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82-587: Steganographia is a book on steganography , written in c. 1499 by the German Benedictine abbot and polymath Johannes Trithemius . Trithemius' most famous work, Steganographia (written c.1499; published Frankfurt , 1606), was placed on the Index Librorum Prohibitorum in 1609 and removed in 1900. This book is in three volumes, and appears to be about magic —specifically, about using spirits to communicate over long distances. However, since

164-412: A native resolution , and it should (ideally) be matched to the video card resolution. Each pixel is made up of triads , with the number of these triads determining the native resolution. On older, historically available, CRT monitors the resolution was possibly adjustable (still lower than what modern monitor achieve), while on some such monitors (or TV sets) the beam sweep rate was fixed, resulting in

246-545: A regular two-dimensional grid . By using this arrangement, many common operations can be implemented by uniformly applying the same operation to each pixel independently. Other arrangements of pixels are possible, with some sampling patterns even changing the shape (or kernel ) of each pixel across the image. For this reason, care must be taken when acquiring an image on one device and displaying it on another, or when converting image data from one pixel format to another. For example: Computer monitors (and TV sets) generally have

328-413: 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 so-called " Ave-Maria-Cipher " that can hide information in a Latin praise of God. " Auctor Sapientissimus Conseruans Angelica Deferat Nobis Charitas Potentissimi Creatoris " for example contains

410-548: A "pixel" may refer to a fixed length rather than a true pixel on the screen to accommodate different pixel densities . A typical definition, such as in CSS , is that a "physical" pixel is 1 ⁄ 96 inch (0.26 mm). Doing so makes sure a given element will display as the same size no matter what screen resolution views it. There may, however, be some further adjustments between a "physical" pixel and an on-screen logical pixel. As screens are viewed at difference distances (consider

492-420: A 1200 dpi inkjet printer. Even higher dpi numbers, such as the 4800 dpi quoted by printer manufacturers since 2002, do not mean much in terms of achievable resolution . The more pixels used to represent an image, the closer the result can resemble the original. The number of pixels in an image is sometimes called the resolution, though resolution has a more specific definition. Pixel counts can be expressed as

574-429: A 24-bit bitmap uses 8 bits to represent each of the three color values (red, green, and blue) of each pixel . The blue alone has 2 different levels of blue intensity. The difference between 11111111 and 11111110 in the value for blue intensity is likely to be undetectable by the human eye. Therefore, the least significant bit can be used more or less undetectably for something else other than color information. If that

656-415: A cover text can be manipulated to carry the hidden message. Only a recipient who knows the technique used can recover the message and then decrypt it. Francis Bacon developed Bacon's cipher as such a technique. The ciphertext produced by most digital steganography methods, however, is not printable. Traditional digital methods rely on perturbing noise in the channel file to hide the message, and as such,

738-412: A data hiding technique leading to compressed forms of source video signals on a frame-by-frame basis. In 2005, Dittmann et al. studied steganography and watermarking of multimedia contents such as VoIP. In 2008, Yongfeng Huang and Shanyu Tang presented a novel approach to information hiding in low bit-rate VoIP speech stream, and their published work on steganography is the first-ever effort to improve

820-466: A distance. In some displays, such as LCD, LED, and plasma displays, these single-color regions are separately addressable elements, which have come to be known as subpixels , mostly RGB colors. For example, LCDs typically divide each pixel vertically into three subpixels. When the square pixel is divided into three subpixels, each subpixel is necessarily rectangular. In display industry terminology, subpixels are often referred to as pixels , as they are

902-609: 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 specifically looking for it is unlikely to notice the change. The first recorded uses of steganography can be traced back to 440 BC in Greece , when Herodotus mentions two examples in his Histories . Histiaeus sent

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984-484: A dot-matrix code made of small, yellow dots not recognizable to the naked eye — see printer steganography for details. In 2015, a taxonomy of 109 network hiding methods was presented by Steffen Wendzel, Sebastian Zander et al. that summarized core concepts used in network steganography research. The taxonomy was developed further in recent years by several publications and authors and adjusted to new domains, such as CPS steganography. In 1977, Kent concisely described

1066-450: A fixed native resolution . What it is depends on the monitor, and size. See below for historical exceptions. Computers can use pixels to display an image, often an abstract image that represents a GUI . The resolution of this image is called the display resolution and is determined by the video card of the computer. Flat-panel monitors (and TV sets), e.g. OLED or LCD monitors, or E-ink , also use pixels to display an image, and have

1148-426: A fixed native resolution. Most CRT monitors do not have a fixed beam sweep rate, meaning they do not have a native resolution at all – instead they have a set of resolutions that are equally well supported. To produce the sharpest images possible on an flat-panel, e.g. OLED or LCD, the user must ensure the display resolution of the computer matches the native resolution of the monitor. The pixel scale used in astronomy

1230-522: A hidden message, the special paper rendered it visible. The US granted at least two patents related to the technology, one to Kantrowitz, U.S. patent 2,515,232 , "Water-Detecting paper and Water-Detecting Coating Composition Therefor," patented 18 July 1950, and an earlier one, "Moisture-Sensitive Paper and the Manufacture Thereof," U.S. patent 2,445,586 , patented 20 July 1948. A similar strategy issues prisoners with writing paper ruled with

1312-789: A manner that is both less detectable and more robust across various facial orientations within images. This strategy can potentially improve the efficacy of information hiding in both static images and video content. Academic work since 2012 demonstrated the feasibility of steganography for cyber-physical systems (CPS)/the Internet of Things (IoT). Some techniques of CPS/IoT steganography overlap with network steganography, i.e. hiding data in communication protocols used in CPS/the IoT. However, specific techniques hide data in CPS components. For instance, data can be stored in unused registers of IoT/CPS components and in

1394-453: A measured intensity level. In most digital cameras, the sensor array is covered with a patterned color filter mosaic having red, green, and blue regions in the Bayer filter arrangement so that each sensor element can record the intensity of a single primary color of light. The camera interpolates the color information of neighboring sensor elements, through a process called demosaicing , to create

1476-487: A message (being simply an identifier) is hidden in an image so that its source can be tracked or verified (for example, Coded Anti-Piracy ) or even just to identify an image (as in the EURion constellation ). In such a case, the technique of hiding the message (here, the watermark) must be robust to prevent tampering. However, digital watermarking sometimes requires a brittle watermark, which can be modified easily, to check whether

1558-412: 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

1640-600: A new framework for reconstructing lost or corrupted audio signals using a combination of machine learning techniques and latent information. The main idea of their paper is to enhance audio signal reconstruction by fusing steganography, halftoning (dithering), and state-of-the-art shallow and deep learning methods (e.g., RF, LSTM). This combination of steganography, halftoning, and machine learning for audio signal reconstruction may inspire further research in optimizing this approach or applying it to other domains, such as image reconstruction (i.e., inpainting). Adaptive steganography

1722-406: A particular algorithm has much better success as it is able to key in on the anomalies that are left behind. This is because the analysis can perform a targeted search to discover known tendencies since it is aware of the behaviors that it commonly exhibits. When analyzing an image the least significant bits of many images are actually not random. The camera sensor, especially lower-end sensors are not

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1804-471: A phone, a computer display, and a TV), the desired length (a "reference pixel") is scaled relative to a reference viewing distance (28 inches (71 cm) in CSS). In addition, as true screen pixel densities are rarely multiples of 96 dpi, some rounding is often applied so that a logical pixel is an integer amount of actual pixels. Doing so avoids render artifacts. The final "pixel" obtained after these two steps becomes

1886-481: A result, such methods can be harder to detect and eliminate. Typical network steganography methods involve modification of the properties of a single network protocol. Such modification can be applied to the protocol data unit (PDU), to the time relations between the exchanged PDUs, or both (hybrid methods). Moreover, it is feasible to utilize the relation between two or more different network protocols to enable secret communication. These applications fall under

1968-419: A single number, as in a "three-megapixel" digital camera, which has a nominal three million pixels, or as a pair of numbers, as in a "640 by 480 display", which has 640 pixels from side to side and 480 from top to bottom (as in a VGA display) and therefore has a total number of 640 × 480 = 307,200 pixels, or 0.3 megapixels. The pixels, or color samples, that form a digitized image (such as a JPEG file used on

2050-403: A single scalar element of a multi-component representation (called a photosite in the camera sensor context, although sensel ' sensor element ' is sometimes used), while in yet other contexts (like MRI) it may refer to a set of component intensities for a spatial position. Software on early consumer computers was necessarily rendered at a low resolution, with large pixels visible to

2132-426: A unit of measure such as: 2400 pixels per inch, 640 pixels per line, or spaced 10 pixels apart. The measures " dots per inch " (dpi) and " pixels per inch " (ppi) are sometimes used interchangeably, but have distinct meanings, especially for printer devices, where dpi is a measure of the printer's density of dot (e.g. ink droplet) placement. For example, a high-quality photographic image may be printed with 600 ppi on

2214-586: A variety of basic tests that can be done to identify whether or not a secret message exists. This process is not concerned with the extraction of the message, which is a different process and a separate step. The most basic approaches of steganalysis are visual or aural attacks, structural attacks, and statistical attacks. These approaches attempt to detect the steganographic algorithms that were used. These algorithms range from unsophisticated to very sophisticated, with early algorithms being much easier to detect due to statistical anomalies that were present. The size of

2296-425: A water-soluble ink that runs in contact with water-based invisible ink. In computing, steganographically encoded package detection is called steganalysis . The simplest method to detect modified files, however, is to compare them to known originals. For example, to detect information being moved through the graphics on a website, an analyst can maintain known clean copies of the materials and then compare them against

2378-432: A web page) may or may not be in one-to-one correspondence with screen pixels, depending on how a computer displays an image. In computing, an image composed of pixels is known as a bitmapped image or a raster image . The word raster originates from television scanning patterns, and has been widely used to describe similar halftone printing and storage techniques. For convenience, pixels are normally arranged in

2460-406: Is a sample of an original image; more samples typically provide more accurate representations of the original. The intensity of each pixel is variable. In color imaging systems, a color is typically represented by three or four component intensities such as red, green, and blue , or cyan, magenta, yellow, and black . In some contexts (such as descriptions of camera sensors ), pixel refers to

2542-468: Is a technique for concealing information within digital media by tailoring the embedding process to the specific features of the cover medium. An example of this approach is demonstrated in the work. Their method develops a skin tone detection algorithm, capable of identifying facial features, which is then applied to adaptive steganography. By incorporating face rotation into their approach, the technique aims to enhance its adaptivity to conceal information in

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2624-413: Is a time-consuming process with obvious resource implications, even in countries that employ many people to spy on their fellow nationals. However, it is feasible to screen mail of certain suspected individuals or institutions, such as prisons or prisoner-of-war (POW) camps. During World War II , prisoner of war camps gave prisoners specially-treated paper that would reveal invisible ink . An article in

2706-403: Is available: this means that each 24-bit pixel has an extra 8 bits to describe its opacity (for purposes of combining with another image). Many display and image-acquisition systems are not capable of displaying or sensing the different color channels at the same site. Therefore, the pixel grid is divided into single-color regions that contribute to the displayed or sensed color when viewed at

2788-488: Is challenging, and because of that, not an adequate defence. Therefore, the only way of defeating the threat is to transform data in a way that destroys any hidden messages, a process called Content Threat Removal . Some modern computer printers use steganography, including Hewlett-Packard and Xerox brand color laser printers. The printers add tiny yellow dots to each page. The barely-visible dots contain encoded printer serial numbers and date and time stamps. The larger

2870-485: Is generally thought of as the smallest single component of a digital image . However, the definition is highly context-sensitive. For example, there can be " printed pixels " in a page, or pixels carried by electronic signals, or represented by digital values, or pixels on a display device, or pixels in a digital camera (photosensor elements). This list is not exhaustive and, depending on context, synonyms include pel, sample, byte, bit, dot, and spot. Pixels can be used as

2952-411: 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 of a transport layer, such as

3034-438: Is not possible to reliably distinguish data containing a hidden message from data containing just noise—even when the most sophisticated analysis is performed. Steganography is being used to conceal and deliver more effective cyber attacks, referred to as Stegware . The term Stegware was first introduced in 2017 to describe any malicious operation involving steganography as a vehicle to conceal an attack. Detection of steganography

3116-480: Is repeated for the green and the red elements of each pixel as well, it is possible to encode one letter of ASCII text for every three pixels . Stated somewhat more formally, the objective for making steganographic encoding difficult to detect is to ensure that the changes to the carrier (the original signal) because of the injection of the payload (the signal to covertly embed) are visually (and ideally, statistically) negligible. The changes are indistinguishable from

3198-630: Is the angular distance between two objects on the sky that fall one pixel apart on the detector (CCD or infrared chip). The scale s measured in radians is the ratio of the pixel spacing p and focal length f of the preceding optics, s = p / f . (The focal length is the product of the focal ratio by the diameter of the associated lens or mirror.) Because s is usually expressed in units of arcseconds per pixel, because 1 radian equals (180/π) × 3600 ≈ 206,265 arcseconds, and because focal lengths are often given in millimeters and pixel sizes in micrometers which yields another factor of 1,000,

3280-427: 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. The word steganography comes from Greek steganographia , which combines

3362-565: The Sigma 35 mm f/1.4 DG HSM lens mounted on a Nikon D800 has the highest measured P-MPix. However, with a value of 23 MP, it still wipes off more than one-third of the D800's 36.3 MP sensor. In August 2019, Xiaomi released the Redmi Note 8 Pro as the world's first smartphone with 64 MP camera. On December 12, 2019 Samsung released Samsung A71 that also has a 64 MP camera. In late 2019, Xiaomi announced

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3444-672: The noise floor of the carrier. All media can be a carrier, but media with a large amount of redundant or compressible information is better suited. From an information theoretical point of view, that means that the channel must have more capacity than the "surface" signal requires. There must be redundancy . For a digital image, it may be noise from the imaging element; for digital audio , it may be noise from recording techniques or amplification equipment. In general, electronics that digitize an analog signal suffer from several noise sources, such as thermal noise , flicker noise , and shot noise . The noise provides enough variation in

3526-494: The original PC . Pixilation , spelled with a second i , is an unrelated filmmaking technique that dates to the beginnings of cinema, in which live actors are posed frame by frame and photographed to create stop-motion animation. An archaic British word meaning "possession by spirits ( pixies )", the term has been used to describe the animation process since the early 1950s; various animators, including Norman McLaren and Grant Munro , are credited with popularizing it. A pixel

3608-529: The " Information Hiding " book published by Springer. All information hiding techniques that may be used to exchange steganograms in telecommunication networks can be classified under the general term of network steganography. This nomenclature was originally introduced by Krzysztof Szczypiorski in 2003. Contrary to typical steganographic methods that use digital media (images, audio and video files) to hide data, network steganography uses communication protocols' control elements and their intrinsic functionality. As

3690-410: The "anchor" to which all other absolute measurements (e.g. the "centimeter") are based on. Worked example, with a 30-inch (76 cm) 2160p TV placed 56 inches (140 cm) away from the viewer: A browser will then choose to use the 1.721× pixel size, or round to a 2× ratio. A megapixel ( MP ) is a million pixels; the term is used not only for the number of pixels in an image but also to express

3772-436: The "total" pixel count. The number of pixels is sometimes quoted as the "resolution" of a photo. This measure of resolution can be calculated by multiplying the width and height of a sensor in pixels. Digital cameras use photosensitive electronics, either charge-coupled device (CCD) or complementary metal–oxide–semiconductor (CMOS) image sensors, consisting of a large number of single sensor elements, each of which records

3854-534: The 1888 German patent of Paul Nipkow . According to various etymologies, the earliest publication of the term picture element itself was in Wireless World magazine in 1927, though it had been used earlier in various U.S. patents filed as early as 1911. Some authors explain pixel as picture cell, as early as 1972. In graphics and in image and video processing, pel is often used instead of pixel . For example, IBM used it in their Technical Reference for

3936-589: The 24 June 1948 issue of Paper Trade Journal by the Technical Director of the United States Government Printing Office had Morris S. Kantrowitz describe in general terms the development of this paper. Three prototype papers ( Sensicoat , Anilith , and Coatalith ) were used to manufacture postcards and stationery provided to German prisoners of war in the US and Canada. If POWs tried to write

4018-634: The Moon and Mars. Billingsley had learned the word from Keith E. McFarland, at the Link Division of General Precision in Palo Alto , who in turn said he did not know where it originated. McFarland said simply it was "in use at the time" ( c.  1963 ). The concept of a "picture element" dates to the earliest days of television, for example as " Bildpunkt " (the German word for pixel , literally 'picture point') in

4100-406: The ability of a soul specially empowered by God to reach, by magical means, from earth to Heaven". Robert Hooke suggested, in the chapter o f Dr. Dee's Book of Spirits , that John Dee used Trithemian steganography to conceal his communication with Queen Elizabeth I . Steganography Steganography ( / ˌ s t ɛ ɡ ə ˈ n ɒ ɡ r ə f i / STEG -ə- NOG -rə-fee )

4182-662: The allocation of the primary colors (green has twice as many elements as red or blue in the Bayer arrangement). DxO Labs invented the Perceptual MegaPixel (P-MPix) to measure the sharpness that a camera produces when paired to a particular lens – as opposed to the MP a manufacturer states for a camera product, which is based only on the camera's sensor. The new P-MPix claims to be a more accurate and relevant value for photographers to consider when weighing up camera sharpness. As of mid-2013,

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4264-529: The basic addressable elements in a viewpoint of hardware, and hence pixel circuits rather than subpixel circuits is used. Most digital camera image sensors use single-color sensor regions, for example using the Bayer filter pattern, and in the camera industry these are known as pixels just like in the display industry, not subpixels . For systems with subpixels, two different approaches can be taken: This latter approach, referred to as subpixel rendering , uses knowledge of pixel geometry to manipulate

4346-448: The best quality and can introduce some random bits. This can also be affected by the file compression done on the image. Secret messages can be introduced into the least significant bits in an image and then hidden. A steganography tool can be used to camouflage the secret message in the least significant bits but it can introduce a random area that is too perfect. This area of perfect randomization stands out and can be detected by comparing

4428-503: The captured digital information that it can be exploited as a noise cover for hidden data. In addition, lossy compression schemes (such as JPEG ) always introduce some error to the decompressed data, and it is possible to exploit that for steganographic use, as well. Although steganography and digital watermarking seem similar, they are not. In steganography, the hidden message should remain intact until it reaches its destination. Steganography can be used for digital watermarking in which

4510-482: The channel file must be transmitted to the recipient with no additional noise from the transmission. Printing introduces much noise in the ciphertext, generally rendering the message unrecoverable. There are techniques that address this limitation, one notable example being ASCII Art Steganography. Although not classic steganography, some types of modern color laser printers integrate the model, serial number, and timestamps on each printout for traceability reasons using

4592-494: The codebook partition by using Graph theory along with Quantization Index Modulation in low bit-rate streaming media. In 2011 and 2012, Yongfeng Huang and Shanyu Tang devised new steganographic algorithms that use codec parameters as cover object to realise real-time covert VoIP steganography. Their findings were published in IEEE Transactions on Information Forensics and Security . In 2024, Cheddad & Cheddad proposed

4674-727: The concealed word VICIPEDIA . Numerous techniques throughout history have been developed to embed a message within another medium. 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 . 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

4756-426: The cover message (in binary data, the number of bits ) relative to the hidden message, the easier it is to hide the hidden message (as an analogy, the larger the "haystack", the easier it is to hide a "needle"). So digital pictures , which contain much data, are sometimes used to hide messages on the Internet and on other digital communication media. It is not clear how common this practice actually is. For example,

4838-457: The current contents of the site. The differences, if the carrier is the same, comprise the payload. In general, using extremely high compression rates makes steganography difficult but not impossible. Compression errors provide a hiding place for data, but high compression reduces the amount of data available to hold the payload, raising the encoding density, which facilitates easier detection (in extreme cases, even by casual observation). There are

4920-521: The depth is normally the sum of the bits allocated to each of the red, green, and blue components. Highcolor , usually meaning 16 bpp, normally has five bits for red and blue each, and six bits for green, as the human eye is more sensitive to errors in green than in the other two primary colors. For applications involving transparency, the 16 bits may be divided into five bits each of red, green, and blue, with one bit left for transparency. A 24-bit depth allows 8 bits per component. On some systems, 32-bit depth

5002-480: The final image. These sensor elements are often called "pixels", even though they only record one channel (only red or green or blue) of the final color image. Thus, two of the three color channels for each sensor must be interpolated and a so-called N-megapixel camera that produces an N-megapixel image provides only one-third of the information that an image of the same size could get from a scanner. Thus, certain color contrasts may look fuzzier than others, depending on

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5084-452: The first camera phone with 108 MP 1/1.33-inch across sensor. The sensor is larger than most of bridge camera with 1/2.3-inch across sensor. One new method to add megapixels has been introduced in a Micro Four Thirds System camera, which only uses a 16 MP sensor but can produce a 64 MP RAW (40 MP JPEG) image by making two exposures, shifting the sensor by a half pixel between them. Using a tripod to take level multi-shots within an instance,

5166-427: The formula is often quoted as s = 206 p / f . The number of distinct colors that can be represented by a pixel depends on the number of bits per pixel (bpp). A 1 bpp image uses 1 bit for each pixel, so each pixel can be either on or off. Each additional bit doubles the number of colors available, so a 2 bpp image can have 4 colors, and a 3 bpp image can have 8 colors: For color depths of 15 or more bits per pixel,

5248-612: 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 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

5330-414: The idea of a mystic-magical foundation of the third volume. Additionally, while Trithemius's steganographic methods can be established to be free of the need for angelic–astrological mediation, an underlying theological motive for their contrivance remains. The preface to Polygraphia equally establishes the everyday practicability of cryptography, and was conceived by Trithemius as a "secular consequent of

5412-544: The image has been tampered with. That is the key difference between steganography and digital watermarking. In 2010, the Federal Bureau of Investigation alleged that the Russian foreign intelligence service uses customized steganography software for embedding encrypted text messages inside image files for certain communications with "illegal agents" (agents without diplomatic cover) stationed abroad. Pixel Each pixel

5494-405: The least significant bits to the next-to-least significant bits on an image that hasn't been compressed. Generally, though, there are many techniques known to be able to hide messages in data using steganographic techniques. None are, by definition, obvious when users employ standard applications, but some can be detected by specialist tools. Others, however, are resistant to detection—or rather it

5576-406: The message that is being hidden is a factor in how difficult it is to detect. The overall size of the cover object also plays a factor as well. If the cover object is small and the message is large, this can distort the statistics and make it easier to detect. A larger cover object with a small message decreases the statistics and gives it a better chance of going unnoticed. Steganalysis that targets

5658-495: The most relevant ones to digital steganographic systems: The payload is the data covertly communicated. The carrier is the signal, stream, or data file that hides the payload, which differs from the channel , which typically means the type of input, such as a JPEG image. The resulting signal, stream, or data file with the encoded payload is sometimes called the package , stego file , or covert message . The proportion of bytes, samples, or other signal elements modified to encode

5740-479: The naked eye; graphics made under these limitations may be called pixel art , especially in reference to video games. Modern computers and displays, however, can easily render orders of magnitude more pixels than was previously possible, necessitating the use of large measurements like the megapixel (one million pixels). The word pixel is a combination of pix (from "pictures", shortened to "pics") and el (for " element "); similar formations with ' el' include

5822-401: The number of image sensor elements of digital cameras or the number of display elements of digital displays . For example, a camera that makes a 2048 × 1536 pixel image (3,145,728 finished image pixels) typically uses a few extra rows and columns of sensor elements and is commonly said to have "3.2 megapixels" or "3.4 megapixels", depending on whether the number reported is the "effective" or

5904-458: The payload is called the encoding density and is typically expressed as a number between 0 and 1. In a set of files, the files that are considered likely to contain a payload are suspects . A suspect identified through some type of statistical analysis can be referred to as a candidate . Detecting physical steganography requires a careful physical examination, including the use of magnification, developer chemicals, and ultraviolet light . It

5986-915: The potential for covert channel signaling in general network communication protocols, even if the traffic is encrypted (in a footnote) in "Encryption-Based Protection for Interactive User/Computer Communication," Proceedings of the Fifth Data Communications Symposium, September 1977. In 1987, Girling first studied covert channels on a local area network (LAN), identified and realised three obvious covert channels (two storage channels and one timing channel), and his research paper entitled “Covert channels in LAN’s” published in IEEE Transactions on Software Engineering , vol. SE-13 of 2, in February 1987. In 1989, Wolf implemented covert channels in LAN protocols, e.g. using

6068-532: 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). , and including data in ignored sections of a file. Since the era of evolving network applications, steganography research has shifted from image steganography to steganography in streaming media such as Voice over Internet Protocol (VoIP). In 2003, Giannoula et al. developed

6150-460: The publication of a decryption key to the first two volumes in 1606, they were discovered to be actually concerned with cryptography and steganography. Until recently, the third volume was widely believed to be solely about magic, but the "magical" formulas have now been shown to be covertexts for yet more material on cryptography. References within the third book to magical works by such figures as Agrippa and John Dee still lend credence to

6232-598: The reserved fields, pad fields, and undefined fields in the TCP/IP protocol. In 1997, Rowland used the IP identification field, the TCP initial sequence number and acknowledge sequence number fields in TCP/IP headers to build covert channels. In 2002, Kamran Ahsan made an excellent summary of research on network steganography. In 2005, Steven J. Murdoch and Stephen Lewis contributed a chapter entitled "Embedding Covert Channels into TCP/IP" in

6314-407: The states of IoT/CPS actuators. Digital steganography output may be in the form of printed documents. A message, the plaintext , may be first encrypted by traditional means, producing a ciphertext . Then, an innocuous cover text is modified in some way so as to contain the ciphertext, resulting in the stegotext . For example, the letter size, spacing, typeface , or other characteristics of

6396-678: The term inter-protocol steganography. Alternatively, multiple network protocols can be used simultaneously to transfer hidden information and so-called control protocols can be embedded into steganographic communications to extend their capabilities, e.g. to allow dynamic overlay routing or the switching of utilized hiding methods and network protocols. Network steganography covers a broad spectrum of techniques, which include, among others: Discussions of steganography generally use terminology analogous to and consistent with conventional radio and communications technology. However, some terms appear specifically in software and are easily confused. These are

6478-453: The three colored subpixels separately, producing an increase in the apparent resolution of color displays. While CRT displays use red-green-blue-masked phosphor areas, dictated by a mesh grid called the shadow mask, it would require a difficult calibration step to be aligned with the displayed pixel raster, and so CRTs do not use subpixel rendering. The concept of subpixels is related to samples . In graphic, web design, and user interfaces,

6560-424: The underlying messages visible only to certain readers. Examples include: 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

6642-508: The words voxel ' volume pixel ' , and texel ' texture pixel ' . The word pix appeared in Variety magazine headlines in 1932, as an abbreviation for the word pictures , in reference to movies. By 1938, "pix" was being used in reference to still pictures by photojournalists. The word "pixel" was first published in 1965 by Frederic C. Billingsley of JPL , to describe the picture elements of scanned images from space probes to

6724-446: 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. 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,

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