27-07-2012, 02:02 PM
ANALYSIS OF VARIOUS STEGANOGRAPHY ALGORITHMS AND THEIR IMPLEMENTATION
VARIOUS STEGANOGRAPHY.pdf (Size: 1.68 MB / Downloads: 78)
ABSTRACT :
The rapid development of data transfer through internet has made it easier to
send the data accurate and faster to the destination. There are many transmission media to
transfer the data to destination like e-mails, social sites etc. At the same time it is may be
easier to modify and misuse the valuable information through hacking. So, in order to
transfer the data securely to the destination without any modifications, there are many
approaches like cryptography and steganography.
This project report deals with image steganography as well as with the
different security issues, general overview of cryptography, steganography and digital
watermarking approaches.
Also it provides in-depth discussions of different steganographic algorithms
like Least Significant Bit (LSB) algorithm, JSteg Hide & Seek and F5 algorithms. It also
compares those algorithms in terms of speed, accuracy and security. It also offers a
chance to put the theory into practice by way of a piece of software designed to maximise
learning in the fields. This paper can therefore be split into two parts: Research and
Software Development.
INTRODUCTION
An overview of Internet Security
Since the rise of the Internet one of the most important factors of information
technology and communication has been the security of information. Everyday tons
of data are transferred through the Internet through e-mail, file sharing sites, social
networking sites etc to name a few. As the number of Internet users rises, the concept
of Internet security has also gain importance. The fiercely competitive nature of the
computer industry forces web services to the market at a breakneck pace, leaving
little or no time for audit of system security, while the tight labour market causes
Internet project development to be staffed with less experienced personnel, who may
have no training in security. This combination of market pressure, low
unemployment, and rapid growth creates an environment rich in machines to be
exploited, and malicious users to exploit those machines.
Where Steganography & Cryptography fits
Cryptography was created as a technique for securing the secrecy of
communication and many different methods have been developed to encrypt and
decrypt data in order to keep the message secret. Unfortunately it is sometimes not
enough to keep the contents of a message secret, it may also be necessary to keep the
existence of the message secret. The technique used to implement this, is called
steganography.
The word "Steganography" is of Greek origin and means "covered or hidden
writing". The main aim in steganography is to hide the very existence of the message
in the cover medium. Steganography and cryptography are counter parts in digital
security the obvious advantage of steganography over cryptography is that messages
do not attract attention to themselves, to messengers, or to recipients. Also, the last
decade has seen an exponential growth in the use of multimedia data over the
Internet. These include Digital Images, Audio and Video files. This rise of digital
content on the internet has further accelerated the research effort devoted to
steganography. The initial aim of this study was to investigate steganography and
how it is implemented. Based on this work a number of common methods of
steganography could then be implemented and evaluated. The strengths and
weaknesses of the chosen methods can then be analysed. To provide a common frame
of reference all of the steganography methods implemented and analysed used BMP
images.
LSB algorithm:
LSB (Least Significant Bit) substitution is the process of adjusting the
least significant bit pixels of the carrier image. It is a simple approach for embedding
message into the image. The Least Significant Bit insertion varies according to
number of bits in an image. For an 8 bit image, the least significant bit i.e., the 8th bit
of each byte of the image is changed to the bit of secret message. For 24 bit image,
the colours of each component like RGB (red, green and blue) are changed. LSB is
effective in using BMP images since the compression in BMP is lossless. But for
hiding the secret message inside an image of BMP file using LSB algorithm it
requires a large image which is used as a cover. LSB substitution is also possible for
GIF formats, but the problem with the GIF image is whenever the least significant bit
is changed the whole colour palette will be changed. The problem can be avoided by
only using the gray scale GIF images since the gray scale image contains 256 shades
and the changes will be done gradually so that it will be very hard to detect.
JSTEG algorithm:
JSteg algorithm is one of the steganographic techniques for embedding
data into JPEG images. The hiding process will be done by replacing Least
Significant Bits (LSB). JSteg algorithm replaces LSBs of quantized Discrete Courier
Transform (DCT) coefficients. In fact, the JSteg algorithm only differs from the Hide
& Seek algorithm because it embeds the message data within the LSBs of the DCT
coefficients of c, rather than its pixel values. Before the embedding process begins,
the image is converted to the DCT domain in 8x8 blocks such that the values of ci
switch from pixel values to DCT coefficients. In order for the values to be presented
as whole numbers, each 8x8 block is quantised according to a Quantisation Table Q.
The result is where the embedding algorithm operates. An example of an 8x8 DCT
block is shown in Figure 10. In this process the hiding mechanism skips all
coefficients with the values of 0 or 1. This algorithm is resistant to visual attacks and
offers an admirable capacity for steganographic messages. It has high capacity and
had a compression ratio of 12%. JSteg algorithm is restricted for visual attacks and it
is less immune for statistical attacks. Normally, JSteg embeds only in BMP images.
In these BMP images, the content of the image is transformed into ‘frequency
coefficients’ so as to achieve storage in a very compressed format. There is no visual
attack in the sense presented here, due to the influence of one steganographic bit up to
256 pixels.
CONCLUSION
The Stegenographic schemes which were present for more than 1000 years
were studied and analyzed in details in this report. Various algorithms were analyzed,
compared and implemented.
For designing the steganographic application, we worked on different phases
like encryption, decryption and data transmission. An application for sending the
personal data securely to the destination has been developed successfully.
The design phase is the primary phase, which gives a brief idea about the
different levels used for developing an application with the help of block diagrams.
The software is designed in a user friendly manner. So, it is simple to use for
developing a prototype of the application.