Implementing-cryptography-using-python

Chapter 9 ■ Mastering Cryptography Using Python 265
def get_dh_sharedkey():
key = int(open('server_public_dh_key.pem').read())
clientDH.generateSharedKey(key)
clientDH.getSharedKey()
clientDH.generateSharedKey(key)
private_key = clientDH.key
return private_key
As with the server file, the client file needs to address the results determined
by the message sent over UDP:
# determine if the user initiated a special command
result = ct.check_client_command(data)
# handle any custom commands
if data == b'exit':
break
if result == 0:
break
if result == 10:
sendUsingPrivate = False;
if result == 11:
sendUsingPrivate = True;
skipEncryption = True;
if result == 20:
sendUsingDH = False;
if result == 21:
sendUsingDH = True;
skipEncryption = True;
Prior to going into the loop, you will need to get the client secret by calling
the get _ dh _ sharedkey() method:
# no matter what, get the ECC shared key, only use it if the user
enables
clientSecret = get_dh_sharedkey()
print ("Welcome to Crypto-Chat! \n")
print (" Enable PKI: type 'addPKI'")
print (" Disable PKI: type 'removePKI'")
print (" Enable Diffie-Hellman: type 'addDH'")
print (" Disable Diffie-Hellman: type 'removeDH'")
print ()
We also make a number of changes to the client screen to show the user the
special commands. These are nothing more than just print() calls. The final
version should look similar to Figure 9.8.