Cryptography Reference
In-Depth Information
Chapter 5
More About Block Ciphers
A block cipher is much more than just an encryption algorithm. It can be used as
a versatile building block with which a diverse set of cryptographic mechanisms
can be realized. For instance, we can use them for building different types of block-
based encryption schemes, and we can even use block ciphers for realizing stream
ciphers. The different ways of encryption are called
modes of operation
and are
discussed in this chapter. Block ciphers can also be used for constructing hash func-
tions, message authentication codes which are also knowns as MACs, or key estab-
lishment protocols, all of which will be described in later chapters. There are also
other uses for block ciphers, e.g., as pseudo-random generators. In addition to modes
of operation, this chapter also discusses two very useful techniques for increasing
the security of block ciphers, namely key whitening and multiple encryption.
In this chapter you will learn
the most important modes of operation for block ciphers in practice
security pitfalls when using modes of operations
the principles of key whitening
why double encryption is not a good idea, and the meet-in-the-middle attack
triple encryption
