Use python to Implement an encryption and decryption program to the web chat script

Use the AES encryption method

import socket import select import sys from thread import *

"""The first argument AF_INET is the address domain of the socket. This is used when we have an Internet Domain with any two hosts The second argument is the type of socket. SOCK_STREAM means that data or characters are read in a continuous flow.""" server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)

# checks whether sufficient arguments have been provided if len(sys.argv) != 3: print "Correct usage: script, IP address, port number" exit()

# takes the first argument from command prompt as IP address IP_address = str(sys.argv[1])

# takes second argument from command prompt as port number Port = int(sys.argv[2])

""" binds the server to an entered IP address and at the specified port number. The client must be aware of these parameters """ server.bind((IP_address, Port))

""" listens for 100 active connections. This number can be increased as per convenience. """ server.listen(100)

list_of_clients = []

def clientthread(conn, addr):

# sends a message to the client whose user object is conn conn.send("Welcome to this chatroom!")

while True: try: message = conn.recv(2048) if message:

"""prints the message and address of the user who just sent the message on the server terminal""" print "<" + addr[0] + "> " + message

# Calls broadcast function to send message to all message_to_send = "<" + addr[0] + "> " + message broadcast(message_to_send, conn)

else: """message may have no content if the connection is broken, in this case we remove the connection""" remove(conn)

except: continue

"""Using the below function, we broadcast the message to all clients who's object is not the same as the one sending the message """ def broadcast(message, connection): for clients in list_of_clients: if clients!=connection: try: clients.send(message) except: clients.close()

# if the link is broken, we remove the client remove(clients)

"""The following function simply removes the object from the list that was created at the beginning of the program""" def remove(connection): if connection in list_of_clients: list_of_clients.remove(connection)

while True:

"""Accepts a connection request and stores two parameters, conn which is a socket object for that user, and addr which contains the IP address of the client that just connected""" conn, addr = server.accept()

"""Maintains a list of clients for ease of broadcasting a message to all available people in the chatroom""" list_of_clients.append(conn)

# prints the address of the user that just connected print addr[0] + " connected"

# creates and individual thread for every user # that connects start_new_thread(clientthread,(conn,addr))

conn.close() server.close()

==============================================================================

[2] Save this file as client.py. This is the client side script, that each user must use in order to connect to the server.

import socket import select import sys

server = socket.socket(socket.AF_INET, socket.SOCK_STREAM) if len(sys.argv) != 3: print "Correct usage: script, IP address, port number" exit() IP_address = str(sys.argv[1]) Port = int(sys.argv[2]) server.connect((IP_address, Port))

while True:

# maintains a list of possible input streams sockets_list = [sys.stdin, server]

""" There are two possible input situations. Either the user wants to give manual input to send to other people, or the server is sending a message to be printed on the screen. Select returns from sockets_list, the stream that is reader for input. So for example, if the server wants to send a message, then the if condition will hold true below.If the user wants to send a message, the else condition will evaluate as true""" read_sockets,write_socket, error_socket = select.select(sockets_list,[],[])

for socks in read_sockets: if socks == server: message = socks.recv(2048) print message else: message = sys.stdin.readline() server.send(message) sys.stdout.write("") sys.stdout.write(message) sys.stdout.flush() server.close()

============================================================================== [3]. HOW TO RUN OR INITIATE THE CHAT

/* Both the server and client script can then be run from the Command prompt (in Windows) or from bash Terminal (Linux users) by simply typing

"python chat_server.py " or "python client.py ".

For example, */

python chat_server.py 192.168.55.13 8081

python client.py 192.168.55.13 8081