Implementing-cryptography-using-python

248 Chapter 9 ■ Mastering Cryptography Using Python
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Encrypt the message using ECC
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Implement the Elliptic Curve Diffie-Hellman exchange
Constructing a Plaintext Communications Application
Our first task is to revisit the construction of a threaded server with unencrypted
traffic, which was introduced in Chapter 7. In addition to building a server and
client Python file, we will create a helper file here that will support the coding
additions we will implement as we are building our Python solution.
The architecture for the application includes a server file (crypto _ server _ a.
py), a client file (crypto _ client _ a.py), and a helper file that will be used by
both the client and server since they share many of the same components. One
side encrypts, and the other one decrypts. For the sake of keeping this example
simple, we will only do one-way communication. The same techniques used in
this chapter can be used between any applications that transmit data over UDP.
Creating a Server
Our first step is to create an application that will use UDP sockets to accept
packets from other programs. For our example we can use the localhost so that
you can use the client application to send plaintext messages to the server. The
server will then display the text as received.
Here’s the Python code:
# Message Receiver - crypto_chat_server.py
import hashlib, random, os, time
from binascii import hexlify
from socket import *
import Chapter9.ch9_crypto_chat as ct
def get_dh_sharedsecret():
return
def get_dh_sharedkey():
return
def decrypt(ciphertext, usePKI, useDH, serverSecret):
#msg = ct.decrypt(ciphertext, usePKI, useDH, serverSecret)
try:
msg = ct.decrypt(ciphertext, usePKI, useDH, serverSecret)
except:
msg = ciphertext
return msg