Cryptography has had an interesting history and has undergone many changes through
the centuries. It seems that keeping secrets has been important throughout the ages of
civilization for one reason or another. Keeping secrets gives individuals or groups the
ability to hide true intentions, gain a competitive edge, and reduce vulnerability.
The changes that cryptograph has undergone throughout history closely follow the
advances in technology. Cryptography methods began with a person carving messages
into wood or stone, which were then passed to the intended individual who had the
necessary means to decipher the messages. This is a long way from how cryptography is
being used today. Cryptography that used to be carved into materials is now being
inserted into streams of binary code that passes over network wires, Internet communication
paths, and airwaves, as shown in Figure 8-1.
In the past, messengers were used as the transmission mechanism, and encryption
helped protect the message in case the messenger was captured. Today, the transmission
mechanism has changed from human beings to packets carrying 0’s and 1’s passing
through network cables or open airwaves. The messages are still encrypted in case an
intruder captures the transmission mechanism (the packets) as they travel along their
Encryption is a method of transforming original data, called plaintext or cleartext, into
a form that appears to be random and unreadable, which is called ciphertext. Plaintext
is either in a form that can be understood by a person (a document) or by a computer
(executable code). Once it is transformed into ciphertext, neither human nor machine
can properly process it until it is decrypted. This enables the transmission of confidential
information over insecure channels without unauthorized disclosure. When data is
stored on a computer, it is usually protected by logical and physical access controls.
When this same sensitive...