Implementing-cryptography-using-python

Chapter 6 ■ Using Cryptography with Images 177
Next, we will load a file with plaintext data and then encrypt the data using
the encrypt() method. The file is then saved to storage:
filename = “sometextfile.txt”
f = Fernet(key)
with open(filename, "rb") as file:
# read all file data
file_data = file.read()
# encrypt data
encrypted_data = f.encrypt(file_data)
# write the encrypted file
with open(filename, "wb") as file:
file.write(encrypted_data)
The decryption process is almost identical, but we use the decrypt() function
of the Fernet object:
$filename = “sometextfile.txt”
f = Fernet(key)
with open(filename, "rb") as file:
# read the encrypted data
encrypted_data = file.read()
# decrypt data
decrypted_data = f.decrypt(encrypted_data)
# write the original file
with open(filename, "wb") as file:
file.write(decrypted_data)
Now that you have the concepts, you can wrap all these snippets up into
something a little more flexible. The following Python code accepts a key, a file,
and either a decryption or encryption flag:
from cryptography.fernet import Fernet
import os
def write_key():
# Generates a key and save it into a file
key = Fernet.generate_key()
with open("ch6.key", "wb") as key_file:
key_file.write(key)
def load_key():
#Loads the key from the current directory named 'ch6.key'
return open("ch6.key", "rb").read()
def encrypt(filename, key):
# encrypts the file and writes it using filename and key
f = Fernet(key)
with open(filename, "rb") as file:
# read all file data