Steganography is one of the oldest arts that people have always wanted to have since they started communicating with each other, but sadly the least researched. Most people study steganography either as academic discipline or out of curiosity and I belong to the latter camp. Although steganography is used in military and commercial circuits the level of application and understanding is very low.
The term steganography as well cryptography was derived from the Greek language. The prefix crypto comes from the Greek word kryptos, which means hidden or secret bollinger bands. The suffix graphy was derived from graphia, which means writing. Cryptography is essentially the art of secret writing and the goal is to maintain the secrecy of the message even if it is visible. Steganography is also a form of writing (concealed writing). The Greek word steganos means unseen or hidden. Steganography is a form of hidden communication, it should not be seen as a replacement for cryptography but rather as a complement to it. Steganography, although closely related to cryptography, is different. The goal of cryptography is to conceal the content of a message, while the goal of steganography is to conceal the existence of a message. However, these two techniques can be combined effectively by first encrypting the secret message before embedding in a cover data. Concealing the transmission of encrypted messages enhances their overall security since outsiders are unaware of the communication.
Encrypted data can attract the attention of hackers and investigators through its mere existence, however if concealed, no attempt would be made to break the code or to obtain the secret key. Steganographic methods primarily use image or audio files to hide encrypted data, such techniques conceal information in the least significant bits of the carrier medium, which serves as a hiding place. It is important that the carrier medium does not lose its appearance after the embedding process.
Another technique similar to steganography is watermarking, the goal of watermarking is to mark an image or sound file to the owner by making elusive modifications to the file. These modifications should not be noticeable but rather, very robust; nobody should be able to remove an existing mark or mark an already marked file as belonging to him. This technique is of great interest to the entertainment industry because it gives an efficient way to determine if a file was illegally downloaded from the web or rightfully purchased.
A good steganography system should fulfil the same requirements posed by the Kerckhoff principle in cryptography that security of a system should not rely on the on its method of operation being unknown to the enemy, but rather on the choice of a secret key.
In recent years there has been an exciting convergence of information protection technologies and the main emphasis is information hiding as oppose to encryption. The two big policy issues of copyright protection and state surveillance motivated this development. The more information that is placed on the Internet or public media, the more the owner of the information need to protect themselves from theft and abuse. The entertainment industry is particularly very nervous due to the ease at which exact copies of digital music and video can be made. The way forward is to embrace advance technology to protect investment rather than oppose it. Part of the solution may be a change in the sale process of music and video; one mechanism is copyright marking (hiding notices and serial numbers in a way that would be difficult for pirates to remove). Systems and techniques that can uncover hidden information will be useful in computer forensics and digital traffic analysis. Understanding the limitations of current techniques can help develop more robust techniques. The principal focus is hiding information or at least stopping other people from hiding information.