Implementing-cryptography-using-python

Chapter 6 ■ Using Cryptography with Images 179
if encrypt_ and decrypt_:
raise TypeError("Please specify whether you want to encrypt the
file or decrypt it.")
elif encrypt_:
encrypt(file, key)
elif decrypt_:
decrypt(file, key)
else:
raise TypeError("Please specify whether you want to encrypt the
file or decrypt it.")
Image Cryptography Using Fernet
Using our previous example, you can now write a solution that will allow you
to specify the original image and change the encrypted file to a specific name;
in this case, the ch6_secret_image.jpg file will be encrypted as e_ch6_secret_
im age.jpg and then immediately decrypted to d_ch6_secret_image.jpg. The
image resolution between the original file and the decrypted file is identical
as the Fernet algorithm operates on the file itself and does not alter the pixels
of the image.
In the following example, I removed the reading and writing key since the
encryption and decryption are happening in the same process. The encryption
process here is not specific to just images and can be used on a variety of data
types. The takeaway from this program should be the full encryption at the file
level and not the pixel level:
def encrypt(filename, newfile, key):
"""
Given a plain image (str), the new file name, and key (bytes), it
encrypts the file and write it
"""
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(newfile, "wb") as file:
file.write(encrypted_data)
def decrypt(filename, newfile, key):
"""
Given a encrypted file (str), the new file name, and key (bytes), it
decrypts the file and write it
"""
f = Fernet(key)