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

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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