（  ）is the science of hiding information. Whereas .the  goal of cryptography is tomake dataulueadable by a third party, the goal of steganography is to hide the data from athirdparty.In this rticle, I will discuss what steganography is; what purposes it seryes,  and will provide an example using available software.
       There is  a large number of steganographic（  ）that most of us are  familiar with  (especially if you watch a lot of spy movies !),ranging from invisible ink and microdots to  secreting a hidden message in the second letter of each word of a lage body of text and  spreads  spectrum  radio  communication. With computers  and  networks,there are many other ways of hiding information ,such as:
 >  Covert channels (e.g.,Loki and some distributed denial-of-service tools use the Internet Control（  ）Protocol, or ICMP,as the communications  channel  between the "bad guy" and a compromised system)
 > Hidden text within web pages
 > Hiding files in "plain  sight"  (e.g.,what better place to "hide a file than with an important sounding name in the c:\winnt\system32 directory?）
 >  Null ciphers (e.g., using the first letter of each word  to  from  a  hidden message in and otherwise innocuous text)
     Steganography today ,however,is significantly more（  ）than the examples above suggest, allowing a user to hide large amounts of infromation within image and audio files.these forms of steganography often are used in conjunction with cryprography so that the information is doubly protected ;first it is encrypted and then hidden so that an adversary has to first find the information (an often difficult task in and of itself ) and then  decrypt it.
     The simplest  approach to hiding data within an image flile is  callde（  ）significant bit  insertion in this method we can take the binary  representation of the hidden data  and overwirit the bit of each byte within the cover image . if we are using 24-bit color the amount of change  well be mininmal and indiscerible to the human eye.