Hands-On Cryptography with Python

Leverage the power of Python to encrypt and decrypt data

Samuel Bowne

• Publisher: Packt Publishing
• Year: 2018
• eBook ISBN: 9781789537949
• Edition: 1
• Topic: Informatik
• Subtopic: Kryptographie

Learn to evaluate and compare data encryption methods and attack cryptographic systemsAbout This Book• Explore popular and important cryptographic methods• Compare cryptographic modes and understand their limitations• Learn to perform attacks on cryptographic systemsWho This Book Is ForHands-On Cryptography with Python is for security professionals who want to learn to encrypt and evaluate data, and compare different encryption methods.What You Will Learn• Protect data with encryption and hashing• Explore and compare various encryption methods• Encrypt data using the Caesar Cipher technique• Make hashes and crack them• Learn how to use three NIST-recommended systems: AES, SHA, and RSA• Understand common errors in encryption and exploit themIn DetailCryptography 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.Style and approachA practical guide that will help the readers to encrypt their data with ease

Obfuscation

Python is the best language to start with if you are a beginner, which is what makes it so popular. You can write powerful code with just a few lines, and most importantly, you can handle arbitrarily large integers with complete precision. This book covers essential cryptography concepts; classic encryption methods, such as the Caesar cipher and XOR; the concepts of confusion and diffusion, which determine how strong a crypto system is; hiding data with obfuscation; hashing data for integrity and passwords; and strong encryption methods and attacks against these methods, including the padding oracle attack. You do not need to have programming experience to learn any of this. You don't need any special computer; any computer that can run Python can do these projects. We'll not be inventing new encryption techniques just for learning how to use standard pre-existing ones that don't require anything more than very basic algebra.

We will first deal with obfuscation, the basic idea of what encryption is, and old-fashioned encryption techniques that hide data to make it more difficult to read. This latter process is one of the basic activities that encryption modules use in combination with other methods to make stronger, more modern encryption techniques.

In this chapter, we will cover the following topics:

• About cryptography
• Installing and setting up Python
• Caesar cipher and ROT13
• base64 encoding
• XOR

About cryptography

The term crypto has become overloaded recently with the introduction of all currencies, such as Bitcoin, Ethereum, and Litecoin. When we refer to crypto as a form of protection, we are referring to the concept of cryptography applied to communication links, storage devices, software, and messages used in a system. Cryptography has a long and important history in protecting critical systems and sensitive information.

During World War II, the Germans used Enigma machines to encrypt communications, and the Allies went to great lengths to crack the encryption. Enigma machines used a series of rotors that transformed plaintext to ciphertext, and by understanding the position of the rotors, the Allies were able to decrypt the ciphertext into plaintext. This was a momentous achievement but took significant manpower and resources. Today it is still possible to crack certain encryption techniques; however, it is often more feasible to attack other aspects of cryptographic systems, such as the protocols, the integration points, or even the libraries used to implement cryptography.

Cryptography has a rich history; however, nowadays, you will come across new concepts, such as blockchain, that can be used as a tool to help secure the IoT. Blockchain is based on a set of well-known cryptographic primitives. Other new directions in cryptography include quantum-resistant algorithms, which hold up against a theorized onslaught of quantum computers and quantum key distributions. They use protocols such as BB84 and BB92 to leverage the concepts of quantum entanglement and create good-quality keys for using classical encryption algorithms.

Installing and setting up Python

Python has never been easy to install. In order to proceed, let's make sure that we have set up Python on our machine. We will see how to use Python on macOS or Linux and how to install it on Windows.

Using Python on Mac or Linux

On a macOS or Linux system, you do not need to install Python because it is already included. You just need to open a Terminal window and enter the python command. This will put you in an interactive mode where you can execute python commands one by one. You can close the interactive mode by executing the exit() command. So, basically, to create a script, we use the nano text editor followed by the name of the file. We then enter python commands and save the file. You can then run the script with python followed by the script name. So, let's see how to use Python on macOS or Linux in the following steps:

1. Open the Terminal on a macOS or Linux system and run the python command. This opens an interactive mode of Python, as shown in the following screenshot:

2. When you use the print command, it prints Hello right away:

>>> print "Hello"
Hello

3. We will then leave with the following command:

>>> exit()

4. As mentioned before, to use Python in interactive mode, we will enter the command as shown:

$ nano hello.py

5. In the hello.py file, we can write commands like this:

print "HELLO"

6. Save the file by pressing Ctrl + X followed by Y and Enter only if you've modified it.
7. Now, let's type Python followed by the the script name:

$ python hello.py

When you run it, you will get the following output:

The preceding command runs the script and prints out HELLO; that's all you have to do if you have a macOS or Linux system.

Installing Python on Windows

If you have Windows, you have to download and install Python.

Here are the steps which you need to follow:

1. Download Python from https://www.python.org/downloads/
2. Run it in a Command Prompt window
3. Start interactive mode with Python
4. Close with exit()

To create a script, you just use Notepad, enter the text, save the file with...

Table of contents

• Title Page
• Copyright and Credits
• Packt Upsell
• Contributor
• Preface
• Obfuscation
• Hashing
• Strong Encryption
• Other Books You May Enjoy