Implementing-cryptography-using-python

Chapter 6 ■ Using Cryptography with Images 181
with the same encryption key. The decryption process is the reverse. When
using the ECB mode process, identical blocks of plaintext will be encrypted
the same and will yield identical blocks of ciphertext or an encrypted image.
While the weaknesses of the cipher mode may not be initially apparent, when
we examine the mode in image cryptography, a major security vulnerability
appears. In Figure 6.6, you will see the difference between the ECB mode
versus the other modes that are available.
Figure 6.6: Image encryption modes
Exploring a Simple ECB Mode Example
For our first example, we will examine how to produce the ECB mode encrypted
image. First, we start out with a bitmap file that has a distinct pattern, as shown
in Figure 6.7.
Figure 6.7: Plane image in BMP format
The first step is to import the library and set a key. For this example, we will
use a 16-byte key, although 24-byte and 32-byte keys are supported:
>>> from Crypto.Cipher import AES
>>> key = b"aaaabbbbccccdddd"
>>> cipher = AES.new(key, AES.MODE_ECB)