ample: A 24-bit bitmap that has eight bits represent- ing each of the three primary colors (red, green, and blue-RGB) for each pixel. The red color alone, represented by eight bits, has 256 possible val- ues (28). The difference between a red value of 01111111 and a red value of 01111110 will be undetectable by the human eye. Therefore, the least significant bit can be used for something other than color information. If we then encode the green and the blue as well, we will have three encod- able bits, which means that three pixels will yield nine bits, one more than is required to encode an eight-bit character. So why do we care about this? In October 2001, the New York Times claimed that terrorists were using steganographic techniques to encode messages into images (by some acounts, pornographic messages at adult Web sites). While these claims were largely dismissed by security experts, it is certainly a possibility. Needless to say, security analysts have created steganalysis tools that can be used to detect and read mes- sages embedded steganographically in images and other file types. From a more practical perspective, steganographic techniques can be used to embed important information such as digital watermarks, copy- right information, and the like. Let's turn our attention now back to our e-mail message. The Session Layer We have now left the Presentation Layer. Our e-mail message is encrypted, compressed, and may have gone through an ASCII-to- EBCDIC code conversion before descending into the complexity of the Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Protocols Chapter 2 Session Layer. As before, the Presentation Layer added a header con- taining information about the services it employed. For being such an innocuous layer, the Session Layer certainly engen- ders a lot of attention. Some believe that the Session Layer could b