Asynchrone mixted cryptography built on RSA, AES, SHA-265 and JSON

secure.py

from Crypto.Cipher import AES
from Crypto.Cipher import PKCS1_OAEP
from Crypto.PublicKey import RSA
from Crypto import Random
from hashlib import sha256
import base64
import json

class async():
    def crypt(self, content, crypt_key, sign_key):
        """ Return an all-in-one json message with:
        - "message" the content AES-encrypted with a generated random key
        - "key" the AES random key RSA-encrypted with the recipient's public key
        - "sign" the hash of the content RSA-encrypted with the sender's private key (in fact decrypted)
        """
        aes_key = Random.new().read(32)
        cipher_aes = AES.new(aes_key, 3, "shitty vector 32")
        cipher_rsa = PKCS1_OAEP.new(crypt_key)
        
        message = {}
        message["content"] = base64.b85encode(cipher_aes.encrypt(content.encode())).decode()
        message["key"] = base64.b85encode(cipher_rsa.encrypt(aes_key)).decode()
        message["sign"] = base64.b85encode(sign_key.decrypt(sha256(content.encode()).digest())).decode()
        
        return json.dumps(message, indent=2)

    def decrypt(self, json_str, decrypt_key, sign_key):
        """ Return the clear message and check if it has been send correctly"""
        
        cipher_rsa = PKCS1_OAEP.new(decrypt_key)
        
        data = json.loads(json_str)
        aes_key = cipher_rsa.decrypt(base64.b85decode(data["key"].encode()))
        cipher_aes = AES.new(aes_key, 3, "shitty vector 32")
        content = cipher_aes.decrypt(base64.b85decode(data["content"].encode()))
        
        if sign_key.encode(base64.b85decode(message["sign"])) == sha256(content).digest():
            return content.decode("UTF-8")
        else:
            raise ValueError("Wrong hash")

if __name__ == "__main__":
    asc = async()
    bob = RSA.generate(1024) # Sender's key
    alice = RSA.generate(1024) # Recipient's key
    
    # Bob wants to send a message to Alice
    # Ask the user to write a message then use Alice's public key (to crypt the message) and Bob's Private Key (to sign the message)
    crypted = asc.crypt(input("Message: "), alice.publickey(), bob)
    print("Sending: " + crypted)
    
    # Alice reviece the message from Bob
    # Decrypt the message using Alice's public key and verify ths signature using Bob's pûblic key
    uncrypted = asc.decrypt(crypted, alice, bob.publickey())
    print("Decrypt: " + uncrypted)