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 (ПѓП„ОµОіО±ОЅПЊП‚) acceptation "covered or protected", and graphei (ОіПЃО±П†О®) 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 abandoned 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.

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.

In his plan "Polygraphiae" Johannes Trithemius developed his alleged "Ave-Maria-Cipher" with which one can adumbrate advice in a Latin acclaim of God. "Auctor Sapientissimus Conseruans Angelica Deferat Nobis Charitas Potentissimi Creatoris" for archetype contains the buried chat VICIPEDIA.[3]

Techniques

Physical

Steganography has been broadly used, including in contempo actual times and the present day. Accessible 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 credible 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.

In the aboriginal canicule of the columnist press, it was accepted to mix altered typefaces on a printed page due to the printer not accepting abundant copies of some belletrist otherwise. So a bulletin could be hidden application 2 (or more) altered typefaces, such as accustomed or italic, on a page of type.

During Apple 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.

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

Jeremiah Denton again blinked his eyes in Morse Bare during the 1966 televised columnist appointment that he was affected into as an American POW by his North Vietnamese captors, spelling out the word, "T-O-R-T-U-R-E". This accepted for the aboriginal time to the U.S. Military (naval intelligence) and Americans that American POW's were getting bent in North Vietnam.

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

During and afterwards Apple 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. Apple War II microdots bare to be anchored in the cardboard and covered with an adhesive, such as collodion. This was cogitating and appropriately credible by examination adjoin casual light. Alternative techniques included inserting microdots into slits cut into the bend of column cards.

During WWII, Velvalee Dickinson, a spy for Japan in New York City, 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 abode 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 abode captivated as prisoners by North Korea, announced in assurance accent during staged photo opportunities, allegorical the United States they were not defectors, but were captives of the North Koreans. In added photos presented to the US, aggregation associates gave "the finger" to the biting North Koreans, in an advance to discredit photos that showed them animated and comfortable.

editDigital

This commodity needs absorption from an able in History of Science. Please add a acumen or a allocution constant to this arrangement to explain the affair with the article. WikiProject History of Science or the History of Science Portal may be able to advice recruit an expert. (May 2008)

Image of a timberline with a steganographically hidden image. The hidden angel is appear by removing all but the two atomic cogent $.25 of anniversary blush basal and a consecutive normalization. The hidden angel is credible below.

Image of a cat extracted from the timberline angel above.

Modern steganography entered the apple in 1985 with the appearance of the claimed computer getting activated to classical steganography problems.4 Development afterward that was slow, but has back taken off, traveling by the amount of "stego" programs available:

Concealing belletrist aural the everyman $.25 of blatant images or complete files.

Concealing abstracts aural encrypted abstracts or aural accidental data. The abstracts to be buried are aboriginal encrypted afore getting acclimated to overwrite allotment of a abundant beyond block of encrypted abstracts or a block of accidental abstracts (an adamantine bare like the ancient pad generates ciphertexts that attending altogether accidental if one does not accept the clandestine key).

Chaffing and winnowing.

Mimic functions catechumen one book to accept the statistical contour of another. This can baffle statistical methods that advice brute-force attacks analyze the appropriate band-aid in a ciphertext-only attack.

Concealed belletrist in tampered executable files, base back-up in the targeted apprenticeship set.

Pictures anchored in video actual (optionally played at slower or faster speed).

Injecting ephemeral delays to packets beatific over the arrangement from the keyboard. Delays in keypresses in some applications (telnet or limited desktop software) can beggarly a adjournment in packets, and the delays in the packets can be acclimated to encode data.

Changing the adjustment of elements in a set.

Content-Aware Steganography hides advice in the semantics a animal user assigns to a datagram. These systems action aegis adjoin a non-human adversary/warden.

Blog-Steganography. Belletrist are fractionalized and the (encrypted) pieces are added as comments of orphaned web-logs (or pin boards on amusing arrangement platforms). In this case the alternative of blogs is the symmetric key that sender and almsman are using; the carrier of the hidden bulletin is the accomplished blogosphere.

Modifying the answer of a complete book (Echo Steganography).5

Secure Steganography for Audio Signals.6

Image bit-plane complication analysis steganography

Including abstracts in abandoned sections of a file, such as afterwards the analytic end of the carrier file.

editNetwork

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 2003.7 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.8

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),91011 to the time relations amid the exchanged PDUs,12 or both (hybrid methods).13

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.14

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

Steganophony - the beard of belletrist 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.15

WLAN Steganography – the appliance of methods that may be acclimatized to abode steganograms in Wireless Local Breadth Networks. A applied archetype of WLAN Steganography is the HICCUPS arrangement (Hidden Advice Arrangement for Besmirched Networks)16

editPrinted

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 afresh break it. Francis Bacon developed Bacon's bare 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 accept to be transmitted to the almsman with no added babble from the transmission. Columnist 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.17

editDigital Text

Unicode steganography uses lookalike characters of the accepted ASCII set to attending normal, while absolutely accustomed added $.25 of information. If the argument is displayed correctly, there should be no beheld aberration from accustomed text. Some systems, however, may affectation the fonts differently, and the added advice would be calmly spotted.

Alternately, hidden (e.g., control) characters, and bombastic use of markup (e.g., abandoned bold, accentuate or italics) can add anchored aural a physique of argument to adumbrate advice that wouldn't be visually credible if displayed, but can be apparent by analytical the certificate source. HTML pages can accommodate bare for added bare spaces and tabs at the end of lines, as able-bodied as altered colours, fonts and sizes, which will not be arresting if displayed. A added atomic archetype is white argument on a white background, which can be appear by "selecting".

One such adjustment is based on the non-printing Unicode characters Zero-Width Joiner (ZWJ) and Zero-Width Non-Joiner (ZWNJ).18 These characters are acclimated for abutting and disengagement belletrist in Arabic, but can be acclimated in Roman alphabets for ambuscade advice because they accept no acceptation in Roman alphabets, and because they are "zero-width" and appropriately not displayed. The embedding of ZWJ in the cover-text represents “1” and the embedding of ZWNJ represents “0”. Groups of characters can be acclimated to represent the belletrist A (giving it the bare “0”, and appropriately represented by ZWNJ) to Z (giving it the bare “1011”, and appropriately represented by ZWJ,ZWNJ,ZWJ,ZWJ). These appearance groups can be amid amid anniversary appearance of the cover-text, thereby ambuscade a message.

editUsing Sudoku puzzles

This is the art of concealing abstracts in an angel application Sudoku which is acclimated like a key to adumbrate the abstracts aural an image. Steganography application sudoku puzzles has as abounding keys as there are accessible solutions of a Sudoku puzzle, which is 6.71Г—1021. This is agnate to about 70 bits, authoritative it abundant stronger than the DES adjustment which uses a 56 bit key.19

Data embedding security schemes

The best of embedding algorithm in the a lot of cases is apprenticed by the after-effects of the steganographic access robustness assay . One of the areas that improves steganographic robustness is acceptance of a key arrangement for embedding messages.20 Assorted key steganographic schemes accept assorted levels of protection. Key arrangement appellation agency a action of how to use key steganographic arrangement based on the admeasurement of its use. However, if the steganographic robustness is added a bandwidth of the accomplished embedding arrangement is decreased. Therefore the assignment of a arrangement alternative for accomplishing the optimal ethics of the steganographic arrangement is not trivial.

Embedding letters in steganographic arrangement can be agitated out after use of a key or with use of a key. To advance steganographic robustness key can be acclimated as a analysis option. It can accomplish an appulse on the administration of $.25 of a bulletin aural a container, as able-bodied as an appulse on the action of basic a arrangement of anchored $.25 of a message.

The aboriginal akin of aegis is bent alone by the best of embedding algorithm. This may be the atomic cogent $.25 modification algorithm, or algorithms for modifying the abundance or spatial-temporal characteristics of the container. The aboriginal akin of aegis is presented in any steganographic channel. Steganographic arrangement in this case can be represented as apparent at The Aboriginal Aegis Akin Arrangement figure. There afterward notations are used: c - is a alembic file; F - steganographic access amplitude (frequency or/and amplitude alembic part, that is accessible for steganographic modification and bulletin arresting transmission); SC - steganographic system; m - bulletin to be embedded; E - embedding method; Д‰ - adapted alembic file.

The additional aegis akin of the steganographic system, as able-bodied as all levels of aegis of the college orders, is characterized by the use of Key (password) via steganographic modification. An archetype of a simple key scheme, which provides a additional akin of protection, is to address the blunt or adapted countersign in the top or basal of the message; or the administration of the countersign assurance on the absolute breadth of the steganographic channel. Such key schemes do not affect the administration of letters through the alembic and do not use a bulletin preprocessing according to the authentic key (see amount The Additional Aegis Akin Scheme). This affectionate of steganographic systems are acclimated in such tasks as, for instance, abacus a agenda signature for affidavit of copyright. Abstracts embedding achievement is not afflicted in allegory with the fastest access of the aboriginal aegis akin usage.

Steganographic abstracts channels that use key schemes based administration of a bulletin through the alembic and or preprocessing of an anchored bulletin for abstracts ambuscade are added secure. If the third aegis akin key arrangement is acclimated it affects the administration of a bulletin through the alembic (see amount The Third Aegis Akin Scheme, area F(P, L) – administration action of a bulletin aural a container; P – minimum amount of alembic samples that are bare to bury one bulletin sample; L – footfall of a bulletin administration aural a container). Accordingly, the achievement of alembic processing will be lower than in the case of the aboriginal and the additional key schemes. Taking into annual that P≥L, the simplest representation of the F(P, L) action could be as following:

F(P, L) = cycle*L + step*P,

where aeon is a amount of the accepted L area and footfall is a amount of the anchored bulletin sample.

The aberration amid the fourth aegis akin arrangement and the third one is that in steganographic arrangement there are two administration functions of a bulletin aural a alembic are used. The aboriginal is amenable for a bulletin samples alternative according to some action G(Q, N), and the additional action F(P, L) is amenable for position alternative in a alembic for bulletin sample hiding. Here Q – the admeasurement of bulletin block to be inserted; N – the admeasurement (in bits) of one sample of the bulletin book (see amount The Fourth Aegis Akin Scheme).

Based on the aloft altercation it is accessible to ascertain a allocation table of key steganographic schemes:

Key Steganographic Schemes Classification

Steganographic arrangement aegis level Steganographic algorithm usage Key (password) usage Key access on a bulletin arresting $.25 administration per container Key access on a bulletin arresting $.25 alternative and administration per container

1 + - - -

2 + + - -

3 + + + -

4 + + + +

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).

Applications

Usage in avant-garde printers

Main article: Printer steganography

Steganography is acclimated by some avant-garde printers, including HP and Xerox cast blush laser printers. Tiny chicken dots are added to anniversary page. The dots are almost arresting and accommodate encoded printer consecutive numbers, as able-bodied as date and time stamps.21

editExample from avant-garde practice

The beyond the awning bulletin is (in abstracts agreeable terms—number of bits) about to the hidden message, the easier it is to adumbrate the latter. For this reason, agenda pictures (which accommodate ample amounts of data) are acclimated to adumbrate letters on the Internet and on added advice media. It is not bright how frequently this is in fact done. For example: a 24-bit bitmap will accept 8 $.25 apery anniversary of the three blush ethics (red, green, and blue) at anniversary pixel. If we accede just the dejected there will be 28 altered ethics of blue. The aberration amid 11111111 and 11111110 in the bulk for dejected acuteness is acceptable to be ephemeral by the animal eye. Therefore, the atomic cogent bit can be acclimated (more or beneath undetectably) for something away added than blush information. If we do it with the blooming and the red as able-bodied we can get one letter of ASCII argument for every three pixels.

Stated somewhat added formally, the cold for authoritative steganographic encoding difficult to ascertain is to ensure that the changes to the carrier (the aboriginal signal) due to the bang of the burden (the arresting to covertly embed) are visually (and ideally, statistically) negligible; that is to say, the changes are duplicate from the babble attic of the carrier. Any average can be a carrier, but media with a ample bulk of bombastic or compressible advice are bigger suited.

From an advice abstract point of view, this agency that the access accept to accept added accommodation than the "surface" arresting requires; that is, there accept to be redundancy. For a agenda image, this may be babble from the imaging element; for agenda audio, it may be babble from recording techniques or accession equipment. In general, electronics that digitize an analog arresting ache from several babble sources such as thermal noise, beam noise, and attempt noise. This babble provides abundant aberration in the captured agenda advice that it can be exploited as a babble awning for hidden data. In addition, lossy compression schemes (such as JPEG) consistently acquaint some absurdity into the decompressed data; it is accessible to accomplishment this for steganographic use as well.

Steganography can be acclimated for agenda watermarking, area a bulletin (being artlessly an identifier) is hidden in an angel so that its antecedent can be tracked or absolute (for example, Coded Anti-Piracy), or even just to analyze an angel (as in the EURion constellation).

editUse by terrorists

When one considers that letters could be encrypted steganographically in e-mail messages, decidedly e-mail spam, the angle of clutter e-mail takes on a accomplished new light. Coupled with the "chaffing and winnowing" technique, a sender could get letters out and awning their advance all at once.

An archetype assuming how terrorists may use appointment avatars to forward hidden messages. This avatar contains the bulletin "Boss said that we should draft up the arch at midnight." encrypted with mozaiq appliance "växjö" as password.

Rumors about terrorists appliance steganography started aboriginal in the circadian bi-weekly USA Today on February 5, 2001 in two online writing blue-blooded "Terrorist instructions hidden online" and "Terror groups adumbrate abaft Web encryption". In July the aforementioned year, an commodity was blue-blooded even added precisely: "Militants wire Web with links to jihad". A commendation from the article: "Lately, al-Qaeda agents accept been sending hundreds of encrypted letters that accept been hidden in files on agenda photographs on the bargain website eBay.com". Added media common cited these rumors abounding times, abnormally afterwards the agitator advance of 9/11, afterwards anytime assuming proof. The Italian bi-weekly Corriere della Sera appear that an Al Qaeda corpuscle which had been captured at the Via Quaranta abbey in Milan had pornographic images on their computers, and that these images had been acclimated to adumbrate abstruse letters (although no added Italian cardboard anytime covered the story). The USA Today online writing were accounting by adept adopted contributor Jack Kelley, who in 2004 was accursed afterwards allegations emerged that he had bogus belief and sources.

In October 2001, the New York Times appear an commodity claiming that al-Qaeda had acclimated steganography to encode letters into images, and again transported these via e-mail and possibly via USENET to adapt and assassinate the September 11, 2001 agitator attack. The Federal Plan for Cyber Aegis and Advice Assurance Research and Development,22 appear in April 2006 makes the afterward statements:

"...immediate apropos aswell awning the use of cyberspace for buried communications, decidedly by terrorists but aswell by adopted intelligence services; espionage adjoin acute but ailing dedicated abstracts in government and industry systems; abolishment by insiders, including vendors and contractors; bent activity, primarily involving artifice and annexation of banking or character information, by hackers and organized abomination groups..." (p. 9–10)

"International absorption in R&D for steganography technologies and their commercialization and appliance has exploded in contempo years. These technologies affectation a abeyant blackmail to civic security. Because steganography secretly embeds additional, and about undetectable, advice agreeable in agenda products, the abeyant for buried broadcasting of awful software, adaptable code, or advice is great." (p. 41–42)

"The blackmail airish by steganography has been accurate in abundant intelligence reports." (p. 42)

Moreover, an online "terrorist training manual", the "Technical Mujahid, a Training Manual for Jihadis" independent a area advantaged "Covert Communications and Hiding Secrets Central Images."23

By aboriginal 2002, a Cranfield University MSc apriorism developed the aboriginal applied accomplishing of an online real-time Counter Agitator Steganography Search Engine. This was advised to ascertain the a lot of acceptable angel steganography in alteration and thereby accommodate UK Ministry of Defence Intelligence Staff a astute access to "narrowing the field", suggesting that interception accommodation was never the adversity but rather prioritising the ambition media.

According to afresh begin material, hidden letters from Al-Qaeda were begin in a backing of pornography.24

editAlleged use by intelligence services

In 2010, the Federal Bureau of Investigation appear that the Russian adopted intelligence account uses customized steganography software for embedding encrypted argument letters central angel files for assertive communications with "illegal agents" (agents beneath non-diplomatic cover) stationed abroad.25