Internet Control Message Protocol (ICMP)

Why ICMP is important

IP protocol lacks error reporting mechanism and hosting/managing queries. To compensate ICMP protocol comes to the role as a companion to IP protocol giving following two services.

• Provides error reporting mechanism
• Hosts and manages queries

Did you have any doubt

ICMP is a network layer protocol as IP is, so one would suspect whether ICMP messages are passed directly to the data link layer. The answer is no. ICMP messages are first encapsulated inside ip datagram and then passed to the below data link layer. Following image clearly shows you how it happens.

Talking about ICMP messages

• Error reporting messages
ICMP acts as error reporting protocol it does not correct errors, error corrections are done by the higher level protocols. ICMP always sends the error messages to original source. There are five types of error messages as listed below.
• Destination unreachable
• Source quench
• Time exeeded
• Parameter problem
• Redirection
• Query messages
ICMP can also diagnose network problems through query messages. There are two pairs of query messages used for this purpose today.
• Echo request or reply
• Timestamp request or reply

Debugging tools that uses ICMP

ping

ping program can be used to find out whether a host is alive and responding. The source host sends an ICMP echo request message, if the destination host is alive it responds with ICMP echo reply messages.

traceroute

traceroute progam in unix or tracert in windows can be used to trace the route of a packet from source to destination.

Crypto Samples in java part four -Stream Cipher

SendStream.java

import java.io.FileOutputStream;
import java.io.ObjectOutputStream;

import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;

public class SendStream {
 
 public static void main(String[] args) {
  
  String data = "This have I thought good to deliver thee rrrr";
  
  //---------------Encryption ---------------------------------

  SecretKey key = null;

  try {
   KeyGenerator keygen = KeyGenerator.getInstance("DES");
   key = keygen.generateKey();

   Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
   cipher.init(Cipher.ENCRYPT_MODE, key);
   
   FileOutputStream fos = new FileOutputStream("cipher.file"); 
   CipherOutputStream cos = new CipherOutputStream(fos, cipher);
   ObjectOutputStream oos = new ObjectOutputStream(cos);   
   
   
   oos.writeObject(data);
   oos.flush();
   oos.close();
   
   
   FileOutputStream fosKey = new FileOutputStream("key.file"); 
   ObjectOutputStream oosKey = new ObjectOutputStream(fosKey); 
   oosKey.writeObject(key);
   oosKey.writeObject(cipher.getIV());

  } catch (Exception e) {
   e.printStackTrace();
  } 

 }

}

ReceiveStream.java

package ucsc.cipher;

import java.io.FileInputStream;
import java.io.ObjectInputStream;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;

public class RecieveStream {
 
 public static void main(String[] args) {
  SecretKey key = null;

  try {
   FileInputStream fisKey = new FileInputStream("key.file"); 
   ObjectInputStream oosKey = new ObjectInputStream(fisKey); 
   
   key =  (SecretKey)oosKey.readObject();
   
   byte[] iv = (byte[])oosKey.readObject();


   Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
   cipher.init(Cipher.DECRYPT_MODE, key, new IvParameterSpec(iv));
   
   FileInputStream fis = new FileInputStream("cipher.file"); 
   CipherInputStream cis = new CipherInputStream(fis, cipher);
   ObjectInputStream ois = new ObjectInputStream(cis);   
   
   
            System.out.println((String)ois.readObject());   
   
  } catch (Exception e) {
   e.printStackTrace();
  } 

  
 }

}

Crypto Samples in java part three - Symmetric key encryption

A secret key is generated and only known by the sender and the receiver. Sender encrypts the plain text in to cypher text using the shared key and sends it to the receiver. After Receiver receives the encrypted message he/she decrypts the message using the shared key and grabs the original plain text (have a look at the image for a better understanding).

import java.security.spec.AlgorithmParameterSpec;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;

public class SimpleCipher {

 public static void main(String[] args) {

  String data = "This have I thought good to deliver thee";

  // ---------------Encryption ---------------------------------

  byte[] encrypted = null;
  byte[] iv = null;
  SecretKey key = null;

  try {
   KeyGenerator keygen = KeyGenerator.getInstance("DES");/*
                 * get the key
                 * generator
                 * instance
                 */
   key = keygen.generateKey();// generate the secret key

   Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
   /*
    * get cipher engine instance.DES algorithm is used and it requires
    * the input data to be 8-byte sized blocks. To encrypt a plain text
    * message that is not multiples of 8-byte blocks, the text message
    * must be padded with additional bytes to make the text message to
    * be multiples of 8-byte blocks.PKCS5Padding has used for that
    * purpose. note that CBC is a block cipher mode therefore we need
    * an initialization vector to chain blocks.
    */

   cipher.init(Cipher.ENCRYPT_MODE, key);/*
             * initializing cipher engine
             * for encryption
             */

   encrypted = cipher.doFinal(data.getBytes());/* do the encryption */

   iv = cipher.getIV();/*
         * save the initialization vector, remember that
         * we need this only when we are using cipher
         * block chaining mode for encryption
         */

  } catch (Exception e) {
   e.printStackTrace();
  }

  // ---------------Decryption ---------------------------------

  try {

   Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");/*
                   * get
                   * cipher
                   * engine
                   * instance
                   */

   AlgorithmParameterSpec param = new IvParameterSpec(iv);/*
                  * set the
                  * vector
                  * value
                  */

   cipher.init(Cipher.DECRYPT_MODE, key, param);/*
               * initializing cipher
               * engine for decryption
               */

   byte[] decrypted = cipher.doFinal(encrypted);/*
               * obtain original plain
               * text
               */

   System.out.println(new String(decrypted));

  } catch (Exception e) {
   e.printStackTrace();
  }

 }

}