In computing , a computer file is a resource for recording data on a computer storage device , primarily identified by its filename . Just as words can be written on paper, so too can data be written to a computer file. Files can be shared with and transferred between computers and mobile devices via removable media , networks , or the Internet .
123-397: Steganography ( / ˌ s t ɛ ɡ ə ˈ n ɒ ɡ r ə f i / STEG -ə- NOG -rə-fee ) is the practice of representing information within another message or physical object, in such a manner that the presence of the concealed information would not be evident to an unsuspecting person's examination. In computing/electronic contexts, a computer file , message, image, or video
246-707: A file of punched cards ." In February 1950, in a Radio Corporation of America (RCA) advertisement in Popular Science magazine describing a new "memory" vacuum tube it had developed, RCA stated: "the results of countless computations can be kept 'on file' and taken out again. Such a 'file' now exists in a 'memory' tube developed at RCA Laboratories. Electronically it retains figures fed into calculating machines, holds them in storage while it memorizes new ones – speeds intelligent solutions through mazes of mathematics." In 1952, "file" denoted, among other things, information stored on punched cards . In early use,
369-671: A blacklight or other UV light source. Security marker pens can be obtained commercially and are widely used as a crime countermeasure. Some commercially available invisible inks glow very brightly, in a variety of colors, under ultraviolet light. This makes them suitable for use in readmission such as hand stamping. There are some invisible ink types that can only be invisible when applied to certain types of surfaces, but are still visible on others. Some vendors now offer invisible ink for use in computer inkjet printers . Such inks are usually visible under ultraviolet light. Typical uses include printing information on business forms for use by
492-462: A hard disk . Hard disks have been the ubiquitous form of non-volatile storage since the early 1960s. Where files contain only temporary information, they may be stored in RAM . Computer files can be also stored on other media in some cases, such as magnetic tapes , compact discs , Digital Versatile Discs , Zip drives , USB flash drives , etc. The use of solid state drives is also beginning to rival
615-428: A link to the file. There can be many links to a file, but when they are all removed, the kernel considers that file's memory space free to be reallocated. This free space is commonly considered a security risk (due to the existence of file recovery software ). Any secure-deletion program uses kernel-space (system) functions to wipe the file's data. File moves within a file system complete almost immediately because
738-413: 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
861-523: A " decoder pen " which is used to show the invisible parts of texts or pictures, thus revealing answers to questions printed in regular ink or completing missing parts of pictures. Security marker pens or UV markers with fluorescent ink that glows when illuminated with a UV light is often used to invisibly mark valuable household items in case of burglary . There are specialty security maker pens formulated for writing on non-porous surfaces such as glass , plastic , metal , etc. The mark can be read by using
984-428: 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
1107-454: A FAT extension allowing long file names). File manager programs are utility programs that allow users to manipulate files directly. They allow you to move, create, delete and rename files and folders, although they do not actually allow you to read the contents of a file or store information in it. Every computer system provides at least one file-manager program for its native file system. For example, File Explorer (formerly Windows Explorer)
1230-443: A back-up method of communication when other, more secure communication techniques were unavailable. The agency was known to supply special inks to its field agents, rather than have them depend upon improvisation from obtainable everyday chemicals. When agents were forced to improvise, they were advised to dilute their invisible ink as much as possible to reduce chances of detection. Any invisible ink can be made visible by someone who
1353-519: 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, 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
SECTION 10
#17327874389671476-402: A careful observer who simply makes use of strong light, a magnifying glass and their nose. Also, key words in the visible letter, such as "heat" or any other odd code name, in an out of place context may alert a censor to the presence of invisible ink. Invisible ink is not effective with glossy or very smooth paper types, since the sizing of these papers prevents ink from being absorbed deep into
1599-446: A chemical compound extracted from pills for constipation , were used as invisible ink. It is colorless but turns pink when exposed to alkali such as ammonia and bicarbonate soda . Invisible ink can be applied to a writing surface with a specialty purpose stylus , stamp , fountain pen , toothpick , calligraphy pen , Cotton swab , or even a finger dipped in the liquid. Once dry, the written surface looks as if it were blank, with
1722-422: A confirmation code only for the voted selection. What an "ideal" invisible ink is depends on its intended use. For example, property marking should ideally be done with ink easily read under ultraviolet light, whereas in espionage such an ink would be considered too easily detectable since a large number of letters may be screened relatively quickly using UV light. Invisible inks are inherently "insecure" against
1845-415: 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,
1968-410: 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
2091-437: A determined and well-equipped inspector, which must be balanced against the logistical difficulty in carrying out mass-screening of posted mail. It is easier to perform large-scale undetected screening of millions of electronic communications, than to mass-screen even a small fraction of conventional mail. Apart from in dictatorships where large numbers of personnel are employed to spy on fellow nationals, screening of posted mail
2214-427: A device, no space will have been freed up on the source device or partition. The user would need to merge the remaining files from the source, including the incompletely written (truncated) last file. With the individual deletion method, the file moving software also does not need to cumulatively keep track of all files finished transferring for the case that a user manually aborts the file transfer. A file manager using
2337-524: A directory and a file. In environments in which a file is named, a file's name and the path to the file's directory must uniquely identify it among all other files in the computer system—no two files can have the same name and path. Where a file is anonymous, named references to it will exist within a namespace. In most cases, any name within the namespace will refer to exactly zero or one file. However, any file may be represented within any namespace by zero, one or more names. Any string of characters may be
2460-847: A dot (period) at the end of a file name, followed by a few letters to identify the type of file. An extension of .txt identifies a text file; a .doc extension identifies any type of document or documentation, commonly in the Microsoft Word file format ; and so on . Even when extensions are used in a computer system, the degree to which the computer system recognizes and heeds them can vary; in some systems, they are required, while in other systems, they are completely ignored if they are presented. Many modern computer systems provide methods for protecting files against accidental and deliberate damage. Computers that allow for multiple users implement file permissions to control who may or may not modify, delete, or create files and folders. For example,
2583-480: 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
SECTION 20
#17327874389672706-514: A given user may be granted only permission to read a file or folder, but not to modify or delete it; or a user may be given permission to read and modify files or folders, but not to execute them. Permissions may also be used to allow only certain users to see the contents of a file or folder. Permissions protect against unauthorized tampering or destruction of information in files, and keep private information confidential from unauthorized users. Another protection mechanism implemented in many computers
2829-531: 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
2952-446: A later point through overwriting. There are many ways by which a file can become corrupted. Most commonly, the issue happens in the process of writing the file to a disk . For example, if an image-editing program unexpectedly crashes while saving an image, that file may be corrupted because the program could not save its entirety. The program itself might warn the user that there was an error, allowing for another attempt at saving
3075-420: A low level, on a file. Only the kernel deals with files, and it handles all user-space interaction with files in a manner that is transparent to the user-space programs. The operating system provides a level of abstraction , which means that interaction with a file from user-space is simply through its filename (instead of its inode ). For example, rm filename will not delete the file itself, but only
3198-803: 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
3321-491: 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
3444-412: 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
3567-618: A message will prevent writing from being developed by this method, but overdoing dampening will result in telltale paper cockling. Former MI6 agent Richard Tomlinson stated that Pentel Rolling Writer rollerball pens were extensively used by MI-6 agents to produce secret writing in the form of invisible messages while on missions. In 2002, a gang was indicted for spreading a riot between federal penitentiaries using coded telephone messages, and messages in invisible ink. In 1995, President Clinton issued an executive order requesting that all agencies declassify information 25 years or older by
3690-406: A name of its own, but also a path, which identifies the folder or folders in which a file or folder resides. In the path, some sort of special character—such as a slash—is used to separate the file and folder names. For example, in the illustration shown in this article, the path /Payroll/Salaries/Managers uniquely identifies a file called Managers in a folder called Salaries , which in turn
3813-618: A near opposite way by absorbing ultraviolet light but without fluorescing. When these are used on fluorescent paper, the inked areas fluoresce less than the surrounding paper area when under an ultraviolet lamp. This is especially a property of inks with a yellow tint. Some UV-visible inks may be detected on a photocopy, due to the relatively strong ultraviolet component in light from the photocopier scanning head. Examples of inks revealed by ultraviolet light are: This includes virtually all invisible inks, but pure distilled water can also be used in this way. Application of any fluid will alter
Steganography - Misplaced Pages Continue
3936-599: 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
4059-418: A number of bytes , that indicates how much storage is occupied by the file. In most modern operating systems the size can be any non-negative whole number of bytes up to a system limit. Many older operating systems kept track only of the number of blocks or tracks occupied by a file on a physical storage device. In such systems, software employed other methods to track the exact byte count (e.g., CP/M used
4182-406: 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
4305-443: A payroll file might contain information concerning all the employees in a company and their payroll details; each record in the payroll file concerns just one employee, and all the records have the common trait of being related to payroll—this is very similar to placing all payroll information into a specific filing cabinet in an office that does not have a computer. A text file may contain lines of text, corresponding to printed lines on
4428-429: A piece of paper. Alternatively, a file may contain an arbitrary binary image (a blob ) or it may contain an executable . The way information is grouped into a file is entirely up to how it is designed. This has led to a plethora of more or less standardized file structures for all imaginable purposes, from the simplest to the most complex. Most computer files are used by computer programs which create, modify or delete
4551-475: 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
4674-465: 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
4797-438: A similar texture and reflectivity as the surrounding surface. The ink can be later made visible by different methods according to the type of invisible ink used. The ink may be revealed by heat or by application of an appropriate chemical, or it may be made visible by viewing under ultraviolet light . Inks which are developed by a chemical reaction may depend on an acid-base reaction (like litmus paper ), reactions similar to
4920-433: A special control character, Ctrl-Z , to signal the end of text files). The general definition of a file does not require that its size have any real meaning, however, unless the data within the file happens to correspond to data within a pool of persistent storage. A special case is a zero byte file ; these files can be newly created files that have not yet had any data written to them, or may serve as some kind of flag in
5043-584: A tiny hole above or below letters in a document to spell out a secret message. This did not include an invisible ink but the Germans improved on the method during World War I and World War II . They used invisible ink and microdots instead of pinpricks. Philo of Byzantium may be the first writer known to describe an invisible ink using a reagent around 217–218 BC, with oak galls and vitriol . These ingredients were used to make oak gall ink . People soon discovered that they could write invisibly with one of
Steganography - Misplaced Pages Continue
5166-438: A tree-like structure in which one "master folder" (or "root folder" — the name varies from one operating system to another) can contain any number of levels of other folders and files. Folders can be named just as files can (except for the root folder, which often does not have a name). The use of folders makes it easier to organize files in a logical way. When a computer allows the use of folders, each file and folder has not only
5289-585: 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
5412-425: 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
5535-419: A well-formed name for a file or a link depending upon the context of application. Whether or not a name is well-formed depends on the type of computer system being used. Early computers permitted only a few letters or digits in the name of a file, but modern computers allow long names (some up to 255 characters) containing almost any combination of Unicode letters or Unicode digits, making it easier to understand
5658-444: A written message, a document, a spreadsheet , an image , a video , a program , or any wide variety of other kinds of data. Certain files can store multiple data types at once. By using computer programs, a person can open, read, change, save, and close a computer file. Computer files may be reopened, modified, and copied an arbitrary number of times. Files are typically organized in a file system , which tracks file locations on
5781-436: Is a read-only flag. When this flag is turned on for a file (which can be accomplished by a computer program or by a human user), the file can be examined, but it cannot be modified. This flag is useful for critical information that must not be modified or erased, such as special files that are used only by internal parts of the computer system. Some systems also include a hidden flag to make certain files invisible; this flag
5904-467: 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
6027-413: 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
6150-479: Is an area of memory which is manipulated to establish a filename etc. and then passed to the operating system as a parameter; it was used by older IBM operating systems and early PC operating systems including CP/M and early versions of MS-DOS . A file handle is generally either an opaque data type or an integer; it was introduced in around 1961 by the ALGOL-based Burroughs MCP running on
6273-486: 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
SECTION 50
#17327874389676396-472: Is commonly used in Microsoft Windows operating systems, and Nautilus is common under several distributions of Linux. Invisible ink Invisible ink , also known as security ink or sympathetic ink , is a substance used for writing, which is invisible either on application or soon thereafter, and can later be made visible by some means, such as heat or ultraviolet light. Invisible ink
6519-413: Is concealed within another file, message, image, or video. The word steganography comes from Greek steganographia , which combines the words steganós ( στεγανός ), meaning "covered or concealed", and -graphia ( γραφή ) meaning "writing". The first recorded use of the term was in 1499 by Johannes Trithemius in his Steganographia , a treatise on cryptography and steganography, disguised as
6642-420: Is contained in a folder called Payroll . The folder and file names are separated by slashes in this example; the topmost or root folder has no name, and so the path begins with a slash (if the root folder had a name, it would precede this first slash). Many computer systems use extensions in file names to help identify what they contain, also known as the file type. On Windows computers, extensions consist of
6765-464: Is corrupted. There are services that provide on demand file corruption, which essentially fill a given file with random data so that it cannot be opened or read, yet still seems legitimate. One of the most effective countermeasures for unintentional file corruption is backing up important files. In the event of an important file becoming corrupted, the user can simply replace it with the backed up version. When computer files contain information that
6888-613: Is extremely important, a back-up process is used to protect against disasters that might destroy the files. Backing up files simply means making copies of the files in a separate location so that they can be restored if something happens to the computer, or if they are deleted accidentally. There are many ways to back up files. Most computer systems provide utility programs to assist in the back-up process, which can become very time-consuming if there are many files to safeguard. Files are often copied to removable media such as writable CDs or cartridge tapes. Copying files to another hard disk in
7011-437: 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
7134-501: Is one form of steganography . One of the earliest writers to mention an invisible ink is Aeneas Tacticus , in the 4th century BC. He mentions it in discussing how to survive under siege but does not indicate the type of ink to be used. This was part of his list of the 20 different methods of secret communications in a book called On the Defense of Fortifications . One of the techniques that involved steganography involved puncturing
7257-531: Is only feasible in particular situations, such as letters to and from a particular suspect or facility. The British SOE training manual used in the Second World War identified the following properties of an "ideal" invisible ink: From practical experience "6" and "9" were usually incompatible. SOE agents were trained not to risk their lives through reliance on insecure inks, most of which were from World War I. In general, SOE used invisible inks as
7380-480: 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
7503-472: Is sufficiently determined, but the limitation is generally time available and the fact that one cannot apply hours of effort to every single piece of paper. Thus successful use of invisible ink depends on not arousing suspicion that invisible ink may be present. Telltale signs of invisible ink, such as pen scratches from a sharp pen, roughness, or changed reflectivity of the paper (either more dull or more shiny, usually from using undiluted ink), can be obvious to
SECTION 60
#17327874389677626-404: Is that the intended secret message does not attract attention to itself as an object of scrutiny. Plainly visible encrypted messages, no matter how unbreakable they are, arouse interest and may in themselves be incriminating in countries in which encryption is illegal. Whereas cryptography is the practice of protecting the contents of a message alone, steganography is concerned with concealing both
7749-435: Is used by the computer system to hide essential system files that users should not alter. Any file that has any useful purpose must have some physical manifestation. That is, a file (an abstract concept) in a real computer system must have a real physical analogue if it is to exist at all. In physical terms, most computer files are stored on some type of data storage device. For example, most operating systems store files on
7872-627: The mv command for instance, the former method is used when selecting files individually, possibly with the use of wildcards (example: mv -n sourcePath/* targetPath , while the latter method is used when selecting entire directories (example: mv -n sourcePath targetPath ). Microsoft Windows Explorer uses the former method for mass storage file moves, but the latter method using Media Transfer Protocol , as described in Media Transfer Protocol § File move behavior . The former method (individual deletion from source) has
7995-468: The Burroughs B5000 but is now ubiquitous. When a file is said to be corrupted, it is because its contents have been saved to the computer in such a way that they cannot be properly read, either by a human or by software. Depending on the extent of the damage, the original file can sometimes be recovered , or at least partially understood. A file may be created corrupt, or it may be corrupted at
8118-641: The Horniman Museum in London. The illustrations, drawn on the walls and floor of the Music Gallery Performance Space, were only visible under UV light. Inks that are visible for a period of time without the intention of being made visible again are called disappearing inks. Disappearing inks typically rely on the chemical reaction between thymolphthalein and a basic substance such as sodium hydroxide . Thymolphthalein, which
8241-619: The NTFS file system that is the normal file system for recent versions of Windows. Each system has its own advantages and disadvantages. Standard FAT allows only eight-character file names (plus a three-character extension) with no spaces, for example, whereas NTFS allows much longer names that can contain spaces. You can call a file " Payroll records " in NTFS, but in FAT you would be restricted to something like payroll.dat (unless you were using VFAT ,
8364-622: The National Archives until their declassification in 2011. At this time, the CIA no longer considered the documents sensitive due to recent advancements in technology. Invisible ink is not commonly used in art. Some artists, however, have incorporated invisible ink into their work, either alone or in conjunction with more conventional media. Jean-Michel Basquiat is known to have worked with invisible ink. In 2012, Sotheby's London discovered Basquiat's signature painted in invisible ink on
8487-471: The blueprint process, or any of hundreds of others. Developer fluids may be applied using a spray bottle, but some developers are in the form of vapor, e.g. ammonia fumes used to develop phenolphthalein ink. There are also toy invisible ink pens which have two tips—one tip for invisible ink writing, and another tip for developing the ink. Invisible ink is sometimes used to print parts of pictures or text in books for children to play with, always including
8610-672: 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
8733-527: 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
8856-554: The 1982 work, Orange Sports Figure . In 2018, analysis by an art conservator revealed invisible ink markings on an untitled Basquiat painting from 1981. In 2012, the Hayward Gallery exhibition, Invisible: Art about the Unseen, 1957-2012 , included the 1989 work, Magic Ink , by Gianni Motti. It consisted of two drawings created with undeveloped invisible ink. In 2015, Aowen Jin exhibited artwork drawn in invisible ink at
8979-616: 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
9102-410: The archive file are to lower the number of files for easier transfer, to reduce storage usage, or just to organize outdated files. The archive file must often be unpacked before next using. The most basic operations that programs can perform on a file are: Files on a computer can be created, moved, modified, grown, shrunk ( truncated ), and deleted. In most cases, computer programs that are executed on
9225-407: The benefit that space is released from the source device or partition imminently after the transfer has begun, meaning after the first file is finished. With the latter method, space is only freed after the transfer of the entire selection has finished. If an incomplete file transfer with the latter method is aborted unexpectedly, perhaps due to an unexpected power-off, system halt or disconnection of
9348-448: 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
9471-503: 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
9594-481: 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
9717-498: 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
9840-559: The computer handle these operations, but the user of a computer can also manipulate files if necessary. For instance, Microsoft Word files are normally created and modified by the Microsoft Word program in response to user commands, but the user can also move, rename , or delete these files directly by using a file manager program such as Windows Explorer (on Windows computers) or by command lines (CLI). In Unix-like systems, user space programs do not operate directly, at
9963-727: 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
10086-426: 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,
10209-457: 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
10332-410: The data content does not need to be rewritten. Only the paths need to be changed. There are two distinct implementations of file moves. When moving files between devices or partitions, some file managing software deletes each selected file from the source directory individually after being transferred, while other software deletes all files at once only after every file has been transferred. With
10455-706: The disk and enables user access. The word "file" derives from the Latin filum ("a thread, string"). "File" was used in the context of computer storage as early as January 1940. In Punched Card Methods in Scientific Computation , W. J. Eckert stated, "The first extensive use of the early Hollerith Tabulator in astronomy was made by Comrie . He used it for building a table from successive differences, and for adding large numbers of harmonic terms". "Tables of functions are constructed from their differences with great efficiency, either as printed tables or as
10578-440: The document file is arranged in a format that the word-processing program understands, the user is able to choose the name and location of the file and provide the bulk of the information (such as words and text) that will be stored in the file. Many applications pack all their data files into a single file called an archive file , using internal markers to discern the different types of information contained within. The benefits of
10701-403: The existence of directory hierarchies, i.e., directories containing sub-directories. A name that refers to a file within a directory must be typically unique. In other words, there must be no identical names within a directory. However, in some operating systems, a name may include a specification of type that means a directory can contain an identical name for more than one type of object such as
10824-413: 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 a document file, image file, program, or protocol. Media files are ideal for steganographic transmission because of their large size. For example,
10947-414: The file and the son is the current copy. The way a computer organizes, names, stores and manipulates files is globally referred to as its file system . Most computers have at least one file system. Some computers allow the use of several different file systems. For instance, on newer MS Windows computers, the older FAT-type file systems of MS-DOS and old versions of Windows are supported, in addition to
11070-414: The file system) file-specific data outside of the file format, but linked to the file, for example extended attributes or forks . On other file systems this can be done via sidecar files or software-specific databases. All those methods, however, are more susceptible to loss of metadata than container and archive file formats. At any instant in time, a file has a specific size, normally expressed as
11193-526: The file system, or are accidents (the results of aborted disk operations). For example, the file to which the link /bin/ls points in a typical Unix-like system probably has a defined size that seldom changes. Compare this with /dev/null which is also a file, but as a character special file , its size is not meaningful. Information in a computer file can consist of smaller packets of information (often called " records " or "lines") that are individually different but share some common traits. For example,
11316-423: The file. Some other examples of reasons for which files become corrupted include: Although file corruption usually happens accidentally, it may also be done on purpose as a mean of procrastination , as to fool someone else into thinking an assignment was ready at an earlier date, potentially gaining time to finish said assignment or making experiments, with the purpose of documenting the consequences when such file
11439-402: The files for their own use on an as-needed basis. The programmers who create the programs decide what files are needed, how they are to be used and (often) their names. In some cases, computer programs manipulate files that are made visible to the computer user. For example, in a word-processing program , the user manipulates document files that the user personally names. Although the content of
11562-758: The first book on secret writing and invisible inks, Magia Naturalis (1558, 1589). Since then, a wide variety of invisible inks have been used for all sorts of secretive purposes. A formula similar to oak gall ink was created by James Jay and used by George Washington and the Culper Spy Ring during the American Revolution and lemon juice was used by the 'Lemon Juice Spies' (Carl Muller and four other Germans, who all died for their efforts either by suicide or execution, along with John Hahn, an English baker) during World War I. In World War II, neutral or acidic solutions of phenolphthalein ,
11685-403: The form processor, without cluttering up the visible contents of the form. For example, some United States Postal Service mail sorting stations use UV-visible ink to print bar codes on mailed envelopes giving routing information for use by mail handling equipment further down the line before delivery. An E2E voting system called Scantegrity II uses invisible ink to enable the voter to obtain
11808-439: The hard disk drive. In Unix-like operating systems, many files have no associated physical storage device. Examples are /dev/null and most files under directories /dev , /proc and /sys . These are virtual files: they exist as objects within the operating system kernel. As seen by a running user program, files are usually represented either by a file control block or by a file handle . A file control block (FCB)
11931-658: 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. Computer file Different types of computer files are designed for different purposes. A file may be designed to store
12054-600: The ingredients and then cause the writing to appear by adding the other. Pliny the Elder and the Roman poet Ovid gave advice on the use of plant juices and milk to write secret messages. Lemons were also used as organic inks by Arabs around 600 AD, and during the 16th century in Europe. Giovanni Battista della Porta is credited with the first recipe for a sympathetic ink, derived from alum and vinegar , as well as
12177-407: The inks are listed here according to their method of development. It must be understood however that some inks – particularly those of organic origin or those consisting of a mixture of several chemicals – may be made visible by several methods. For example, invisible writing with soap water may be made visible either by heat, reaction with phenolphthalein, viewing under ultraviolet light, or by placing
12300-510: The invisible ink. Thus, if a censor uses this method to intercept messages, the letter may then be sent to the intended recipient, who will be unaware that the secret message has already been intercepted by a third party. A "screening station" theoretically could involve visual and olfactory inspection, an examination under ultraviolet light and then the heating of all objects in an oven before finally trying exposure to iodine fumes to produce optimal security in optimal time. For practical reasons,
12423-418: The latter (afterwards deletion) method will have to only delete the files from the source directory that have already finished transferring. In modern computer systems, files are typically accessed using names ( filenames ). In some operating systems, the name is associated with the file itself. In others, the file is anonymous, and is pointed to by links that have names. In the latter case, a user can identify
12546-404: 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
12669-406: 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
12792-495: 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
12915-413: The name of the link with the file itself, but this is a false analogue, especially where there exists more than one link to the same file. Files (or links to files) can be located in directories. However, more generally, a directory can contain either a list of files or a list of links to files. Within this definition, it is of paramount importance that the term "file" includes directories. This permits
13038-417: The page inside an iodine fume cupboard. Some of these are organic substances that oxidize when heated, which usually turns them brown. For this type of "heat fixed" ink, any acidic fluid will work. The most secure way to use any of the following substances for invisible ink is by dilution, usually with water, close to the point when they become difficult to develop. The writing is rendered visible by heating
13161-430: The paper and it is easily visible, especially if the paper is examined under glancing light. There are, however, commercially available inks for non-porous surfaces that are only visible under ultraviolet light and are otherwise virtually invisible on such surfaces. Using either ultraviolet light or an iodine fume cupboard, messages can be quickly screened for invisible ink and also read without first permanently developing
13284-412: The paper surface fibers or sizing. Fumes created from heating iodine crystals will develop the writing, which will appear brown because the iodine sticks preferentially to the altered areas of the paper. Exposing the paper to strong sunlight will return the writing to its invisible state, as will using a bleach solution. Slightly dampening paper with a sponge or by steam and then drying it before writing
13407-428: The paper, either on a radiator , by ironing it, using a hair dryer, or by placing it in an oven . A 100-watt light bulb is less likely to damage the paper. In most cases, these substance changes color when mixed with an acid or base . Some inks glow faintly ( fluoresce ) when under an ultraviolet lamp. This is a property of many substances, particularly organic substances and body fluids. Other inks work in
13530-458: 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
13653-936: 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
13776-529: 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
13899-518: The purpose of a file at a glance. Some computer systems allow file names to contain spaces; others do not. Case-sensitivity of file names is determined by the file system . Unix file systems are usually case sensitive and allow user-level applications to create files whose names differ only in the case of characters. Microsoft Windows supports multiple file systems, each with different policies regarding case-sensitivity. The common FAT file system can have multiple files whose names differ only in case if
14022-605: 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
14145-513: The rules for how the bytes must be organized and interpreted meaningfully. For example, the bytes of a plain text file ( .txt in Windows) are associated with either ASCII or UTF-8 characters, while the bytes of image, video, and audio files are interpreted otherwise. Most file types also allocate a few bytes for metadata , which allows a file to carry some basic information about itself. Some file systems can store arbitrary (not interpreted by
14268-402: The same computer protects against failure of one disk, but if it is necessary to protect against failure or destruction of the entire computer, then copies of the files must be made on other media that can be taken away from the computer and stored in a safe, distant location. The grandfather-father-son backup method automatically makes three back-ups; the grandfather file is the oldest copy of
14391-405: 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
14514-675: 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
14637-611: The underlying hardware, rather than the contents stored on it, was denominated a "file". For example, the IBM 350 disk drives were denominated "disk files". The introduction, c. 1961 , by the Burroughs MCP and the MIT Compatible Time-Sharing System of the concept of a " file system " that managed several virtual "files" on one storage device is the origin of the contemporary denotation of
14760-422: 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
14883-580: The user uses a disk editor to edit the file names in the directory entries . User applications, however, will usually not allow the user to create multiple files with the same name but differing in case. Most computers organize files into hierarchies using folders, directories, or catalogs. The concept is the same irrespective of the terminology used. Each folder can contain an arbitrary number of files, and it can also contain other folders. These other folders are referred to as subfolders. Subfolders can contain still more files and folders and so on, thus building
15006-402: The word. Although the contemporary " register file " demonstrates the early concept of files, its use has greatly decreased. On most modern operating systems , files are organized into one-dimensional arrays of bytes . The format of a file is defined by its content since a file is solely a container for data. On some platforms the format is indicated by its filename extension , specifying
15129-506: The year 2000. Six World War I documents referencing the recipes for invisible ink were due to be declassified under this order, including: In 1999, however, the Central Intelligence Agency (CIA) successfully exempted these documents, arguing that the recipes provided the basis for more advanced formulas still in use at the time. This exemption made the recipes for invisible ink the oldest classified documents held by
#966033