The stenography is a set of rules that allow us to hide messages within messages, called carrier. The reason for the Stenography comes with the Prisoner issue, in which two prisoners, Alice A and Bob B are incarcerated in to separated cells, and they want to plan a prison brake. Their only way to communicate is sending messages via the prison guard, Oscar O , who can read all messages, modify them or not to send them if they are suspicious. So, sending an encrypted message is not an option because therefore O, does not understand the message, he can figure out than A and B are up to something. The stenography solves this issue, Since O reads a navy message, but A and B know how to extract the secret message from the carrier. The downside of this method is that if a third party has acces to the message, could suspect that an information exchange is happening, and even if he cannot understand it, take measures against the information exchange.
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The first recorded use of the term was in 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, the hidden message may be in invisible ink between the visible lines of a private letter. Some implementations of steganography that lack a shared secret are forms of security through obscurity , and key-dependent steganographic schemes 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 is illegal. Whereas cryptography is the practice of protecting the contents of a message alone, steganography is concerned both with concealing 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, 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 BC when Herodotus mentions two examples in his Histories. Wax tablets were in common use then as reusable writing surfaces, sometimes used for shorthand. Steganography has been widely used for centuries. Here are some examples: . Modern steganography entered the world in with the advent of personal computers being applied to classical steganography problems.
An image or a text can be converted into a soundfile, which is then analysed with a spectrogram to reveal the image. Various artists have used this method to conceal hidden pictures in their songs, such as Aphex Twin in Windowlicker or Nine Inch Nails in their album Year Zero. 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 the underlying messages visible only to certain readers. 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 , Giannoula et al. In , Dittmann et al. In , Yongfeng Huang and Shanyu Tang presented a novel approach to information hiding in low bit-rate VoIP speech stream, and theirs published work on steganography in  is the first ever effort to improve the codebook partition by using Graph theory along with Quantization Index Modulation in low bit-rate streaming media.
In and , Yongfeng Huang and Shanyu Tang devised new steganographic algorithms that use codec parameters as cover object to realise real-time covert VoIP steganography. However, specific techniques hide data in CPS components. 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 covertext 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 a covertext 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, 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. For instance, steganography using sudoku puzzles has as many keys as there are possible solutions of a sudoku puzzle, which is 6. SE of 2, in February In , Wolf implemented covert channels in LAN protocols, e. In , Kamran Ahsan made an excellent summary of research on network steganography.
In , Steven J. 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 As 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. Moreover, it is feasible to utilize the relation between two or more different network protocols to enable secret communication.
These applications fall under the term inter-protocol steganography. 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 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 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 careful physical examination, including the use of magnification, developer chemicals and ultraviolet light. It 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. 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 a hidden message, the special paper rendered it visible. The US granted at least two patents related to the technology, one to Kantrowitz, U.
Patent 2,, , patented 20 July A similar strategy issues prisoners with writing paper ruled with 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 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 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.
The size of 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 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 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 the least significant bits to the next-to-least significant bits on 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 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  to describe any malicious operation involving steganography as a vehicle to conceal an attack. Detection of steganography 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 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".
The first recorded use of the term was in 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, the hidden message may be in invisible ink between the visible lines of a private letter. Some implementations of steganography that lack a shared secret are forms of security through obscurity , and key-dependent steganographic schemes 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 is illegal. Whereas cryptography is the practice of protecting the contents of a message alone, steganography is concerned both with concealing the fact that a secret message is being sent and its contents.