Cryptography in Action 61
The terms listed here are critical to understanding all forms of cryptography.
You’ll be seeing them again not only in this chapter but in later chapters
as well.Next let’s look at the two major types of cryptography: symmetric and asymmetric (aka
public-key cryptography).
Symmetric Cryptography
Symmetric algorithms do some things really well and other things not so well. Modern
symmetric algorithms are great at all of the following:
■ Preserving confidentiality
■ Increasing speed
■ Ensuring simplicity (relatively speaking, of course)
■ Providing authenticity
Symmetric algorithms have their drawbacks in these areas:
■ Key management issues
■ Lack of nonrepudiation features
First let’s focus on the defining characteristic of symmetric encryption algorithms: the
key. All algorithms that fit into the symmetric variety use a single key to both encrypt and
decrypt (hence the name symmetric). This is an easy concept to grasp if you think of a key
used to lock a gym locker as the same key used to unlock it. A symmetric algorithm works
the exactly the same way: the key used to encrypt is the same one used to decrypt.
Common Symmetric Algorithms
There are currently a myriad of symmetric algorithms available to you; a Google search
turns up an endless sea of alphabet soup of algorithms. Let’s look at some common algo-
rithms in the symmetric category:
Data Encryption Standard (DES) Originally adopted by the U.S. government in 1977, the
DES algorithm is still in use today. DES is a 56-bit key algorithm, but the key is too short to
be used today for any serious security applications.
Triple DES (3DES) This algorithm is an extension of the DES algorithm, which is three
times more powerful than the DES algorithm. The algorithm uses a 168-bit key.
Blowfish Blowfish is an algorithm that was designed to be strong, fast, and simple in its
design. The algorithm uses a 448-bit key and is optimized for use in today’s 32- and 64-bit
processors (which its predecessor DES was not). The algorithm was designed by encryption
expert Bruce Schneier.
International Data Encryption Algorithm (IDEA) Designed in Switzerland and made
available in 1990, this algorithm is seen in applications such as the Pretty Good Privacy
(PGP) system (see the section “Pretty Good Privacy” later in this chapter).