(第1空)( ) 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.