British Innovations and Discoveries. Steganography.

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 and 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.

The advantage of steganography over cryptography alone is that the intended secret message does not attract attention to itself as an object of scrutiny. Plainly visible encrypted messages, no matter how unbreakable they are, arouse interest and may in themselves be incriminating in countries in which encryption is illegal. Whereas cryptography is the practice of protecting the contents of a message alone, steganography is concerned with concealing both the fact that a secret message is being sent and its contents.

Steganography includes the concealment of information within computer files. In digital steganography, electronic communications may include steganographic coding inside a transport layer, such as a document file, image file, program, or protocol. Media files are ideal for steganographic transmission because of their large size. For example, a sender might start with an innocuous image file and adjust the color of every hundredth pixel to correspond to a letter in the alphabet. The change is so subtle that someone who is not looking for it is unlikely to notice the change.

History

A chart from Johannes Trithemius’s Steganographia copied by Dr John Dee in 1591
The first recorded uses of steganography can be traced back to 440 BC in Greece, when Herodotus mentions two examples in his Histories.[4] Histiaeus sent a message to his vassal, Aristagoras, by shaving the head of his most trusted servant, “marking” the message onto his scalp, then sending him on his way once his hair had regrown, with the instruction, “When thou art come to Miletus, bid Aristagoras shave thy head, and look thereon.” Additionally, Demaratus sent a warning about a forthcoming attack to Greece by writing it directly on the wooden backing of a wax tablet before applying its beeswax surface. Wax tablets were in common use then as reusable writing surfaces, sometimes used for shorthand.

In his work Polygraphiae, Johannes Trithemius developed his Ave Maria cipher that can hide information in a Latin praise of God.better source needed] “Auctor sapientissimus conseruans angelica deferat nobis charitas potentissimi creatoris”, for example, contains the concealed word VICIPEDIA.

Techniques

Main article: List of steganography techniques

A code chart from a transcription of Steganographia
Numerous techniques throughout history have been developed to embed a message within another medium.

Physical

Placing the message in a physical item has been widely used for centuries. Some notable examples include invisible ink on paper, writing a message in Morse code on yarn worn by a courier, microdots, or using a music cipher to hide messages as musical notes in sheet music.

Social steganography

In communities with social or government taboos or censorship, people use cultural steganography—hiding messages in idiom, pop culture references, and other messages they share publicly and assume are monitored. This relies on social context to make the underlying messages visible only to certain readers.Examples include:

Hiding a message in the title and context of a shared video or image.
Misspelling names or words that are popular in the media in a given week, to suggest an alternative meaning.
Hiding a picture that can be traced by using Paint or any other drawing tool.
Digital messages

Image of a tree with a steganographically hidden image. The hidden image is revealed by removing all but the two least significant bits of each color component and a subsequent normalization. The hidden image is shown below.

Since the dawn of computers, techniques have been developed to embed messages in digital cover mediums. The message to conceal is often encrypted, then used to overwrite part of a much larger block of encrypted data or a block of random data (an unbreakable cipher like the one-time pad generates ciphertexts that look perfectly random without the private key).

Examples of this include changing pixels in image or sound files, properties of digital text such as spacing and font choice, chaffing and winnowing, mimic functions, modifying the echo of a sound file (echo steganography)[citation needed], and including data in ignored sections of a file.