対処方法：a bytes-like object is required, not 'NoneType'

Question

###前提・実現したいこと
ボットネット間の通信をAESで暗号化したいのですが
a bytes-like object is required, not 'NoneType'
のエラーメッセージが出て困っています。

###発生している問題・エラーメッセージ

a bytes-like object is required, not 'NoneType'

###該当のソースコード

import struct

from Crypto import Random
from Crypto.Cipher import AES
from Crypto.Hash import HMAC, SHA256
from lib.padding import pad, unpad


from dh import create_dh_key, calculate_dh_secret

class StealthConn(object):
    
    
    def __init__(self, conn, client=False, server=False, verbose=False):
        self.conn = conn
        self.cipher = None
        self.client = client
        self.server = server
        self.verbose = verbose
        self.initiate_session()
        self.secret_key = None
        self.block_size = 32

    def initiate_session(self):
        # Perform the initial connection handshake for agreeing on a shared secret 
        ### TODO: Your code here!
        # This can be broken into code run just on the server or just on the client
        if self.server or self.client:
            my_public_key, my_private_key = create_dh_key()
            # Send them our public key
            self.send(bytes(str(my_public_key), "ascii"))
            # Receive their public key
            their_public_key = int(self.recv())
            # Obtain our shared secret
            shared_hash = calculate_dh_secret(their_public_key, my_private_key)
            print("Shared hash: {}".format(shared_hash))

       
        
        self.secret_key = bytes(str(shared_hash[:16]), "ascii")
        iv = Random.new().read(AES.block_size)
        self.cipher = AES.new(self.secret_key, AES.MODE_CBC, iv)
        print('secret key : ', self.secret_key)
            
    
    def send(self, data):
        print('send')
        
        if self.cipher is not None:
            iv = Random.new().read(AES.block_size)
            cipher = AES.new(self.secret_key, AES.MODE_CBC, iv)

            #上のself.secret_keyがnoneになっているみたいです
            pad_data = pad(data, self.block_size, style='pkcs7')
            
            h = HMAC.new(bytes(str(self.secret_key), "ascii"), digestmod=SHA256)
            h.update(pad_data)
            hmac = bytes(h.hexdigest(), "ascii")
            
            data_pad_hmac = pad_data + hmac
            
            encrypted_data = self.cipher.encrypt(data_pad_hmac)
    
            if self.verbose:
                print("Original data: {}".format(data))
                print("Encrypted data: {}".format(repr(encrypted_data)))
                print("Sending packet of length {}".format(len(encrypted_data)))
        else:
            encrypted_data = data

        # Encode the data's length into an unsigned two byte int ('H')
        pkt_len = struct.pack('H', len(encrypted_data))
        self.conn.sendall(pkt_len)
        self.conn.sendall(encrypted_data)

    def recv(self):
        print('recv')
        # Decode the data's length from an unsigned two byte int ('H')
        pkt_len_packed = self.conn.recv(struct.calcsize('H'))
        unpacked_contents = struct.unpack('H', pkt_len_packed)
        pkt_len = unpacked_contents[0]
        
        encrypted_data = self.conn.recv(pkt_len)
        
        if self.cipher is not None:
            iv = Random.new().read(AES.block_size)
            cipher = AES.new(self.secret_key, AES.MODE_CBC, iv)
            print('secret key : ', self.secret_key)
            
            data = self.cipher.decrypt(encrypted_data)
            
            hmac = data[len(encrypted_data)-64:]
            pad_data = data[:64]
            h = HMAC.new(bytes(str(self.secret_key), "ascii"), digestmod=SHA256)
            h.update(pad_data)
            
            verify = bytes(h.hexdigest(), "ascii")
            print('verify : ', verify)
            
            
            #data = unpad(pad_data, self.block_size, style='pkcs7')
            
            if hmac == verify:
                if self.verbose:
                    print("Receiving packet of length {}".format(pkt_len))
                    print("Encrypted data: {}".format(repr(encrypted_data)))
                    print("Original data: {}".format(data))
            else:
                print("Message is modified")
    
        else:
            data = encrypted_data
        
        

        return data

    def close(self):
        self.conn.close()

###試したこと
initiate_session()の中でsecret_keyを指定しているのですが
recv()とsend()の中ではsecret_key = Noneになっているようです。

###補足情報(言語/FW/ツール等のバージョンなど)
より詳細な情報

Answer 1

ここ逆じゃないですか？

self.initiate_session()
self.secret_key = None