should execute it to get more imagination about the problem) is the same using operations here in the main program, i don't know whats up ! . I really got so disappointed !!!!!!!!!!!!!!!!!!!!!!!!

[JosAH]

@techani
No I haven't; not many people like to be lured away in order to download something they don't know. Better post a short (compiling and running) example here in this forum that shows the unwanted behaviour. You'd get more and better responses then.

NullPointerExceptions can easily be pinned down with a couple of System.out.println() statements at crucial locations. Your stack trace helps here.

kind regards,

Jos

[techani]

ok , here take , this which was at the first link , my main program , three files :

methodsForEncAndDec.java :

package trying;
 
import java.util.*;
import java.io.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.lang.System.*;
import java.lang.*;
 
 
 
public class methodsForEncAndDec{
 
    public static int msglength;
    public static KeyPair key ;
    public static String AESinput_key;
 
 
    public methodsForEncAndDec(){}
 
 
 
public static byte[] SHA_hash(String text)
{
try{
    //hash
    MessageDigest md = MessageDigest.getInstance("SHA");
    byte[] hash_text = md.digest(text.getBytes());
    //print
/*    String hs = new sun.misc.BASE64Encoder().encode(hash_text);
    System.out.println("---> hash: <---");
    System.out.println(hs);*/
    return hash_text;
    }
catch( Exception e )
    {
      e.printStackTrace();
    }
    return null;
}
//#############################################################
public static byte[] AES_encrypt(byte[] plain_Text,String key)
{
try{
    // Key
    byte[] byte_key  = key.getBytes();
    SecretKeySpec final_key = new SecretKeySpec(byte_key,"AES");
 
    // ENCRYPTION
    Cipher m_encrypter = Cipher.getInstance("AES/ECB/PKCS5Padding");
    m_encrypter.init(Cipher.ENCRYPT_MODE , final_key);
    byte[] encrypted_Text = m_encrypter.doFinal(plain_Text);
 
    // unhide this if you want to see the sent message      
        /*System.out.println("---> After Encryption with AES: <---");
    for (int i=0 ; i<encrypted_Text.length ; i++)
    System.out.println((char)encrypted_Text[i]);
    */
 
    return encrypted_Text;
    }
    //catch exceptions  
catch( Exception e )
    {
      e.printStackTrace();
    }
    return null;
}    
//#############################################################
public static byte[] AES_decrypt(byte[] encrypted_Text,String key)
{
try{
    // Key
    byte[] byte_key  = key.getBytes();
    SecretKeySpec final_key = new SecretKeySpec(byte_key,"AES");
 
    // DECRYPTION
    Cipher m_decrypter = Cipher.getInstance("AES/ECB/PKCS5Padding");
    m_decrypter.init(Cipher.DECRYPT_MODE , final_key);
    byte[] decrypted_Text = m_decrypter.doFinal(encrypted_Text);
 
    // Print
/*    String dt = new sun.misc.BASE64Encoder().encode(decrypted_Text);
    System.out.println("---> After Decryption with AES: <---");
    System.out.println(dt);*/
 
    return decrypted_Text;
    }
    //catch exceptions  
catch( Exception e )
    {
      e.printStackTrace();
    }
    return null;
}    
//#############################################################
public static byte[] byte_concat(byte[] a , byte[] b)
{
    byte[] x = new byte[a.length + b.length];    
    for(int i=0 ; i<a.length ; i++)
    {
        x[i]=a[i];
    }
    for(int j=a.length ; j<x.length ; j++)
    {
        x[j]=b[j-a.length];
    }
    return x;
}
//#############################################################
public static byte[] byte_deconcat(byte[] a)
{
    //20 byte = 160bit = length of SHA hash to be deconcat
    byte[] x = new byte[a.length - 20];    
    for(int i=0 ; i<x.length ; i++)
    {
        x[i]=a[i];
    }
    //print
    System.out.println("---> After de-concat : <---");
    for (int i=0 ; i<x.length ; i++)
    {
        System.out.print((char)x[i]);
    }
    System.out.println("");
    return x;
}
 
}
 

UDPServer.java :

package trying;
 
 
import java.io.*; 
import java.net.*; 
import javax.swing.*;
import java.util.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.lang.System.*;
import java.lang.*;
 
 
public class UDPServer{
 
 
 
    public static void main(String args[]){ 
 
        //Create receiver Socket
        DatagramSocket aSocket = null;
 
 
        try{
            //1.create socket at agreed port
            aSocket = new DatagramSocket(1234); 
 
 
            //2. Define Receeiver Packet Size Size 
            byte[] buffer = new byte[methodsForEncAndDec.msglength];
 
 
 
Provider sunjce = new com.sun.crypto.provider.SunJCE();
Security.addProvider(sunjce);    
 
 
 
         // 3. Listening....
             while(true){
                 DatagramPacket request = new DatagramPacket(buffer, buffer.length);
                  aSocket.receive(request); 
 
 
 
 
//-------------------------------  Decryption operation with AES--------------------------------------------------------------------
 
 
 
    String recieved=new String(request.getData()).trim();
 
    char[] AES_encrypted_C=recieved.toCharArray();
 
    byte[] AES_encrypted_B=new byte[AES_encrypted_C.length];
 
for (int i=0 ; i<AES_encrypted_C.length ; i++)
    AES_encrypted_B[i]=(byte)AES_encrypted_C[i];
 
 
 
    // unhide the following(lines:66-68) if you want to see that the received message is as same as the sent one     
    /*
    System.out.println("---> After Recieving: <---");
    for (int i=0 ; i<AES_encrypted_B.length ; i++)
    System.out.println((char)AES_encrypted_B[i]);
    */
 
 
    byte [] AES_decrypted = methodsForEncAndDec.AES_decrypt(AES_encrypted_B,methodsForEncAndDec.AESinput_key);
 
 
 
//---------------------------------------------------------------------------------------------------------------------------------------------               
 
           System.out.println("Client send: ");
 
    byte [] AES_without_hash =methodsForEncAndDec.byte_deconcat(AES_decrypted);
 
 
            }
        }catch (SocketException e){System.out.println("Socket: " + e.getMessage());
        }catch (IOException e) {System.out.println("IO: " + e.getMessage());
        }finally {if(aSocket != null) aSocket.close();}
    }
}
 

UDPClient.java :

package trying;
 
import java.io.*; 
import java.net.*; 
import javax.swing.*;
import java.util.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.lang.System.*;
import java.lang.*;
 
 
 
public class UDPClient{
 
 
 
 
    public static void main(String args[]){ 
 
        DatagramSocket aSocket = null;
 
 
        try {
 
            // 1. Create Client Socket
            aSocket = new DatagramSocket(); 
 
 
 
//-------------------------------  Encryption operation with AES--------------------------------------------------------------------
 
//Declare SunJCE provider.
    Provider sunjce = new com.sun.crypto.provider.SunJCE();
      Security.addProvider(sunjce);
 
    //Get Plaintext
    Scanner my_object = new Scanner(System.in);
    System.out.println("---> Enter the plainText: <---");
    String plain = my_object.nextLine();
 
    //Hashing then Concatenating
    byte[] hash = methodsForEncAndDec.SHA_hash(plain);
    byte[] msg_with_hash = methodsForEncAndDec.byte_concat(plain.getBytes() , hash);
 
 
 
    //Get AES key
    System.out.println("---> Enter 16 characters key: <---");
    methodsForEncAndDec.AESinput_key/*String kyy */= my_object.nextLine();
 
    //AES encrypt
    byte [] AES_encrypted = methodsForEncAndDec.AES_encrypt(msg_with_hash,methodsForEncAndDec.AESinput_key/*kyy*/);
 
//convert into character array        
char[] AES_encrypted_C=new char[AES_encrypted.length];
for (int i=0 ; i<AES_encrypted.length ; i++)
        AES_encrypted_C[i]=(char)AES_encrypted[i];
 
//convert into string
String AES_encrypted_S=new String(AES_encrypted_C);
 
//then convert the string into array of bytes to be sent
byte[] AES_finalencrypted=AES_encrypted_S.getBytes();
 
 
//---------------------------------------------------------------------------------------------------------------------------------------------        
 
 
 
 
            //3.Define the server IP..    
               InetAddress aHost = InetAddress.getByName("localhost");//master
 
 
               //4. Attatch the socket to the Server Port..
            int serverPort =1234;    
 
 
 
            //5. define the packet to be sent to the server ...                                                     
            DatagramPacket request =
                 new DatagramPacket(AES_finalencrypted,AES_encrypted_S.length(), aHost, serverPort);
 
 
            //6. Send the Packet to the server...     
            aSocket.send(request);
 
 
        methodsForEncAndDec.msglength=AES_finalencrypted.length;
 
 
        }catch (SocketException e){System.out.println("Socket: " + e.getMessage());
        }catch (IOException e){System.out.println("IO: " + e.getMessage());
        }finally {if(aSocket != null) aSocket.close();}
    }                  
}
 

and this which was at the second link :

AES_SHA_RSA.java :

import java.util.*;
import java.io.*;
import java.security.*;
import java.security.spec.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.lang.System.*;
import java.lang.*;
 
/*Note 1 : I use 'Base64' to display cipher texts in terms
//of hex digits only , If you don't want to use it , you can
//do this : Scanner.out.println(new String(cipher_Text));
 
//Note 2 : input msg cannot be very long , because i don't
//use update() yet, if you want to input a msg with any
//length then use update() in conjunction with doFinal()
 
//Note 3 : it may be better to build a new function to initia-
//-lize the ciphers , i.e. to put the .getInstance() constru-
//-ctors there , so there will be only one instance of every
//cipher...
 
//Note 4 : the program firstly computes the hash of the msg , then //concatenates the hash to the msg , now we encrypt (using RSA or //AES ) the new msg. After decryption , it deconcatenates the hash to //obtain the original msg.
*/
 
public class AES_SHA_RSA
{
public static void main(String args[]) 
{
    //Declare SunJCE provider.
    Provider sunjce = new com.sun.crypto.provider.SunJCE();
      Security.addProvider(sunjce);
 
    //Get Plaintext
    Scanner my_object = new Scanner(System.in);
    System.out.println("---> Enter the plainText: <---");
    String plain = my_object.nextLine();
 
    //Hashing then Concatenating
    byte[] hash = SHA_hash(plain);
    byte[] msg_with_hash = byte_concat(plain.getBytes() , hash);
 
    //Get AES key
    System.out.println("---> Enter the 128-bit key: <---");
    String input_key = my_object.nextLine();
 
    //AES en(de)crypt
    byte [] AES_encrypted = AES_encrypt(msg_with_hash,input_key);
    byte [] AES_decrypted = AES_decrypt(AES_encrypted,input_key);
    byte [] AES_without_hash = byte_deconcat(AES_decrypted);
 
}//end 
 
 
 
 
//#############################################################
public static byte[] SHA_hash(String text)
{
try{
    //hash
    MessageDigest md = MessageDigest.getInstance("SHA");
    byte[] hash_text = md.digest(text.getBytes());
    //print
    String hs = new sun.misc.BASE64Encoder().encode(hash_text);
    System.out.println("---> hash: <---");
    System.out.println(hs);
    return hash_text;
    }
catch( Exception e )
    {
      e.printStackTrace();
    }
    return null;
}
//#############################################################
public static byte[] AES_encrypt(byte[] plain_Text,String key)
{
try{
    // Key
    byte[] byte_key  = key.getBytes();
    SecretKeySpec final_key = new SecretKeySpec(byte_key,"AES");
 
    // ENCRYPTION
    Cipher m_encrypter = Cipher.getInstance("AES/ECB/PKCS5Padding");
    m_encrypter.init(Cipher.ENCRYPT_MODE , final_key);
    byte[] encrypted_Text = m_encrypter.doFinal(plain_Text);
 
    // Print
    String ct = new sun.misc.BASE64Encoder().encode(encrypted_Text);
    System.out.println("---> After Encryption with AES: <---");
    System.out.println(ct);
 
    return encrypted_Text;
    }
    //catch exceptions  
catch( Exception e )
    {
      e.printStackTrace();
    }
    return null;
}    
//#############################################################
public static byte[] AES_decrypt(byte[] encrypted_Text,String key)
{
try{
    // Key
    byte[] byte_key  = key.getBytes();
    SecretKeySpec final_key = new SecretKeySpec(byte_key,"AES");
 
    // DECRYPTION
    Cipher m_decrypter = Cipher.getInstance("AES/ECB/PKCS5Padding");
    m_decrypter.init(Cipher.DECRYPT_MODE , final_key);
    byte[] decrypted_Text = m_decrypter.doFinal(encrypted_Text);
 
    // Print
    String dt = new sun.misc.BASE64Encoder().encode(decrypted_Text);
    System.out.println("---> After Decryption with AES: <---");
    System.out.println(dt);
 
    return decrypted_Text;
    }
    //catch exceptions  
catch( Exception e )
    {
      e.printStackTrace();
    }
    return null;
}    
//#############################################################
public static byte[] byte_concat(byte[] a , byte[] b)
{
    byte[] x = new byte[a.length + b.length];    
    for(int i=0 ; i<a.length ; i++)
    {
        x[i]=a[i];
    }
    for(int j=a.length ; j<x.length ; j++)
    {
        x[j]=b[j-a.length];
    }
    return x;
}
//#############################################################
public static byte[] byte_deconcat(byte[] a)
{
    //20 byte = 160bit = length of SHA hash to be deconcat
    byte[] x = new byte[a.length - 20];    
    for(int i=0 ; i<x.length ; i++)
    {
        x[i]=a[i];
    }
    //print
    System.out.println("---> After de-concat : <---");
    for (int i=0 ; i<x.length ; i++)
    {
        System.out.print((char)x[i]);
    }
    System.out.println("");
    return x;
}
 
}
 

and what do you mean by : can easily be pinned down with a couple of System.out.println() statements at crucial locations??? sorry i didn't understand , could you explain well please ??? thanks .

[r035198x]

@techani
That is not required. You were supposed to post only the lines at and just before the line reported for the exception by your stacktrace.



@techani
You have got to be kidding me.

[JosAH]

I wrote: "Better post a short (compiling and running) example here in this forum that shows the unwanted behaviour. You'd get more and better responses then."

kind regards,

Jos

[BSCode266]

I'm missing line numbers, what line is exactly 83?

[techani]

I'm very sorry for late , here is the line :


SecretKeySpec final_key = new SecretKeySpec(byte_key,"AES");

thanks.

[techani]

???????????????????????????????????????

[jkmyoung]

Try adding the following lines before that line:

if ( byte_key == null){
System.out.println("My program will die here");
}
 

Also please use code tags. eg [ code ] without the spaces [ / code]