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- 2. The History Theword steganography has Greek origins and means ‘concealed writing.’ The original practice can be traced back to around 440 BC when the ancient Greeks hid messages within wax tablets by writing messages on the wood before applying a wax surface (Herodotus 1987). Another early recorded use of steganography occurred in ancient Greece when messengers tattooed messages on their shaved heads and concealed the messages with the hair that grew over them afterwards, a technique also used by German spies in the early 20th century (Newman 1940). With the advent of tiny images, in the Russo-Japanese War (1905) microscopic images were hidden in ears, nostrils, or under fingernails (Stevens 1957); during both World Wars messages were reduced to microdots and stuck on top of printed periods or commas in innocent cover material such as magazines, or inserted into slits of the edges of postcards (Newman 1940; Hoover 1946). In both World Wars invisible inks were also used extensively to write messages under visible text (Kahn 1967). The application of special inks is still used today in the field of currency security to write a hidden message on bank notes or other secure documents.
- 3. Recent Past Sincethe 1980s, with the advent of computer technologies, digital equivalents of these camouflage techniques were invented to hide messages in digital cover media, such as images, video, and audio signals (Fridrich 2009). For example, in 2010, the United States Department of Justice documented that more than 100 text files were retrieved from images posted on publicly accessible Web sites. According to the Steganography Analysis and Research Centre, there have been over 1,100 digital steganography applications identified. Most of the digital steganography systems exploit the redundancy of the cover media and rely on the limitations of the human auditory or visual systems. For example, a standard image steganography system uses the least-significant- bit substitution technique. Because the difference between 11111111 and 11111110 in the value for red/green/blue intensity is likely to be undetectable by the human eye, the least-significant-bit can be used to hide information other than color, without being perceptable by a human observer.
- 4. Information Hiding Steganographyis a branch of security concerned with hiding information in some cover medium Use of images for hiding information has been extensively studied Make changes to an image so that the changes are imperceptible to an observer The resulting image encodes the message. A related area is watermarking, which is concerned with hiding information for the purposes of identification (e.g. copyright)
- 5. Terminology a legitimatecommunication among the two parties is called a cover object, a message with embedded hidden information is called a stego object, where object stands for “text,” “image,” “audio,” or whatever media is being used. The algorithms that Sender uses for creating the stego object and Receiver uses for decoding the message are collectively called a stegosystem.
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- 7. Information Hiding mfbuyiwubfstidttmnttgilaumwuniptcosnatpttafsotncaiaswttitintplpft btxlfanhtitqompca π =3.141592653589793 . . . buubdlupnpsspx attack tomorrow My friend Bob, until yesterday I was using binoculars for stargazing. Today, I decided to try my new telescope. The galaxies in Leo and Ursa Major were unbelievable! Next, I plan to check out some nebulas and then prepare to take a few snapshots of the new comet. Although I am satisfied with the telescope, I think I need to purchase light pollution filters to block the xenon lights from a nearby highway to improve the quality of my pictures. Cheers, Alice.
- 8. Live Example Exercise:Lets use an image and hide our message “Are you Hiding Something” into the image. Can we do it using simple tools already available in our systems? Let us C echo "Your Message">>"image.jpg“ copy /b text.txt + image.jpg newimage.jpg md
- 9. Live Example: HidingText into Image using Command Prompt
- 10. The Trade-off Astegosystem has to fulfil two fundamental requirements. The first and foremost requirement is security. This means that the stegomedia in which the secret message is hidden must be unsuspicious according to a human or a computer. The second requirement is payload capacity, The payload is the size of the secret message that the sender wishes to conceal and transport relative to the size of the cover media. Because steganography aims at covert information transmission, it requires sufficient embedding capacity. An ideal stegosystem would have a high level of security and large payload capacity. However, there is a fundamental trade-off between security and payload because any attempt to embed additional information in the cover media is likely to increase the chance of introducing anomalies into the media, thus degrading the security level.
- 11. Linguistic Steganography Akey question for any stegosystem is the choice of cover medium. Given the ubiquitous nature of natural language and the omnipresence of text, text is an obvious medium to consider. The advantage of this method is that the secret message appears as some normal communication that may not arouse suspicion. Howeverit is difficult creating meaningful and natural text from scratch and of hiding messages in it using just NLP techniques. Therefore, most of the existing linguistic stegosystems take already-existing text as the cover text, and linguistic properties of the text are used to modify it and hide information
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- 13. Please Note: Assumean existing cover text which will be modified (rather than generated from scratch) the receiver does not need a copy of the cover text (just the code dictionary for lexical substitution) this is not a cryptography problem Possible Linguistic Transformations Lexical (e.g. synonym substitution) Syntactic (e.g. passive/active transformation) Semantic/pragmatic Linguistic Steganography Framework
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- 15. Watermarking and Steganography A related area to steganography is digital watermarking. Changes are made to a cover medium in order to verify its authenticity or to show the identity of its owners for example, for copyright purposes, traitor tracing etc. Both steganography and watermarking use steganographic techniques to embed information in cover media. However, steganography aims for the imperceptibility of a secret message to an observer, whereas watermarking tries to mark cover media with information that is robust against modifications or for the purpose of tamperproofing. For steganography a user can have the freedom to choose the cover medium to carry messages, whereas for watermarking the cover medium is already decided.