Computer and internet are the major media that connects different parts of the world as one global virtual world in this modern era. That’s why we can exchange lots of information easily at any distance within seconds of time. But the confidential data need to be transferred should be kept confidential till the destination.
Steganography: General Overview
Due to advances in ICT (Information and Communication Technology), most of information is kept electronically. Consequently, the security of information has become a fundamental issue. Besides cryptography, steganography can be employed to secure information. Steganography is a technique of hiding information in digital media. In contrast to cryptography, the message or encrypted message is embedded in a digital host before passing it through the network, thus the existence of the message is unknown. Besides hiding data for confidentiality, this approach of information hiding can be extended to copyright protection for digital media: audio, video, and images.
Nowadays, thanks to the stunningly fast advancement of the computer and network technology, people can easily send or receive secret information in various forms to or from almost any remotest part of the world through the Internet within seconds. In fact, there might be tons of secret information being transmitted and exchanged on the Internet at this particular point of time. However, important secret messages may run high risks of leaking out while they are being transmitted or exchanged over some public communication channel. Therefore, how to achieve safe secret communication is an important field of research.
Steganography is the idea of hiding private or sensitive data or information within something that appears to be nothing out of the normal. The word steganography comes from the Greek Steganos, which mean covered or secret and –graphy mean writing or drawing. Therefore, steganography means, literally, covered writing. Steganography is the art and science of hiding information such that its presence cannot be detected and a communication is happening. Secret information is encoding in a manner such that the very existence of the information is concealed. Paired with existing communication methods, steganography can be used to carry out hidden exchanges. Steganographic technologies are a very important part of the future of Internet security and privacy on open systems such as the Internet. Although steganography is an ancient subject, the modern formulation of it is often given in terms of the prisoner’s problem proposed by an author who has to be capturing a stegano image for security, where two inmates wish to communicate in secret to hatch an escape plan. All of their communication passes through a warden who will throw them in solitary confinement should she suspect any covert communication.
Types of Steganography
Figure 1 shows the four main categories of file formats that can be used for steganography
Figure 1 Categories of steganography
Text: Hiding information in text is historically the most important method of steganography. An obvious method was to hide a secret message in every letter of every word of a text message. It is only since the beginning of the Internet and all the different digital file formats that is has decreased in importance. Text steganography using digital files is not used very often since text files have a very small amount of redundant data.
Image: Given the proliferation of digital images, especially on the Internet, and given the large amount of redundant bits present in the digital representation of an image, images are the most popular cover objects for steganography. This paper will focus on hiding information in images in the next sections.
Audio/Video: To hide information in audio files similar techniques are used as for image files. One different technique unique to audio steganography is masking, which exploits the properties of the human ear to hide information unnoticeably. A faint, but audible, sound becomes inaudible in the presence of another louder audible sound. This property creates a channel in which to hide information. Although nearly equal to images in steganographic potential, the larger size of meaningful audio files makes them less popular to use than images.
Protocol: The term protocol steganography refers to the technique of embedding information within messages and network control protocols used in network transmission. In the layers of the OSI network model there exist covert channels where steganography can be used. An example of where information can be hidden is in the header of a TCP/IP packet in some fields that are either optional or are never used.
 Muhalim Mohamed Amin “Information Hiding Using Steganography”, ethesis, Universiti Teknologi Malaysia, 2003.
 R. Popa,”An Analysis of Steganographic System”, The “Politehnica” University of Timisoara, Faculty of Automatics and Computers, Department of Computer Science and Software Engineering, May 25, 1998.
 Moerland, T., “Steganography and Steganalysis”, Leiden Institute of Advanced Computing Science, www.liacs.nl/home/tmoerl/privtech.pdf
 Artz, D., “Digital Steganography: Hiding Data within Data”, IEEE Internet Computing Journal, June 2001..