Network Security Bible, 2nd Edition

Chapter 21. Covert Communication

IN THIS CHAPTER

• Introducing steganography

• Examining the origins of steganography

• Understanding how steganography relates to network security

• Comparing steganography and cryptography

• Examining types of steganography

Steganography derives from the Greek word steganos (meaning covered or secret) and graphy (writing or drawing). On the simplest level steganography is hidden writing, whether it consists of invisible ink on paper or copyright information hidden within an audio file.

Today, steganography, stego for short, is most often associated with the high-tech variety, where data is hidden within other data in an electronic file. For example, a Word document might be hidden inside of an image file. This is done by replacing the least important or most redundant bits of data in the original file — bits that the human eye or ear hardly miss — with hidden data bits.

Where cryptography scrambles a message into a code to obscure its meaning, steganography hides the message entirely. These two secret communication technologies can be used separately or together, for example, by first encrypting a message, then hiding it in another file for transmission.

As the world becomes more anxious about the use of any secret communication and governments create regulations to limit cryptography and the use of encryption, steganography's role is gaining prominence.

Where Hidden Data Hides

Unlike a word-processed file where you're likely to notice letters missing here and there, ...