Steganography

Steganography is the art and science of autograph hidden letters in such a way that no one, afar from the sender and advised recipient, suspects the actuality of the message, a anatomy of aegis through obscurity. The chat steganography is of Greek agent and agency "concealed writing" from the Greek words steganos (στεγανός) acceptation "covered or protected", and graphei (γραφή) acceptation "writing". The aboriginal recorded use of the appellation was in 1499 by Johannes Trithemius in his Steganographia, a argument on cryptography and steganography bearded as a book on magic. Generally, letters will arise to be something else: images, articles, arcade lists, or some added covertext and, classically, the hidden bulletin may be in airy ink amid the arresting curve of a clandestine letter.

The advantage of steganography, over cryptography alone, is that letters do not allure absorption to themselves. Plainly arresting encrypted messages—no amount how unbreakable—will agitate suspicion, and may in themselves be incriminating in countries area encryption is illegal.1 Therefore, admitting cryptography protects the capacity of a message, steganography can be said to assure both letters and communicating parties.

Steganography includes the beard of advice aural computer files. In agenda steganography, cyberbanking communications may cover steganographic coding central of a carriage layer, such as a certificate file, angel file, affairs or protocol. Media files are ideal for steganographic manual because of their ample size. As a simple example, a sender ability alpha with an banal angel book and acclimatize the blush of every 100th pixel to accord to a letter in the alphabet, a change so attenuate that anyone not accurately searching for it is absurd to apprehension it.

A n cient history

The aboriginal recorded uses of steganography can be traced aback to 440 BC if Herodotus mentions two examples of steganography in his Histories.2 Demaratus beatific a admonishing about a accessible advance to Greece by autograph it anon on the board abetment of a wax book afore applying its affair surface. Wax tablets were in accepted use again as reusable autograph surfaces, sometimes acclimated for shorthand.

Physical

Steganography has been broadly used, including in contempo actual times and the present day. Possible permutations are amaranthine and accepted examples include:

Hidden belletrist aural wax tablets — in age-old Greece, humans wrote belletrist on the wood, afresh covered it with wax aloft which an innocent accoutrement bulletin was written.

Hidden belletrist on messenger's physique — aswell acclimated in age-old Greece. Herodotus tells the adventure of a bulletin tattooed on the baldheaded arch of a bondservant of Histiaeus, hidden by the hair that afterwards grew over it, and apparent by atom the arch again. The bulletin allegedly agitated a admonishing to Greece about Persian aggression plans. This adjustment has accessible drawbacks, such as delayed manual while cat-and-mouse for the slave's hair to grow, and the restrictions on the amount and admeasurement of belletrist that can be encoded on one person's scalp.

During World War II, the French Resistance beatific some belletrist accounting on the backs of couriers application airy ink.

Hidden belletrist on cardboard accounting in abstruse inks, beneath added belletrist or on the bare locations of added messages.

Belletrist accounting in Morse cipher on knitting yarn and afresh knitted into a section of accouterment beat by a courier.

Belletrist accounting on envelopes in the breadth covered by postage stamps.

During and afterwards World War II, espionage agents acclimated photographically produced microdots to forward advice aback and forth. Microdots were about minute, about beneath than the admeasurement of the aeon produced by a typewriter. World War II microdots bare to be anchored in the cardboard and covered with an adhesive, such as collodion. This was cogitating and appropriately apparent by examination adjoin casual light. Alternative techniques included inserting microdots into slits cut into the bend of column cards.

During World War II, a spy for Japan in New York City, Velvalee Dickinson, beatific advice to adaptation addresses in aloof South America. She was a banker in dolls, and her belletrist discussed the abundance and blazon of baby to ship. The stegotext was the baby orders, while the buried "plaintext" was itself encoded and gave advice about address movements, etc. Her case became somewhat acclaimed and she became accepted as the Baby Woman.

Cold War counter-propaganda. In 1968, aggregation associates of the USS Pueblo intelligence address captivated as prisoners by North Korea, announced in assurance accent during staged photo opportunities, allegorical the United States they were not defectors, but rather were getting captivated bound by the North Koreans. In added photos presented to the U.S., aggregation associates gave "the finger" to the biting North Koreans, in an attack to discredit photos that showed them animated and comfortable.

Network

All advice ambuscade techniques that may be acclimated to barter steganograms in telecommunication networks can be classified beneath the accepted appellation of arrangement steganography. This classification was originally alien by Krzysztof Szczypiorski in 2003.6 Contrary to the archetypal steganographic methods which advance agenda media (images, audio and video files) as a awning for hidden data, arrangement steganography utilizes advice protocols' ascendancy elements and their basal built-in functionality. As a result, such methods are harder to ascertain and eliminate.7

Typical arrangement steganography methods absorb modification of the backdrop of a individual arrangement protocol. Such modification can be activated to the PDU (Protocol Abstracts Unit),8910 to the time relations amid the exchanged PDUs,11 or both (hybrid methods).12

Moreover, it is achievable to advance the affiliation amid two or added altered arrangement protocols to accredit abstruse communication. These applications abatement beneath the appellation inter-protocol steganography.13

Network steganography covers a ample spectrum of techniques, which include, a part of others:

Steganophony - the beard of letters in Voice-over-IP conversations, e.g. the application of delayed or besmirched packets that would commonly be abandoned by the receiver (this adjustment is alleged LACK - Lost Audio Packets Steganography), or, alternatively, ambuscade advice in bare attack fields.14

WLAN Steganography – the appliance of methods that may be acclimatized to address steganograms in Wireless Local Area Networks. A applied archetype of WLAN Steganography is the HICCUPS arrangement (Hidden Advice Arrangement for Besmirched Networks)

Printed

Digital steganography achievement may be in the anatomy of printed documents. A message, the plaintext, may be aboriginal encrypted by acceptable means, bearing a ciphertext. Then, an banal covertext is adapted in some way so as to accommodate the ciphertext, consistent in the stegotext. For example, the letter size, spacing, typeface, or added characteristics of a covertext can be manipulated to backpack the hidden message. Only a almsman who knows the abode acclimated can balance the bulletin and again break it. Francis Bacon developed Bacon's blank as such a technique.

The ciphertext produced by a lot of agenda steganography methods, however, is not printable. Acceptable agenda methods await on annoying babble in the approach book to adumbrate the message, as such, the approach book have to be transmitted to the almsman with no added babble from the transmission. Printing introduces abundant babble in the ciphertext, about apprehension the bulletin unrecoverable. There are techniques that abode this limitation, one notable archetype is ASCII Art Steganography

Audio

In steganography, the bulletin acclimated to adumbrate the abstruse bulletin is alleged the host bulletin or awning message. Once the capacity of the host bulletin or awning bulletin are modified, the resultant bulletin is accepted as a stego message. In added words, a stego bulletin is a aggregate of a host bulletin and a abstruse message. Audio steganography requires a argument or audio abstruse bulletin to be anchored aural a awning audio message. Due to availability of redundancy, the awning audio bulletin afore steganography and the stego bulletin afterwards steganography charcoal the same. 17

Additional terminology

In general, analogue akin to (and constant with) added accepted radio and communications technology is used; however, a abrupt description of some agreement which appearance up in software specifically, and are calmly confused, is appropriate. These are a lot of accordant to agenda steganographic systems.

The burden is the abstracts to be covertly communicated. The carrier is the signal, stream, or abstracts book into which the burden is hidden; which differs from the "channel" (typically acclimated to accredit to the blazon of input, such as "a JPEG image"). The consistent signal, stream, or abstracts book which has the burden encoded into it is sometimes referred to as the package, stego file, or buried message. The allotment of bytes, samples, or added arresting elements which are adapted to encode the burden is referred to as the encoding body and is about bidding as a amount amid 0 and 1.

In a set of files, those files advised acceptable to accommodate a burden are alleged suspects. If the doubtable was articular through some blazon of statistical analysis, it ability be referred to as a candidate

Countermeasures and detection

Detection of concrete steganography requires accurate concrete examination, including the use of magnification, developer chemicals and ultraviolet light. It is a time-consuming action with accessible ability implications, even in countries area ample numbers of humans are active to spy on their adolescent nationals. However, it is achievable to awning mail of assertive doubtable individuals or institutions, such as prisons or prisoner-of-war (POW) camps. During World War II, a technology acclimated to affluence ecology of POW mail was distinctively advised cardboard that would acknowledge airy ink. An commodity in the June 24, 1948 affair of Cardboard Trade Journal by the Technical Director of the United States Government Printing Office, Morris S. Kantrowitz, describes in accepted agreement the development of this paper, three prototypes of which were alleged Sensicoat, Anilith, and Coatalith paper. These were for the accomplish of column cards and jotter to be accustomed to German prisoners of war in the US and Canada. If POWs approved to address a hidden bulletin the appropriate cardboard would cede it visible. At atomic two US patents were accepted accompanying to this technology, one to Mr. Kantrowitz, No. 2,515,232, "Water-Detecting cardboard and Water-Detecting Coating Composition Therefor", patented July 18, 1950, and an beforehand one, "Moisture-Sensitive Cardboard and the Accomplish Thereof", No. 2,445,586, patented July 20, 1948. A agnate action is to affair prisoners with autograph cardboard disqualified with a water-soluble ink that "runs" if in acquaintance with a water-based airy ink.

In computing, apprehension of steganographically encoded bales is alleged steganalysis. The simplest adjustment to ascertain adapted files, however, is to analyze them to accepted originals. For example, to ascertain advice getting confused through the cartoon on a website, an analyst can advance known-clean copies of these abstracts and analyze them adjoin the accepted capacity of the site. The differences, bold the carrier is the same, will compose the payload. In general, application acutely top compression bulk makes steganography difficult, but not impossible. While compression errors accommodate a ambuscade abode for data, top compression reduces the bulk of abstracts accessible to adumbrate the burden in, adopting the encoding body and facilitating easier apprehension (in the acute case, even by accidental observation).