09-10-2012, 05:45 PM
Covered writing
Covered writing.pptx (Size: 179.02 KB / Downloads: 24)
INTRODUCTION
Steganography comes from the Greek and literally means,"Covered writing“
It is one of various data hiding techniques, which aims at transmitting a message on a channel where some other kind of informatio is already being transmitted.
The goal of steganography is to hide messages inside other “harmless” messages in a way that does not allow any “enemy” to even detect that there is a second secret message present.
It is mainly used by companies or any miltary operation or investigation for hiding data
In the cases when this is possible, either because the workingcompany does not allow encrypted email or the local government does not approve of encrypt communication. This is where steganography can come into play.
Another application of steganography is the protection of sensitive data. A file system can be hidden in random looking files in ahard disk, needing a key to extract the original files.
The major concern of steganography is stealth, because if an attacker, either passive or active, can detect the presence of the message, from that point he can try to extract it and, if encrypted, to decrypt it.
If the stego-data can be transmitted over the selected channel, and this is usually the case with all the media that are used, like images or sounds, then the embedded data will be preserved along with them
SOME DEFINITIONS
Cover medium: This is the medium in which we want to hide data
Embedded message: This is the hidden message we want to put in the cover
Stegokey:This is represented by the key or password of the information that stored in cover meadium.
Stego-medium: This is the final piece of information that the casual observer can see.
Cover-medium + embedded-message = stego-message
IMAGE FILES
To a computer, an image is an array of numbers that represent an array of numbers that represent light intensities at various points or pixels
A common image size is 640 * 480 and 256 colors (or 8 bits per pixel). Such an image could contain about 300 kb of data.
Digital images ate typically stored as either 24-bit or 8-bit files
A 24-bit image provides the most space for hiding information,however, it can be quite large except for the JPEG images.
File compression
There are two types of file compression methods- lossless and lossy.
Lossless compression lets us reconstruct the original message exactly; therefore it is preferred when the original information must remain intact
Lossless compression us typical of mages saved as GIF and 8-bit BMP.
A stego-key (a type of password) may also be used to hide, and then later decode, the message.
Embedding data
Embedding data, which is to be hidden, into an image requires two files.
The first is the innocent looking image that will hold the hidden information, called the cover image.
The second file is the message- the information to be hidden.
A message may be plain text, cipher text, other images, or anything that can be embedded in a bit stream
A stego-key (a type of password) may also be used to hide, and then later decode, the message.