STEGANOGRAPHIC TECHNIQUES
A. Substitution Technique
In the substitution technique ; the redundant parts
are covered with a secret message. This technique
includes the Least Significant Bit Substitution method ,
where we choose a subset of cover elements and
substitute the least significant bits of each element by the
message bits .Message may be encrypted or compressed
before hiding. A pseudorandom number generator may
be used to spread the secret message over the cover in a
random manner. This is an easy method but is vulnerable
to corruption due to small changes in carrier.
B. Transform Domain Technique
In the transfer domain technique; the secret message
is embedded in the transform space (e.g. frequency
domain) of the cover. An example of this method
includes the Discrete Cosine Transform (DCT) domain.
The cover image is split into 8*8 blocks and each block
is used to encode one message bit. The blocks are chosen
in a pseudorandom manner. The relative size of two
predefined DCT coefficients is modulated using the
message bit. The two coefficients are chosen from
middle frequencies.
C. Spread Spectrum Technique
This technique uses the concept of spread spectrum .
The message is spread over a wide frequency bandwidth.
The signal to noise ratio in every frequency band is so
small that it is difficult to detect. Even if parts of
message are removed from several bands, enough
information is present in other bands to recover the
information. Thus it is difficult to remove the message
completely without entirely destroying the cover .It is a
very robust technique that finds application in military
communication.
D. Statistical Techniques
In the statistical techniques , the information is
encoded by changing several properties of the cover. The
cover is split into blocks and each block is used to hide
one message bit .If the message bit is one, then the cover
block is modified otherwise the cover block is not
modified. This technique is difficult to apply because a
good test must be found that allows for proper
distinction between modified and unmodified cover
blocks.
E. Distortion Techniques
The information is stored by distorting the signal.
The encoder applies a sequence of modifications to the
cover . This sequence corresponds to the secret message
. The decoder measures the differences between the
original cover and the distorted cover to detect the
sequence of modifications and consequently recover the
secret message. This method is not used in many
applications because the decoder must have access to the
original cover.
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STEGANOGRAPHIC TOOLS
Blindside
Blindside is an application of steganography that
allows one to conceal a file, or set of files within a
standard computer image. The new image looks
identical to the human eye, but can contain up to 50k or
so of secret data. The hidden files can also be password
encrypted, to prevent unauthorised access to their data.
Data Marking Technologies
DataMark Technologies currently market four digital
steganography products - StegComm for confidential
multimedia communication, StegMark for digital
watermarking of digital storage media, StegSafe for
digital storage and linkage and StegSign for e-commerce
transactions. Each software product is packaged into a
Standard version and a Professional version.
Digital Picture Envelope
Digital Picture Envelope is a program you can make
your secret data imperceptible to any human eyes. So,
you can store/send it very safely in/through your
computer. Actually, it can embed your secret data in a
vessel image (we call it a "dummy" image, or a "picture
envelope") without changing the visual quality of the
dummy image. It does not change even the file size. If
you want to see the secret data, you can easily restore it
from the secret- embedded dummy image.
Gifshuffle
The program gifshuffle is used to conceal messages
in GIF images by shuffling the colourmap, which leaves
the image visibly unchanged. gifshuffle works with all
GIF images, including those with transparency and
animation, and in addition provides compression and
encryption of the concealed message.
Hide4PGP
Hide4PGP is a freeware program distributed as
source code in ANSI C and precompiled executables for
DOS (any version but 1.x - is there one outside the
museum?), OS/2 (Warp and up), and the Win32 console
(9x and NT). It's purpose is to hide any data in a way
that the viewer or listener does not recognize any
difference.
Invisible secrets
Invisible Secrets hides your private data into
innocent looking files, like pictures, or web pages. It also
features: strong encryption algorithms; a locker that
allows you to password protect certain applications; a
password management solution and a real-random
password generator; a shredder that helps you destroy
beyond recovery files, folders and internet traces; the
ability to create self-decrypting packages; secured
password transfer.
JPHIDE and JPSEEK
JPHIDE and JPSEEK are programs which allow you
to hide a file in a jpeg visual image. There are lots of
versions of similar programs available on the internet but
JPHIDE and JPSEEK are rather special. The design
objective was not simply to hide a file but rather to do
this in such a way that it is impossible to prove that the host file contains a hidden file. Given a typical visual
image, a low insertion rate (under 5%) and the absence
of the original file, it is not possible to conclude with any
worthwhile certainty that the host file contains inserted
data. As the insertion percentage increases the statistical
nature of the jpeg coefficients differs from "normal" to
the extent that it raises suspicion. Above 15% the effects
begin to become visible to the naked eye. Of course
some images are much better than others when used a
host file - plenty of fine detail is good. A cloudless blue
sky over a snow covered ski paradise is bad. A waterfall
in a forest is probably ideal.
Snow
The program snow is used to conceal messages in
ASCII text by appending whitespace to the end of lines.
Because spaces and tabs are generally not visible in text
viewers, the message is effectively hidden from casual
observers. And if the built-in encryption is used, the
message cannot be read even if it is detected.
Steg Party
StegParty is a system for hiding information inside of
plain-text files. Unlike similar tools currently available it
does not use random gibberish to encode data -- it relies
on small alterations to the message, like changes to
spelling and punctuation. Because of this you can use
any plain-text file as your carrier , and it will be more-orless
understandable after the secret message is
embedded.
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http://www.rimtengg.com/coit2007/procee ... dfs/64.pdf
(I am serious)
