Steganography (/ˌstɛɡəˈnɒɡrəfi/ STEG-ə-NOG-rə-fee) is the practice of representing information within another message or physical object, in such a manner that the presence of the concealed information would not be evident to an unsuspecting person's examination. In computing/electronic contexts, a computer file, message, image, or video is concealed within another file, message, image, or video. Generally, the hidden messages appear to be (or to be part of) something else: images, articles, shopping lists, or some other cover text. For example, the hidden message may be in invisible ink between the visible lines of a private letter. Some implementations of steganography that lack a formal shared secret are forms of security through obscurity, while key-dependent steganographic schemes try to adhere to Kerckhoffs's principle.
The word steganography comes from Greek steganographia, which combines the words steganós (στεγανός), meaning "covered or concealed", and -graphia (γραφή) meaning "writing". 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 on magic.
