Implementing-cryptography-using-python

176 Chapter 6 ■ Using Cryptography with Images
File Cryptography Using Fernet
In this section, we will explore image cryptography using Fernet, which is an
implementation of symmetric authenticated cryptography. Symmetric encryption,
which you may remember is synonymous for “same key,” means that we
use the same key to both encrypt and decrypt. You will begin by generating
a key and then saving it to a file. The generate_key() function will generate a
new Fernet key each time it is called; if you lose this key, you will not be able
to decrypt any data that you encrypted with this key. Therefore, once the key
gets generated, you will save it to disk. Each time you have the system generate
a key for you, you should save it; the alternative is to create your own key.
The Python code to generate the key and store it looks like the following:
key = Fernet.generate_key()
with open("ch6.key", "wb") as key_file:
key_file.write(key)
To load the key file once it is stored, you can use the following Python code:
return open("ch6.key", "rb").read()
Once you have an encryption system and a key, you should be ready to
encrypt your message. Do not forget to encode your message; this will convert
the string to bytes suitable for encrypting. Your message assignment should
look like the following:
plaintext = "I have a secret I want to share but only if you have the
key.".encode()
From here, we are ready to start our encryption process:
f = Fernet(key)
ciphertext = f.encrypt(plaintext)
print (ciphertext)
Assuming you are playing along, you should have something similar to
Figure 6.5.
Figure 6.5: Python output for Fernet