Book Image

Cryptography Engineering

By : Niels Ferguson‚ÄØ, Tadayoshi Kohno, Bruce Schneier
Book Image

Cryptography Engineering

By: Niels Ferguson‚ÄØ, Tadayoshi Kohno, Bruce Schneier

Overview of this book

Cryptography is vital to keeping information safe, in an era when the formula to do so becomes more and more challenging. Written by a team of world-renowned cryptography experts, this essential guide is the definitive introduction to all major areas of cryptography: message security, key negotiation, and key management. You'll learn how to think like a cryptographer. You'll discover techniques for building cryptography into products from the start and you'll examine the many technical changes in the field. After a basic overview of cryptography and what it means today, this indispensable resource covers such topics as block ciphers, block modes, hash functions, encryption modes, message authentication codes, implementation issues, negotiation protocols, and more. Helpful examples and hands-on exercises enhance your understanding of the multi-faceted field of cryptography.
Table of Contents (9 chapters)

Chapter 4
Block Cipher Modes

Block ciphers encrypt only fixed-size blocks. If you want to encrypt something that isn't exactly one block long, you have to use a block cipher mode. That's another name for an encryption function built using a block cipher.

Before proceeding with this chapter, we have one word of warning. The encryption modes that we talk about in this chapter prevent an eavesdropper from reading the traffic. They do not provide any authentication, so an attacker can still change the message—sometimes in any way she wants. Many people find this surprising, but this is simple to see. The decryption function of an encryption mode simply decrypts the data. It might produce nonsense, but it still decrypts a (modified) ciphertext to some (modified and possibly nonsensical) plaintext. You should not rely on the fact that nonsensical messages do no harm. That involves relying on other parts of the system, which all too often leads to grief. Furthermore, for some...