Cryptography Reference
In-Depth Information
Symmetric Encryption
4
We have now completed our discussion of the fundamentals of cryptography.
Recall from Chapter 1 that we interpreted cryptography as a toolkit and that
cryptographic primitives were the basic tools in that toolkit. In this chapter we
commence an investigation of the various primitives (tools) that cryptography
provides for use as security mechanisms. We begin by studying symmetric
encryption algorithms.
At the end of this chapter you should be able to:
• Recognise the basic differences between stream ciphers and block ciphers.
• Identify the types of application where stream ciphers and block ciphers are
most appropriate.
• Appreciate the important role that DES has played in the history of modern
cryptography.
• Identify the development history and basic design features of AES.
• Compare the properties of several different block cipher modes of operation.
In this introductory sectionwe introduce an important classification of symmetric
encryption algorithms. Note that:
• Encryption algorithms are the cryptographic primitives that most people
associate with cryptography, since they are primarily designed for providing
confidentiality. It is very important to recognise that encryption algorithms are
just one of the many components of the cryptographic toolkit, albeit important
ones.
• This chapter deals with one class of encryption algorithms, namely
symmetric
encryption algorithms. Public-key encryption is discussed in Chapter 5.
• While (symmetric) encryption algorithms are primarily designed as confiden-
tiality mechanisms, they can be used, either directly or as building blocks, in
