27-08-2014, 11:19 AM
Steganography
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ABSTRACT:
In this paper, we aim to present a general introduction to steganography or data-hiding as
it is sometimes just known. We then turn to data-hiding in images. When examining these
data-hiding techniques, we bear in mind Bender's specifications, such as degradation of
the cover data must be kept to a minimum, and the hidden data must be made as immune
as possible to possible attack from manipulation of the cover data.
Steganography in images has truly come of age with the invention of fast, powerful
computers. Software is readily available off the Internet for any user to hide data inside
images. These softwares are designed to fight illegal distribution of image documents by
stamping some recognisable feature into the image.The most popular technique is Least
Significant Bit insertion, which we will look at. Also, we look at more complex methods
such as masking and filtering, and algorithms and transformations, which offer the most
robustness to attack, such as the Patchwork method which exploits the human eye's
weakness to luminance variation.
we will take a brief look at steganalysis, the science of detecting hidden messages and
destroying them. We conclude by finding that steganography offers great potential for
securing of data copyright, and detection of infringers. Soon, through
steganography,personal messages,files, all artistic creations, pictures, and songs can be
protected from piracy
INTRODUCTION:
Steganography, from the Greek, means covered, or secret writing, and is a long-practised
form of hiding information. Although related to cryptography, they are not the same.
Steganography's intent is to hide the existence of the message, while cryptography
scrambles a message so that it cannot be understood.
More precisely,
``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.''
Steganography includes a vast array of techniques for hiding messages in a variety of
media. Among these methods are invisible inks, microdots, digital signatures, covert
channels and spread-spectrum communications. Today, thanks to modern technology,
steganography is used on text, images, sound, signals, and more.
In the following sections we will try to show how steganography can and is being used
through the media of images.
IMAGES:
To a computer, an image is an array of numbers that represent light intensities at various
points, or pixels. These pixels make up the image's raster data. An image size of 640 by
480 pixels, utilizing 256 colors (8 bits per pixel) is fairly common. Such an image would
contain around 300 kilobits of data.
Digital images are typically stored in either 24-bit or 8-bit per pixel files. 24-b
Image Compression:
Image compression offers a solution to large image files. Two kinds of image
compression are lossless and lossy compression. Both methods save storage space but
have differing effects on any uncompressed hidden data in the image.
Lossy compression, as typified by JPEG (Joint Photographic Experts Group) format files,
offers high compression, but may not maintain the original image's integrity. This can
impact negatively on any hidden data in the image. This is due to the lossy compression
algorithm, which may ``lose'' unnecessary image data, providing a close approximation to
high-quality digital images, but not an exact duplicate. Hence, the term``lossy''
compression. Lossy compression is frequently used on true-colour images, as it offers
high compression rates.
Lossless compression maintains the original image data exactly; hence it is preferred
when the original information must remain intact. It is thus more favoured by
steganographic techniques. Unfortunately, lossless compression does not offer such high
compression rates as lossy compression. Typical examples of lossless compression
formats are Compuserve's GIF (Graphics Interchange Format) and Microsoft's BMP
(Bitmap) format.
Advantages of LSB Insertion:
Major advantage of the LSB algorithm is it is quick and easy.
There has also been steganography software developed which work around LSB
color alterations via palette manipulation.
LSB insertion also works well with gray-scale images.
Algorithms and transformations:
Because they are high quality colour images with good compression, it is desirable to use
JPEG images across networks such as the Internet. Indeed, JPEG images are becoming
abundant on the Internet.
JPEG images use the discrete cosine transform (DCT) to achieve compression. DCT is a
lossy compression transform, because the cosine values cannot be calculated precisely,
and rounding errors may be introduced. Variances between the original data and the
recovered data depends on the values and methods used the calculate the DCT.
SYSTEM DESIGN:
These are the steps followed in image hiding while transmission and de noising after
receiving:
1. Get a cover image (publicly accessible material)
2. Take the information to be hidden (message or image)
3. Combine cover image with the information to be hidden(we follow LSB
algorithm for this)
4. While transmission it will be corrupted by noise
5. Use any of the filtering methods, ex: wiener filtering for de noising in wavelet
domain
6. Here filter is employed in order to remove the noise
7. During extraction a password check is provided
8. If password is matched then extraction of hidden information
Conclusion:
In this paper, we take an introductory look at steganography. Several methods for hiding
data in, images were described, with appropriate introductions to the environments of
each medium, as well as the strengths and weaknesses of each method.The key algorithm
for designing the steganography system has been dealt. Most data-hiding systems take
advantage of human perceptual weaknesses, but have weaknesses of their own. We
conclude that for now, it seems that no system of data-hiding is totally immune to attack.
However, steganography has its place in security. Though it cannot replace cryptography
totally, it is intended to supplement it. Its application in watermarking and fingerprinting,
for use in detection of unauthorised, illegally copied material, is continually being
realised and developed.
Also, in places where standard cryptography and encryption is outlawed, steganography
can be used for covert data transmission. Steganography can be used along with
cryptography to make an highly secure data high way.Formerly just an interest of the
military, Steganography is now gaining popularity among the masses. Soon, any
computer user will be able to put his own watermark on his artistic creations.