10-09-2016, 04:33 PM
1454508594-newreport12.pdf (Size: 1.43 MB / Downloads: 10)
One of the reasons that intruders can be successful is the most of the information
they acquire from a system is in a form that they can read and comprehend.
Intruders may reveal the information to others, modify it to misrepresent an
individual or organization, or use it to launch an attack. One solution to this
problem is, through the use of steganography. Steganography is a technique of
hiding information in digital media. It is the science and art of concealing writing
or messages. For as long as there have been secrets, there has been a need for
people to hide their secrets. Steganography is often confused with cryptography,
though they are actually two separate fields. Cryptography is the science of making
a message unreadable without a password or key. Steganography however, deals
with hiding the fact that there even is a secret message at all. Steganography is a
very important field in today’s world, due to the lack of privacy in the modern era.
Steganography allows people to communicate without the scrutiny of others,
because nobody will even know there is a secret message encoded. Steganography
hide the secrete message within the host data set and presence imperceptible and is
to be reliably communicated to a receiver. The host data set is purposely corrupted,
but in a covert way, designed to be invisible to an information analysis.
1.1. History of Steganography
Throughout history Steganography has been used to secretly communicate
information between people.
Some examples of use of Steganography in past times are:
1. During World War 2 invisible ink was used to write information on pieces of
paper so that the paper appeared to the average person as just being blank
pieces of paper. Liquids such as milk, vinegar and fruit juices were used,
because when each one of these substances are heated they darken and
become visible to the human eye.
2. In Ancient Greece they used to select messengers and shave their head, they
would then write a message on their head. Once the message had been
written the hair was allowed to grow back. After the hair grew back the
messenger was sent to deliver the message, the recipient would shave off the
messengers hair to see the secrete message.
2. System Description
In order to hide a message within a digital message, we take advantage of the least
significant bit within each pixel of an image. Each pixel is made up of three eight
bit integers that store the value of the color in each image. For example, 255 red,
255, green, and 0 blue makes the color yellow. By replacing the least significant bit
in each of these color values, it is possible to hide a secret message, bit by bit,
without changing the color values too much, as illustrated in Example 1.
(Unaltered least significant bit. Encoded least significant bit.)
Red Pixel Value Green Pixel Value Blue Pixel Value
Unaltered: 1111 1111 1111 1111 0000 0000
Encoded: 1111 1111 1111 1110 0000 0001
Message: 1 0 1
Example 1: To hide the three bit message ‘101’ in a pixel of the color yellow.
The algorithm used for Encryption and Decryption in this application provides
using several layers lieu of using only LSB layer of image. Writing data starts from
last layer (8st or LSB layer); because significant of this layer is least and every
upper layer has doubled significant from its down layer. So every step we go to
upper layer image quality decreases and image retouching transpires.
The encrypt module is used to hide information into the image; no one can see that
information or file. This module requires any type of image and message and gives
the only one image file in destination.
The decrypt module is used to get the hidden information in an image file. It take
the image file as an output, and give two file at destination folder, one is the same
image file and another is the message file that is hidden it that.
Before encrypting file inside image we must save name and size of file in a definite
place of image. We could save file name before file information in LSB layer and
4
save file size and file name size in most right-down pixels of image. Writing this
information is needed to retrieve file from encrypted image in decryption state.
Steganographic Decoding Process
Decoding and recovering the hidden message follows the basic process outlined in
Figure 8. This process reverses the effects of the encoding process and reveals the
secret message to an authorized user.
Figure 8: Steganographic Decoding Process. First, the Header is decoded, XOR
decrypted, and analyzed to determine the dimensions and message type. Next, the
Message is decoded and XOR decrypted before finally being reconstituted using
the dimension data from the Header.
First the encrypted Header values are recovered from the Cover Medium Image
and decrypted using the same XOR encryption key used during the encoding
process. The Header dimension value (length for text message; width times height
for image message) is used to determine the stop value for the recovery algorithm,
thereby reducing the complexity and speeding up the recovery process.
Next, the program recovers the entire encrypted Message from the Cover Medium
Image by using the Header Dimensions to determine when to stop. The recovered
Message is decrypted using the same XOR encryption key used during encoding.
Finally, if the message type is an image, the program uses the height/width
dimensions from the recovered Header to reconstruct the original image from the
decrypted message values for display.