I recognize the importance of properly implement cryptographic functions. Since this is my first time using them I really wanted a second opinion on my method. Therefore, I was wondering if my method of sign-then-encrypt as implemented would be a valid method of safely achieving those results.

import rsa import textwrap  def gen_keys(size):     print('Generating new keys...')     pubkey, privkey = rsa.newkeys(size, poolsize=8)     print('Keys generated!')     return pubkey, privkey   def encrypt_full_message(message, _pubkey, privkey):     parts = textwrap.wrap(message, max)     message_to_send = b''     for part in parts:         part = part.encode('utf-8')         signature = rsa.sign(part, privkey, 'SHA-256')         encrypted_message = rsa.encrypt(part, _pubkey)         print(len(signature), len(encrypted_message))         message_to_send += encrypted_message         message_to_send += signature     return message_to_send  def decrypt_full_message(message, privkey, _pubkey):     parts = [message[i:i+256] for i in range(0, len(message), 256)]     messages = parts[::2]     signatures = parts[1::2]     fmessage = b''     for signature in signatures:         for message in messages:             message = rsa.decrypt(message, privkey)             if rsa.verify(message, signature, _pubkey):                 fmessage += message             else:                 print('Message has been tampered with.')     return message