Programming Question

please follow the ins

CSCI 3171 NETWORK COMPUTING
Assignment No. 3
Date Given: Sunday, October 24th, 2021
Due: Saturday, November 6th, 2021, 11.59 PM
Exercise 1: The objective of this exercise is to implement a Client-Server application that exchanges
messages that are encrypted using Caesar cipher. It focuses on developing Client-Server applications using
Java socket programming. Please read the lecture notes on Network Programming. Follow these steps:
a. Go to Brightspace -> Content -> Lecture Modules -> Module 3 -> Module 3-Part 5.
Download two files.
• EchoServer.java
• EchoClient.java
b. Caesar cipher is a simple alphabetic cipher that shifts the letters of the alphabet
by k letters to the right where k is the “secret” key known only to the sender and
the receiver. For example, if k = 3, the word “Java” will be encoded as “Mdyd”. As
another example, “ZEBRA” will be encrypted as “CHEUD” (notice that we
wraparound to the beginning of the alphabet from Z).
c. You are to write a client-server program in which the communication starts by
the client asking the server for the key. A key (an integer between 1 and 25) is
randomly generated by the server and sent to the client. (In practice, keys are
transferred using a secure protocol, but for now to keep it simple we will just
transfer the key in plain text). Then every message that is sent from the client to
the server must be encrypted using this key. Again, for the sake of simplicity,
assume that only uppercase and lowercase letters are transmitted (no numbers or
special characters). The message must be decrypted by the server and displayed.
When the client enters “Bye”, the connection terminates.
d. Provide three test cases for your program and take a screenshot of each test case.
An example of the three test cases is shown below.
Exercise 2: Now that you have seen how a simple encryption algorithm works, in this exercise you will conduct
the wireshark analysis of a secure application layer protocol, SSH (Secure Shell).
a. Start Wireshark capture.
b. Connect to the timberlea.cs.dal.ca server using SSH from your terminal window.
For this you would open a command window/Terminal, enter
ssh -l timberlea.cs.dal.ca
and enter your CS password. Then log out. Stop Wireshark capture.
c. Set the filter to ssh and provide a screen capture of the Wireshark interaction.
d. Identify and report some of the important SSH protocol messages.
e. Show the content of one encrypted packet.
f. Set the filter to tcp.port== and provide a screen captureof the
Wireshark interaction.
g. Identify the TCP SYN, SYN-ACK and ACK segments and the FIN-ACK and ACK segments before the
start of the SSH session and the end of the SSH session,respectively.
Note: The objective of this question is to get an overview of SSH. It is not necessary foryou at this point to
understand the details of the encryption mechanisms and the key exchange algorithms used in SSH.
Submission:
Submit one zip file containing the following:
a) Commented CaesarCipherServer.java and CaesarCipherClient.java source codes for Exercise 1.
d) One word/text/pdf document containing the following:
i) Test cases with outputs of your program run for Exercise 1.
ii) Screenshot of the ssh dialog on the terminal window for Exercise 2.
iii) Screenshot of the Wireshark captures for Exercise 2.
iv) Answers to questions d, e and g in Exercise 2 (either marked on the screenshot or written
separately)
Ensure that your Name and Banner ID appears as comments on top of each of the source code files. Also ensure that your
Name and Banner ID appears on top of the word/text/pdf document.
Note: You must submit .java files so that the TAs are able to run your codes.
Late Submission Penalty: The assignment is due on Saturday at 11.59 PM. Late submissions up to 5 hours
(4.59 AM on Sunday) will be accepted without penalty. After that, there will be a 10% late penalty per day on
the mark obtained. For example, if you submit the assignment on Sunday at 12 noon and your score is 8/10,
it will be reduced to 7.2/10. Submissions past five days after the grace submission time will not be accepted.
import java.io.*;
import java.net.*;
public class EchoClient{
public static void main(String[] args) throws IOException{
Socket link = null;
PrintWriter output = null;
BufferedReader input = null;
try{
link = new Socket(“127.0.0.1”, 50000);
output = new PrintWriter(link.getOutputStream(), true);
input = new BufferedReader(new
InputStreamReader(link.getInputStream()));
}
catch(UnknownHostException e)
{
System.out.println(“Unknown Host”);
System.exit(1);
}
catch (IOException e){
System.out.println(“Cannot connect to host”);
System.exit(1);
}
BufferedReader stdIn = new BufferedReader(new
InputStreamReader(System.in));
String usrInput;
while ((usrInput = stdIn.readLine())!=null){
output.println(usrInput);
System.out.println(“echo: ” + input.readLine());
}
output.close();
input.close();
stdIn.close();
link.close();
}
}
import java.net.*;
import java.io.*;
public class EchoServer{
public static void main(String[] args) throws IOException{
ServerSocket serverSock = null;
try{
serverSock = new ServerSocket(50000);
}
catch (IOException ie){
System.out.println(“Can’t listen on 50000”);
System.exit(1);
}
Socket link = null;
System.out.println(“Listening for connection …”);
try {
link = serverSock.accept();
}
catch (IOException ie){
System.out.println(“Accept failed”);
System.exit(1);
}
System.out.println(“Connection successful”);
System.out.println(“Listening for input …”);
PrintWriter output = new PrintWriter(link.getOutputStream(),
true);
BufferedReader input = new BufferedReader(new
InputStreamReader(link.getInputStream()));
String inputLine;
while ((inputLine = input.readLine())!=null){
System.out.println(“Server: ” + inputLine);
output.println(inputLine);
if(inputLine.equals(“Bye”)){
break;
}
}
output.close();
input.close();
link.close();
serverSock.close();
}
}