A SEMINAR REPORT On STEGANOGRAPHY


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INTRODUCTION

Digital communication has become an essential part of infrastructure nowadays, a lot of applications are Internet-based and in some cases it is desired that the communication be made secret. Two techniques are available to achieve this goal: one is cryptography, where the sender uses an encryption key to scramble the message, this scrambled message is transmitted through the insecure public channel, and the reconstruction of the original, unencrypted message is possible only if the receiver has the appropriate decryption key. The second method is steganography, where the secret message is embedded in another message. Using this technology even the fact that a secret is being transmitted has to be secret There are two main directions in information hiding: protecting only against the detection of a secret message by a passive adversary, and hiding data so that even an active adversary cannot remove it. The classic situation, known as Simmons’ “Prisoners’ Problem”, is the following: Alice and Bob are in jail and try to discuss an escape plan, but all their communication can be observed by the warden. If their plan or the fact that they are discussing an escape plan were detected they would be transferred to a more secure prison. So they can only succeed if Alice can send messages to Bob so that the warden can’t even detect the presence of a secret .

Fingerprinting and Watermarking

so that one does not have to store distinctly the images, and connected information. When the purpose is the protection of intellectual property, we can make a distinction between fingerprinting and watermarking. In the case of watermarking copyright information is embedded in a digital media, and this media is transmitted to users. Fingerprinting embeds separate mark in the copies of digital media, this embedded information serves as a serial number, and it can be detected who supplied this media to third parties. Nowadays steganography is more and more important in publishing and broadcasting industries, where the embedding of copyright marks or serial numbers is needed in digital films, photos and other multimedia products. Some steganographic applications are able to scan the Internet, and to detect a copy of a specific image, or the modified image is published – so an illegal usage of a copyrighted image can be detected. In the case of audio materials, the automatic monitoring of radio advertisements is also possible, the advertiser can automatically count how many times a specific advertisement was transmitted by a given radio station. Another possible application in the case of still images is to embed captions and other information into the picture.

Least Significant Bit Insertion

Usually 24-bit or 8-bit files are used to store digital images. The former one provides more space for information hiding, however, it can be quite large. The colored representations of the pixels are derived from three primary colors: red, green and blue. 24-bit images use 3 bytes for each pixel, where each primary color is represented by 1 byte. Using 24-bit images each pixel can represent 16,777,216 color values. We can use the lower two bits of these color channels to hide data, then the maximum color change in a pixel could be of 64-color values, but this causes so little change that is undetectable for the human vision system. This simple method is known as Least Significant Bit insertion [4], [15]. Using this method it is possible to embed a significant amount of information with no visible degradation of the cover image.