Steganography

Seminar topic on Steganography

Abstract on Steganography

Steganography is the technique of hiding private or sensitive information within something that appears to be nothing out of the usual. Steganography is often confused with cryptology because the two are similar in the way that they both are used to protect important information. The difference between the two is that Steganography involves hiding information so it appears that no information is hidden at all.In this paper,we describe method of Steganography based on embedding encrypted message bits using RSA Algorith min the 1st least significant (LSB Technique) and last 4 significant bits (Modulus 4 bit technique)of the pixe l of image.Here we also provide integrity using MD5 hash algorithm. The analysis shows that the PSNR is improved in the case of LSB technique. Use of hash algorithm  provides data integrity

Steganography is a form of security technique through obscurity, the science and art of hiding the existence of a message between sender and intended recipient. Steganography has been used to hide secret messages in various types of files, including digital images, audio and video. The three most important parameters for audio steganography are imperceptibility, payload, and robustness. Different applications have different requirements of the steganography technique used. This paper intends to give an overview of image steganography, its uses and techniques.

How it Works

 

The core of any steganographic method is how it encodes a single byte (8 bits) of information within the image. Some methods take advantage of the file structure of the image and hide it in special data fields. For example, in the BMP file format, the offset between the file information and pixel data can be manually specified. This presents interesting possibility of hiding an entire file between the file information and the pixel data without altering the image at all. In practice, such methods are impossible to detect visually but easy to detect with a computer: if the file size is larger than the minimum size necessary for the image size and color depth (according to the file format specification), then it probably included hidden data.
Other steganographic methods hide data by slightly modifying the pixels of the actual image by small amounts. Typically, the modification is done by changing the least significant bit (or bits) of the red, green, blue, and applicable, alpha channels of one or more pixels. This is how we proceed in our sample program.

Detection and Countermeasures

Detecting and preventing steganographic messages from being transmitted is an extremely difficult task. Depending on the circumstances, it may be impossible to prove that someone is even sending messages in the first place!

When it comes to combating (or rather detecting) physical steganographic messages, the key is really to understand all of the possible ways a message could be hidden in or on an object. For example, invisible ink that only visible when exposed to certain chemicals or ultraviolet light. There is a great history of steganography used in the real world eventually being discovered – hidden messages sent through newspapers, media, and seemingly normal communications. Detecting steganography when you don’t know what you’re looking for is partially a guessing game, and partially a pattern finding exercise.

In computing, detection of steganographically encoded packages is called steganalysis. The simplest method to detect files that may have been modified to send steganographic messages is to compare the files to known, clean originals of the files. For example, if one wanted to see if a website had been modified to hide a message in it’s image files, one could compare the image files currently on the site with the original files intended to be there. The differences in the file (if any) would reveal the steganographic message in it’s entirety.

Another common method of combating steganography is data compression. Lossful data compression (such as the JPEG image format) can completely ruin any hidden modified data bits within the file. Reducing the size of the file through compression will also significantly decrease the amount of space available for a hidden message to reside.

Types of encoding

Least Significant Bit encoding

This method is the more popular one among encoding images. Programs that use the Least Significant Bit, or LSB,method encode the message in the least significant bit of every byte in an image. By doing so, the value of each pixel is changed slightly, but not enough to make significant changes to the image. In a 24-bit image, 3 bytes are used for each pixel, so each pixel could encode 3 bits of a secret message.The altered image would look identical to the human eye, even when compared to the original. However, 24-bit images are quite large, and are not a popular method of sending images around the web, so the fact that they are so large would arouse suspicion.A more plausible container image would be a 256 color image, where 1 byte is used for each pixel. A 640 x 480 image of this quality would be able to store 300 kilobits of data. With a large enough image, one could even hide an image within another image.Popular commercial programs that use LSB encoding include White Noise Storm and S-Tools.

Frequency Domain encoding

This method encodes messages within images by working with the 2-dimensional Fast Fourier Transform, or 2-D FFT of the container image. The 2-D FFT separates the frequencies of the image into rings centered around an axis. Those rings closest to the axis represent the low frequencies of the image, and those furthest away represent the high frequencies. In the frequency domain encoding method, the secret message is encoded in the middle frequencies of the image. This is done by converting the message text to bits and overlaying these bits in a ring shape in the desired frequency band on the 2-D FFT. Although the ring of bits appears dark and outstanding on the 2-D FFT, the effect on the image itself is very slight. Also, an image encoded by this method is able to better withstand noise, compression, translation, and rotation, than images encoded by the LSB method. All of the images we worked with in this project were encoded by the nPhaze Boys in this manner using Matlab.

DIFFERENT KINDS OF STEGANOGRAPHY

The four main categories of file formats that can be used for steganography are: 

• Text 
• Images 
• Audio 
• Protocol  

Text steganography:

Hiding information in text is the most important method of steganography. It hides the text behind some other text file. It is the a difficult form of steganography as the redundant amount of text to hide the secret message is scarce in text files

Image steganography:

It is one of the most commonly used technique because of the limitation of the Human visual System(HVS). Human eye cannot detect the vast range of colors and an insignificant change in the quality of an image that results from steganography.

Audio steganography:

It  is  also  a  difficult  form  of steganography  as  humans are  able  to  detect  a  minute  change in the quality of audio

Protocol steganography:

The term protocol steganography is to embedding information within network protocols such as TCP/IP. We hide information in the header of a TCP/IP packet in some fields that can be either optional or are never used.


References
http://www.ijceronline.com/papers/Vol2_issue7/AF02701900193.pdf
http://ieeexplore.ieee.org/
http://easybmp.sourceforge.net/steganography.html
https://www.clear.rice.edu/elec301/Projects01/steganosaurus/background.html
http://www.garykessler.net/library/steganography.html
http://www.ijettjournal.org/volume-4/issue-7/IJETT-V4I7P186.pdf
http://www.ijettjournal.org/volume-4/issue-7/IJETT-V4I7P186.pdf