def peer_response(self, key, ticket, peer_username):
# Step 1: Decrypt and split the ticket to get the information of the client
ret = False
ticket = CryptoLib.decryptUsingSymetricKey(key, self.sessionID, ticket)
ticket = ticket.split(":")
peer_address = ticket[0]
peer_public_key = ticket[1]
peer = Peer.Peer(peer_username, peer_address, peer_public_key)
# Step 2: Generate and send contribution
b = CryptoLib.generatePublicPrivateKeys(32)
msg = pow(2, b, self.peerPrime)
msg = CryptoLib.encryptUsingPublicKey(peer_public_key, msg)
if not self.send_message(msg, peer_address[0], peer_address[1]):
return ret
# Step 3: Recieve peer contribution and iv and unpack it
peer_contribution = self.receive_response()
peer_contribution = CryptoLib.decryptUsingPrivateKey(self.clientPrivateKey, peer_contribution)
peer_contribution = peer_contribution.split(":")
peer_session_id = peer_contribution[1]
peer_contribution = peer_contribution[0]
# Construct shared key
shared_key = pow(peer_contribution, b, self.peerPrime)
# Step 4: Challenge Response (Two way authentication) - user sends challenge, client increments and sends
# back response which is again incremented and sent back to user. All of this is done using the symmetric
# key encryption with the shared key.
challenge = random.randrange(1, 100000)
challenge = CryptoLib.encyptUsingSymmetricKey(shared_key, peer_session_id, challenge)
if not self.send_message(challenge, peer_address[0], peer_address[1]):
return ret
response = self.receive_response()
response = CryptoLib.decryptUsingSymetricKey(shared_key, peer_session_id, response)
# If authentication is successful, add the peer to list of connected peers and send back response
if response == challenge + 1:
response += 1
response = CryptoLib.encyptUsingSymmetricKey(shared_key, peer_session_id, response)
if not self.send_message(response, peer_address[0], peer_address[1]):
return ret
peer.set_initialization_vector(peer_session_id)
peer.set_shared_key(shared_key)
self.peers[peer_address] = peer
return True
return False
def receiveClientMessages(self):
msg, addr = self.sock.recvfrom(ChatServer.MSG_LEN)
isClientKnown = self.clients.has_key(addr)
if(isClientKnown):
client = self.clients.get(addr)
if(client == None):
print "couldn't retrieve client"
return
if client.get_session_key() is None and client.get_initialization_vector() is None:
decrypted_msg = CryptoLib.decryptUsingPrivateKey(self.private_key, msg)
else:
decrypted_msg = CryptoLib.decryptUsingSymetricKey(client.get_session_key(),
client.get_initialization_vector(), msg)
self.handleClientMessages(decrypted_msg, client, addr)
else:
if self.DBG: print "it's a potential client!!"
self.handleClientMessages(msg, None, addr)
