Book Image

Hands-On Cryptography with Python

By : Samuel Bowne
Book Image

Hands-On Cryptography with Python

By: Samuel Bowne

Overview of this book

Cryptography is essential for protecting sensitive information, but it is often performed inadequately or incorrectly. Hands-On Cryptography with Python starts by showing you how to encrypt and evaluate your data. The book will then walk you through various data encryption methods,such as obfuscation, hashing, and strong encryption, and will show how you can attack cryptographic systems. You will learn how to create hashes, crack them, and will understand why they are so different from each other. In the concluding chapters, you will use three NIST-recommended systems: the Advanced Encryption Standard (AES), the Secure Hash Algorithm (SHA), and the Rivest-Shamir-Adleman (RSA). By the end of this book, you will be able to deal with common errors in encryption.
Table of Contents (9 chapters)

ECB and CBC modes

We'll compare Electronic Codebook (ECB) and Cipher Block Chaining (CBCand show you how to implement AES CBC in Python.


In the ECB method, each block of plaintext is encrypted with the key separately, so if you have two blocks of plaintext that are the same, they will result in identical ciphertext:

If you have something like an image here with large areas of solid colors such as gray and black and then you encrypt it, you'll just get different colors but the pattern won't change:

That's not good. You can still see that this is a picture of a penguin, and that's not what most people expect out of encryption. You expect the encryption to conceal the data so attackers looking at the encrypted data can't tell what the message is, and here that property is not present.

Thus, CBC is considered the best solution to this problem.


In addition to the key, you add an initialization vector, which is XOR'd with the plaintext before encryption. Then for the next block, you take the...