from secrets import token_bytes

def random_key(length):
  key = token_bytes(nbytes=length)
  key_int = int.from_bytes(key, 'big')
  return key_int

def encrypt(raw):
  raw_bytes = raw.encode()
  raw_int = int.from_bytes(raw_bytes, 'big')
  key_int = random_key(len(raw_bytes))
  return raw_int ^ key_int, key_int

def decrypt(encrypted, key_int):
  decrypted = encrypted ^ key_int
  length = (decrypted.bit_length() + 7) // 8
  decrypted_bytes = int.to_bytes(decrypted, length, 'big') 
  return decrypted_bytes.decode()

> raw = '画图省识春风面，环珮空归夜月魂'
> encrypted = encrypt(raw)
> encrypted
(217447100157746604585...,
 9697901906831571319...)
> decrypt(*encrypted)
'画图省识春风面，环珮空归夜月魂'

import json
from pathlib import Path

def encrypt_file(path, key_path=None, *, encoding='utf-8'):
  path = Path(path)
  cwd = path.cwd() / path.name.split('.')[0]
  path_encrypted = cwd / path.name 
  if key_path is None:
    key_path = cwd / 'key'
  if not cwd.exists():
    cwd.mkdir()
    path_encrypted.touch()
    key_path.touch()

  with path.open('rt', encoding=encoding) as f1,     path_encrypted.open('wt', encoding=encoding) as f2,       key_path.open('wt', encoding=encoding) as f3:
    encrypted, key = encrypt(f1.read())
    json.dump(encrypted, f2)
    json.dump(key, f3)

def decrypt_file(path_encrypted, key_path=None, *, encoding='utf-8'):
  path_encrypted = Path(path_encrypted)
  cwd = path_encrypted.cwd()
  path_decrypted = cwd / 'decrypted' 
  if not path_decrypted.exists():
    path_decrypted.mkdir()
    path_decrypted /= path_encrypted.name
    path_decrypted.touch()
  if key_path is None:
    key_path = cwd / 'key'
  with path_encrypted.open('rt', encoding=encoding) as f1,     key_path.open('rt', encoding=encoding) as f2,     path_decrypted.open('wt', encoding=encoding) as f3:
    decrypted = decrypt(json.load(f1), json.load(f2))
    f3.write(decrypted)