17-10-2017, 11:22 AM
The first recorded use of the term was in 1499 by Johannes Trithemius in his Steganographia, a treatise on cryptography and steganography, disguised as a book of magic. In general, hidden messages seem to be (or be part of) something else: pictures, articles, shopping lists, or some other cover story. For example, the hidden message may be in invisible ink between the visible lines of a private letter. Some steganography implementations lacking a shared secret are forms of security through obscurity, and key-dependent steganographic schemes adhere to the Kerckhoffs principle.
The advantage of steganography over cryptography alone is that the intended secret message does not attract attention to itself as an object of scrutiny. Clearly visible encrypted messages, no matter how unbreakable, arouse interest and can be incriminated in countries where encryption is illegal. While cryptography is the practice of protecting the content of a single message, steganography is concerned with hiding the fact that a secret message is sent and also conceals the message content.
Steganography includes concealment of information within computer files. In digital steganography, electronic communications may include steganographic coding within a transport layer, such as a document file, image file, program or protocol. Media files are ideal for steganography transmission because of its large size. For example, a sender could begin with an innocuous image file and adjust the colour of each hundredth pixel to match a letter of the alphabet. The change is so subtle that someone who is not specifically looking for it is unlikely to notice the change.