Implementing-cryptography-using-python

Chapter 7 ■ Message Integrity 221
f = Fernet(key)
def encrypt(plaintext):
h = hashlib.md5(plaintext).hexdigest()
print("Message hash: " + h)
mmac = str(str(plaintext,'utf-8') + h).encode()
msg = f.encrypt(mmac)
return msg
while True:
data = str(input("Enter message to send or type 'exit': ")).encode()
ciphertext = encrypt(data)
UDPSock.sendto(ciphertext, addr)
if data == b'exit':
break
if data == b'newkey':
key = input("Enter the secret key: ")
f = Fernet(key)
UDPSock.close()
os._exit(0)
The preceding code sample will generate the message digest and send it to
the server so that the server can determine if the received message has been
tampered with. Your result should appear similar to Figure 7.9.
Figure 7.9: Message and MAC client
Summary
In this chapter, we continued our exploration of hashing algorithms using
Python. Hopefully, you understand how to effectively use message digests to
protect the integrity of your messages. Algorithms such as SHA1 and MD5 have
proven to be victims of birthday attacks and the length extension attack. One