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Top1. Introduction
In Information security, data hiding (Katzenbeisser & Petitcolas, 2000; Provos & Honeyman, 2003) is commonly used to embed secret information into an innocuous digital cover. A digital cover may be audio, video, text, still image or any digital file. The technique of hiding digital information in another digital cover is also called steganography. Steganography has been in use for a very long time. However in recent days the steganography has attracted many researchers due to enormous scope of hiding digital information in a digital cover. Different type of digital file is stored in its own specific file format. If a file format provides enough redundancy, it is used to embed secret message in it. Alternatively, changing a few bits here and there in a digital file goes unnoticed by a third party and this provides scope for hiding information. In this work we have tested the algorithm with images stored in BMP (Muttoo & Kumar, 2010a; Staples & Wienman, 2005), PNG and TIFF format (Staples & Wienman, 2005).
In this modern era, more and more communication is taking place using public digital communication networks. A message travels across many subnets, administratively controlled by independent authority, before finally reaching its destination. Encryption and steganography are used to protect the secrecy and privacy of a message by ensuring that the message is not accessed by any third party during its life period of secrecy. The purpose of Steganography is to conceal the fact that some communication is taking place. This is achieved by hiding the secret message within another seemingly innocuous message, or carrier (Kumar & Muttoo 2011; Muttoo & Kumar, 2010b). Cryptography on the other hand does so by scrambling the data so that it should not be understood to the third party (Wang, Wu, Tsai & Hwang, 2008).
The important requirement for a steganographic system is its detectability by an attacker with probability not better than random guessing, given the full knowledge of the embedding algorithm and statistical properties of cover object (Amirtharajan & Balaguru, 2009; Shih, 2008; Jung, Ha & Yoo, 2008). The distortion in cover object due to data hiding is not desirable in some applications like medical images, visual artefacts etc. In steganographic system, a digital file that is used as a carrier for hidden information is called Cover object. Cover object is also called host object. A message is text or any information that needs to be protected to ensure its privacy and secrecy. Once the message is embedded into cover object, the cover object is called stego object. Whenever a key is used to hide and extract the secret message in a steganographic system, it is called stego key.