Implementing Cryptography Using Python

CHAPTER 5Stream Ciphers and Block Ciphers

In this chapter, you'll learn the means of support of the entire cryptographic world. You will learn how to encrypt and decrypt messages with a shared secret, which is how the vast majority of today's encryption on the Internet functions. In fact, encryption is used every day using techniques you'll learn in this chapter. This chapter introduces you to the development of stream ciphers, block ciphers, and cryptographically secure pseudorandom number generators. You'll gain an understanding of some of the analyses of the underlying algorithms and the best attacks that exist in the real world. You'll also learn the amount of security you must build in, based on the client you are serving, and how long it needs to stay secure. You'll walk away with being able to randomize every message you send, which will help you build a solid career in cryptography. Through this chapter, you'll gain cryptographic knowledge as you do the following:

• Learn how to convert between hexdigest and plaintext
• Gain an understanding of stream ciphers and CSPRNGs
• Learn about block ciphers
• Explore various modes of encryption and their weaknesses
• Gain an understanding of blocks as streams

Convert between Hexdigest and Plaintext

Before we dive into stream and block ciphers, I will show you some of the harder bits that involve the conversion between hexdigest and plaintext. To perform the conversions in Python, you'll use the binascii library. The binascii module ...