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Practical - 8
Q-1 Show a píactical scenaíio of Key Distíibution. Use the sepaíate key-shaíing seíveí that shaíes
the secíet key cíeated using the AES-256-bit algoíithm and shaíe the secíet key using the RSA
algoíithm with 2048 bits key size. ľhe key-shaíing seíveí píoduces a new secíet key foí each new
communication between two nodes.
Code: from Crypto.Cipher import AES, PKCS1_OAEP
from Crypto.PublicKey import RSA from
Crypto.Random import get_random_bytes
import hashlib
class KeySharingServer:
def init (self):
self.private_key = RSA.generate(2048) self.public_key
= self.private_key.publickey()
def generate_session_key(self):
return get_random_bytes(32) # AES-256 bit key size
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def encrypt_session_key(self, session_key,
recipient_public_key):
cipher_rsa = PKCS1_OAEP.new(recipient_public_key)
encrypted_session_key = cipher_rsa.encrypt(session_key)
return encrypted_session_key
def decrypt_session_key(self, encrypted_session_key):
cipher_rsa = PKCS1_OAEP.new(self.private_key)
session_key = cipher_rsa.decrypt(encrypted_session_key)
return session_key
class Node:
def init (self, name, key_sharing_server): self.name
= name
self.key_sharing_server = key_sharing_server
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self.session_key = None
def receive_session_key(self, encrypted_session_key):
decrypted_session_key =
self.key_sharing_server.decrypt_session_key(encrypted_session_key)
self.session_key = decrypted_session_key
def encrypt_message(self, message):
cipher_aes = AES.new(self.session_key, AES.MODE_EAX)
ciphertext, tag =
cipher_aes.encrypt_and_digest(message.encode('utf-8'))
return ciphertext, cipher_aes.nonce, tag
def decrypt_message(self, ciphertext, nonce, tag):
cipher_aes = AES.new(self.session_key, AES.MODE_EAX,
nonce=nonce) decrypted_message
=
cipher_aes.decrypt_and_verify(ciphertext, tag)
return decrypted_message.decode('utf-8')
# Scenario setup key_sharing_server =
KeySharingServer() alice = Node("Alice",
key_sharing_server) bob = Node("Bob",
key_sharing_server)
# Key sharing session_key =
key_sharing_server.generate_session_key()
encrypted_session_key_for_alice =
key_sharing_server.encrypt_session_key(session_key,
alice.key_sharing_server.public_key)
encrypted_session_key_for_bob =
key_sharing_server.encrypt_session_key(session_key,
bob.key_sharing_server.public_key)
alice.receive_session_key(encrypted_session_key_for_alice)
bob.receive_session_key(encrypted_session_key_for_bob)
# Communication message_to_bob = "Hello Bob,
this is Alice!"
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ciphertext, nonce, tag = alice.encrypt_message(message_to_bob)
decrypted_message = bob.decrypt_message(ciphertext, nonce, tag)
print(f"Alice sent to Bob: {message_to_bob}") print(f"Bob
received from Alice: {decrypted_message}")
Output:
