Implement DH Key exchange algorithm for the simple client-server communication a

Question

Implement DH Key exchange algorithm for the simple client-server communication as implemented in the provided files server.py & client.py. The current code demonstrates the sending of a file from the server to the client and sets up the appropriate socket connections. The students will NOT need to create the connections, they cam piggy back on the connections created and achieve the public key exchange for DH algorithm. Once the shared key has been established the students should encrypt the file being transferred from the server to the client and transfer the encrypted file. On the client side the file should be decrypted using the same shared key. Finally the server should also send the hash of the encrypted file and the client should verify that it received the same file by hash comparison. Note that Python provides functions to compute the hash of inputs. The students should use a variation of the SHA or MD5 hash as implemented in Python.

Client PY:

Server PY:

Explanation / Answer

I have modified your code to fullfill all the above mentioned requrements.

1. Securly send encryption and decryption key using DH_Algorithim

2. Encryption and Decrytion of file.

3. Hashing of file data to match the content

I have commented all the modified code with Modified comment.

Server.py

'''

File transfer server code. Not multi-threaded.

'''

import socket # Import socket module

import struct

from Crypto.Cipher import DES

import hashlib

# Reserve a port for your service (*client must connect with this port number)

port = 63000

s = socket.socket() # Create a socket object

host = socket.gethostname() # Get local machine name

s.bind((host, port)) # Bind to the port

s.listen(5) # Now wait for client connection and listen for requests

def serve():

"""

The server code. Accepts connections from clients and transfers a file.

The file should be in the same directory. Ensure that there is only

one client connecting. This is not multi-threaded at this point.

"""

# ----------Modified-------------------------------------

# Creating public modulous known to client and server

p = 23

# Creating secret key known to server only

secret_key = 3

# Creating public base known to client and server

g = 5

# Getting the key which server will share with client

sharing_key = (g ** secret_key) % p

# ----------------------------------------------------------

print('Server listening....')

while True:

conn, addr = s.accept() # Establish connection with client, returns a tuple

print('Got connection from', addr)

data = conn.recv(1024)

# ----------Modified------------------------------------

# Server will send its sharing key to server

conn.send(bytes(str(sharing_key) + '', encoding='UTF8'))

# Server will recieve key from server

recieved_key = int(conn.recv(1024))

# Server will generate a common key using its secret key and public modulous

common_key = (recieved_key ** secret_key) % p

print('CommonKey:', common_key)

# Creating object for encrypting file

# Common key with a random string is used to generate a

# strong password

obj = DES.new(str(common_key) + "123456",

DES.MODE_CFB, "12345678")

# ----------------------------------------------------

print('Server received', repr(data))

# file to transfer

filename = './sample.txt'

f = open(filename, 'rb')

l = f.read(1024)

while (l):

# ----------Modified------------------------------------

# Genrating hash of file

hashobj = hashlib.md5(l)

# Server will send encrpted file to client

conn.send(obj.encrypt(l))

# Server will send hash of file to client

conn.send(bytes(str(hashobj.hexdigest()), encoding='UTF8'))

# ----------------------------------------------------

print('Sent ', repr(l))

l = f.read(1024)

f.close()

print('Done sending')

conn.send(bytes('File transfer complete!', encoding='UTF8'))

conn.close()

if __name__ == '__main__':

serve()

  

Client.py

import socket

import struct

from Crypto.Cipher import DES

import hashlib

def client():

"""

Client code for connecting to server and receiving file from server.

Right now we assume both work on localhost.

"""

s = socket.socket() # Create a socket object

host = socket.gethostname() # Get local machine name

port = 63000 # Make sure that client pings server on correct port

# ----------Modified------------------------------------

# Creating public modulous known to client and server

p = 23

# Creating secret key known to client only

secret_key = 4

# Creating public base known to client and server

g = 5

# Getting the key which client will share with server

sharing_key = (g ** secret_key) % p

# ----------------------------------------------------

s.connect((host, port)) # connect with the server

# communicate with the server

s.send(bytes("Hello server!", encoding='UTF8'))

# ----------Modified------------------------------------

# Client will recieve key from server

recieved_key = int(s.recv(1024))

# Client will generate a common key using its secret key and public modulous

common_key = (recieved_key ** secret_key) % p

print('CommonKey:', common_key)

# Client will send its sharing key to server

s.send(bytes(str(sharing_key) + '', encoding='UTF8'))

# Creating object for decrypting file using

# Common key with a random string is used to generate a

# strong password

obj = DES.new(str(common_key) + "123456",

DES.MODE_CFB, "12345678")

# ----------------------------------------------------

with open('./client.txt', 'wb') as f:

while True:

print('Receiving data...')

# ----------Modified------------------------------------

# Client will recieve the encrypted file data

data = s.recv(1024)

# Client will recieve the hash of file

recieved_hash = s.recv(4096)

# Client will decrypt the data and hash it

data_hash = hashlib.md5(obj.decrypt(data)).hexdigest()

# ----------------------------------------------------

if not data:

break

# ----------Modified------------------------------------

# Client will match recieved hash and generated hash

# If both hashes match, data will be saved to file.

if (data_hash == str(recieved_hash, encoding='UTF8')):

# Client will

print('Mathing hash successfully.')

# write data to a file

f.write(obj.decrypt(data))

else:

print('Error: Mathing hashes')

# ----------------------------------------------------

f.close()

print('Successfully obtained file from server')

s.close()

print('Connection closed')

if __name__ == '__main__':

client()

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