29-08-2013, 03:01 PM
Steganography and Steganalysis: Different Approaches
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Abstract
Steganography is the technique of hiding confidential information within any
media. Steganography is often confused with cryptography because the two are
similar in the way that they both are used to protect confidential information. The
difference between the two is in the appearance in the processed output; the
output of steganography operation is not apparently visible but in cryptography
the output is scrambled so that it can draw attention. Steganlysis is process to
detect of presence of steganography. In this article we have tried to elucidate the
different approaches towards implementation of steganography using
‘multimedia’ file (text, static image, audio and video) and Network IP datagram
as cover. Also some methods of steganalysis will be discussed.
Introduction
The objective of steganography is to hide a secret message within a cover-media
in such a way that others cannot discern the presence of the hidden message.
Technically in simple words “steganography means hiding one piece of data
within another”.
Modern steganography uses the opportunity of hiding information into digital
multimedia files and also at the network packet level.
Hiding information into a media requires following elements [2]
•The cover media© that will hold the hidden data
•The secret message (M), may be plain text, cipher text or any type of data
•The stego function (Fe) and its inverse (Fe-1)
•An optional stego-key (K) or password may be used to hide and unhide the
message.
Still imagery steganography
The most widely used technique today is hiding of secret messages into a digital
image. This steganography technique exploits the weakness of the human visual
system (HVS). HVS cannot detect the variation in luminance of color vectors at
higher frequency side of the visual spectrum. A picture can be represented by a
collection of color pixels. The individual pixels can be represented by their optical
characteristics like 'brightness', 'chroma' etc. Each of these characteristics can be
digitally expressed in terms of 1s and 0s.
For example: a 24-bit bitmap will have 8 bits, representing each of the three-
color values (red, green, and blue) at each pixel. If we consider just the blue
there will be 28 different values of blue. The difference between 11111111 and
11111110 in the value for blue intensity is likely to be undetectable by the
human eye. Hence, if the terminal recipient of the data is nothing but human
visual system (HVS) then the Least Significant Bit (LSB) can be used for
something else other than color information
Echo Hiding:
In this method the secret message is embedded into cover audio signal as
an echo. Three parameters of the echo of the cover signal namely
amplitude, decay rate and offset from original signal are varied to
represent encoded secret binary message. They are set below to the
threshold of Human Auditory System (HAS) so that echo can’t be easily
resolved.
Video files are generally consists of images and sounds, so most of the
relevant techniques for hiding data into images and audio are also applica-
ble to video media. In the case of Video steganography sender sends the
secret message to the recipient using a video sequence as cover media.
Optional secret key ‘K’ can also be used during embedding the secret
message to the cover media to produce ‘stego-video’.
After that the stego-video is communicated over public channel to the re-
ceiver. At the receiving end, receiver uses the secret key along with the
extracting algorithm to extract the secret message from the stego-object
Conclusion
In this paper, different techniques are discussed for embedding data in text,
image, audio/video signals and IP datagram as cover media. All the proposed
methods have some limitations. The stego multimedia produced by men-
tioned methods for multimedia steganography are more or less vulnerable to
attack like media formatting, compression etc. In this respect, IP datagram
steganography technique is not susceptible to that type of attacks. Stegana-
lyis is the technique to detect steganography or defeat steganography. The
research to device strong steganographic and steganalysis technique is a con-
tinuous process.