Assuming there is one client, and one server:

$1.$ The client acts as the sender$,$ encrypting and encoding the message before sending it$.$

$2.$ The client then transmits the encrypted$/$encoded data to the server. We also assume that the

client and the server had shared the same key $"$CS$645$@CS $-$spring".

$3.$ Finally, when the server receives the message, it appears as

"YidDZHVvQlBURXJNSWVUL$0$pUK$0$dEelVJb$3$VVUEhhdm$9$xalVUUmZQSzUvZUpua$1$BvZVFuU$2$tBL$0$dndFFNWWZOZm$9$TJw$==".$

Please assist the server in recovering the original message. I have already provided the code.

Please fill in the missing content and run it using Python.

from cryptography.hazmat.primitives import padding

from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes

from cryptography.hazmat.backends import default$\_$backend

import os

import base$64$

def encrypt$\_$message$($key$,$ message$)$:

iv $=$ os$.$urandom$(16)$ # Generate a random IV

padder $=$ padding.PKCS$7(128).$padder$()$

padded$\_$data $=$ padder.update$($message$.$encode$())+$ padder.finalize$()$

cipher $=$ Cipher$($algorithms$.$AES$($key$),$ modes.CBC$($iv$),$ backend$=$default$\_$backend$())$

encryptor $=$ cipher.encryptor$()$

ciphertext $=$ encryptor.update$($padded$\_$data$)+$ encryptor.finalize$()$

return base$64.$b$64$encode$($iv $+$ ciphertext$)$

def decrypt$\_$message$($key$,$ ciphertext$)$:

data $=$ base$64.$b$64$decode$($ciphertext$)$

iv $=$ data$[$:$16]$

ciphertext $=$ data$[16$:$]$

cipher $=$ Cipher$($algorithms$.$AES$($key$),$ modes.CBC$($iv$),$ backend$=$default$\_$backend$())$

decryptor $=$ cipher.decryptor$()$

padded$\_$data $=$ decryptor.update$($ciphertext$)+$ decryptor.finalize$()$

unpadder $=$ padding.PKCS$7(128).$unpadder$()$

message $=$ unpadder.update$($padded$\_$data$)+$ unpadder.finalize$()$

return message.decode$()$

# Decrypt the message

decrypted$\_$message $=$ decrypt$\_$message$($key$,$ encrypted$\_$message$)$

print$("$Decrypted:$",$ decrypted$\_$message$)$