Python 'bytes' object has no attribute 'decrypt'

I'm trying some encryption examples.

and i keep get

dec_msg = dec_key.decrypt(enc_msg)

AttributeError: 'bytes' object has no attribute 'decrypt'

this error.

from cryptography.fernet import Fernet
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.asymmetric import rsa,padding
from cryptography.hazmat.primitives import serialization,hashes

key = Fernet.generate_key()
f_object = Fernet(key)

# encrypt plain_data with AES
plain_data = bytes(input(), encoding='utf8')
enc_msg = f_object.encrypt(plain_data)

# Get public / private key
with open("public_key.pem", "rb") as key_file:
     public_key = serialization.load_pem_public_key(key_file.read(),backend=default_backend())
with open("private_key.pem", "rb") as key_file:
     private_key = serialization.load_pem_private_key(key_file.read(),password=None,backend=default_backend())

# encrypt symmetric key and decrypt encrypted symmetric key
enc_key = public_key.encrypt(plain_data, padding.OAEP(mgf=padding.MGF1(algorithm=hashes.SHA256()), algorithm=hashes.SHA256(), label=None))
print("enc_key and enc_message send through insecure channel.")
dec_key = private_key.decrypt(enc_key,padding.OAEP(mgf=padding.MGF1(algorithm=hashes.SHA256()), algorithm=hashes.SHA256(), label=None))

# decrypt AES encrypted message using decrypted symmetric key
dec_key.decode('utf-8')
dec_msg = dec_key.decrypt(enc_msg)

# print result
print(dec_msg)

I tried to decode my dec_key but it doesnt work.

Is there any more thing to decode? I don't see them.

It looks like there are two problems:

1. When you create enc_key, you're providing plain_data as input instead of key.

2. dec_key is an instance of bytes and should be used to create another Fernet instance.

Here's your example modified to address those issues:

from cryptography.fernet import Fernet
from cryptography.hazmat.primitives.asymmetric import rsa,padding
from cryptography.hazmat.primitives import serialization,hashes

key = Fernet.generate_key()
f_enc = Fernet(key)

# encrypt plain_data with AES
print("input message to be encrypted: ", end="")
plain_data = bytes(input(), encoding='utf8')
enc_msg = f_enc.encrypt(plain_data)

# Get public / private key
with open("public_key.pem", "rb") as key_file:
    public_key = serialization.load_pem_public_key(key_file.read())
with open("private_key.pem", "rb") as key_file:
    private_key = serialization.load_pem_private_key(
        key_file.read(), password=None)

# encrypt symmetric key
enc_key = public_key.encrypt(
    key,
    padding.OAEP(mgf=padding.MGF1(algorithm=hashes.SHA256()),
    algorithm=hashes.SHA256(),
    label=None)
)

print("send enc_key and enc_msg through an insecure channel...")

# decrypt symmetric key
dec_key = private_key.decrypt(
    enc_key,
    padding.OAEP(mgf=padding.MGF1(algorithm=hashes.SHA256()),
    algorithm=hashes.SHA256(),
    label=None)
)

# decrypt encrypted message using decrypted symmetric key
f_dec = Fernet(dec_key)
dec_msg = f_dec.decrypt(enc_msg)

# print result
print("decrypted message: " + dec_msg.decode('utf-8'))

Output:

$ python3 example.py
input message to be encrypted: this is a test
send enc_key and enc_msg through an insecure channel...
decrypted message: this is a test