(     ) 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.