Examining The Importance Of Steganography Information Technology Essay

Steganography comes from the Greek and literally means,”Covered writing”. It is one of various data hiding techniques, which aims at transmitting a message on a channel where some other kind of information is already being transmitted. This distinguishes steganography from covert channel techniques, which instead of trying to transmit data between two entities that were unconnected before. Steganography is defined by Markus Kahn as follows, “Steganography is the art and science of writing hidden messages in such a way that no one, apart from the sender and intended recipient, suspects the existence of the message, a form of security through obscurity”[1]. The goal of Steganography is to hide messages inside other harmless messages in a way that does not allow any enemy to even detect that there is a second message present”.

The only missing information for the “enemy” is the short easily exchangeable random number sequence, the secret key, without the secret key, the “enemy” should not have the slightest chance of even becoming suspicious that on an observed communication channel, hidden communication might take place.

Steganography is closely related to the problem of “hidden channels” n secure operating system design, a term which refers to all communication paths that cannot easily be restricted by access control mechanisms. In an ideal world we would all be able to sent openly encrypted mail or files to each other with no fear of reprisals. However there are often cases when this is possible, either because the working company does not allow encrypted email or the local government does not approve of encrypt communication (a reality in some parts of the world). This is where steganography can come into play.

Steganography has developed a lot in recent years, because digital techniques allow new ways of hiding informations inside other informations, and this can be valuable in a lot of situations. The first to employ hidden communications techniques -with radio transmissions- were the armies, because of the strategic importance of secure communication and the need to conceal the source as much as possible.

Nowadays, new constraints in using strong encryption for messages are added by international laws, so if two peers want to use it, they can resort in hiding the communication into casual looking data. This problem has become more and more important just in these days, after the international Wassenaar agreement, with which around thirty of the major – with respect to technology – countries in the world decided to apply restrictions in cryptography export similar to the US’s ones.

In a digital world, Steganography and Cryptography are both intended to protect information from unwanted parties. Both Steganography and Cryptography are excellent means by which to accomplish this but neither technology alone is perfect and both can be broken. It is for this reason that most experts would suggest using both to add multiple layers of security. Steganography can be used in a large amount of data formats in the digital world of today. The most popular data formats used are .bmp, .doc, .gif, .jpeg, .mp3, .txt and .wav. Mainly because of their popularity on the Internet and the ease of use of the steganographic tools that use these data formats. These formats are also popular because of the relative ease by which redundant or noisy data can be removed from them and replaced with a hidden message. Steganographic technologies are a very important part of the future of Internet security and privacy on open systems such as the Internet. Steganographic research is primarily driven by the lack of strength in the cryptographic systems on their own and the desire to have complete secrecy in an open-systems environment. Many governments have created laws that either limit the strength of cryptosystems or prohibit them completely. This has been done primarily for fear by law enforcement not to be able to gain intelligence by wiretaps, etc. This unfortunately leaves the majority of the Internet community either with relatively weak and a lot of the times breakable encryption algorithms or none at all. Civil liberties advocates fight this with the argument that “these limitations are an assault on privacy”. This is where Steganography comes in. Steganography can be used to hide important data inside another file so that only the parties intended to get the message even knows a secret message exists.

STEGANOGRAPHY AND CRYPTOGRAPHY

Steganography and cryptography are cousins in spy-craft family. Cryptography scrambles a message so it cannot be understood. Steganography hides the message so it cannot be seen. A message in cipher text for instance might arouse suspicion on the part of the recipient while an “invisible” message created with steganographic methods will not. In this way, we can say that steganography completes cryptography, and actually there are usually two ciphers to break when trying to extract the embedded message: one is the one with which the message was embedded, and the other is the one with which the

message was enciphered.

A BRIEF HISTORY OF STEGANOGRAPHY

The earliest recordings of Steganography were by the Greek historian Herodotus in his chronicles known as “Histories” and date back to around 440 BC. Herodotus recorded two stories of Steganographic techniques during this time in Greece[2]. The first stated that King Darius of Susa shaved the head of one of his prisoners and wrote a secret message on his scalp. When the prisoner’s hair grew back, he was sent to the Kings son in law Aristogoras in Miletus undetected. The second story also came from Herodotus, which claims that a soldier named Demeratus needed to send a message to Sparta that Xerxes intended to invade Greece. Back then, the writing medium was text written on wax-covered tablets. Demeratus removed the wax from the tablet, wrote the secret message on the underlying wood, recovered the tablet with wax to make it appear as a blank tablet and finally sent the document without being detected.

Romans used invisible inks, which were based on natural substances such as fruit juices and milk. This was accomplished by heating the hidden text, thus revealing its contents. Invisible inks have become much more advanced and are still in limited use today. During the 15th and 16th centuries, many writers including Johannes Trithemius (author of Steganographia) and Gaspari Schotti (author or Steganographica) wrote on Steganagraphic techniques such as coding techniques for text, invisible inks, and incorporating hidden messages in music.

Between 1883 and 1907, further development can be attributed to the publications of Auguste Kerckhoff (author of Cryptographic Militaire) and Charles Briquet (author of Les Filigranes). These books were mostly about Cryptography, but both can be attributed to the foundation of some steganographic systems and more significantly to watermarking techniques.

Concepts such as null ciphers (taking the 3rd letter from each word in a harmless message to create a hidden message, etc), image substitution and microdot (taking data such as pictures and reducing it to the size of a large period on a piece of paper) were introduced and embraced as great steganographic techniques.

In the recent digital world of today, namely 1992 to present, Steganography is being used all over the world on computer systems. Many tools and technologies have been created that take advantage of old steganographic techniques such as null ciphers, coding in images, audio, video and microdot. With the research this topic is now getting we will see a lot of great applications for Steganography in the near future.

3. Some definitions

Some definitions common to the steganography field:

Cover medium: This is the medium in which we want to hide data, it can be an innocent looking piece of information for steganography, or some important medium that must be protected for copyright or integrity reasons.

Embedded message: This is the hidden message we want to put in the cover. It can be some data for steganography and some copyright informations or added content for digital watermarking.

Stegokey: This is represented by some secret information, which is needed in order to extract the embedded message from the stego-medium

Stego-medium: This is the final piece of information that the casual observer can see.

We can define this simple formula:

Cover-medium + embedded-message = stego-message

THE BASIC METHOD BEHIND STEGANOGRAPHY

Password (key)

Stego-media

Steganography Application Tool

Image or Sound File

File to Hide

-Image

-Text

-Any File

SENDING A STEGANOGRAPHIC MESSAGE:

First we need to select a carrier file.

Then we need to choose the method of steganography used.

Choose a program to hide message in carrier file.

Communicate the chosen method to the receiver using a different channel.

Embed the message in carrier file, if possible, encrypt it.

Choose a regular medium to transfer the file.

In practice there are three types of steganography protocols used:

Pure steganography,

Secrete key steganography,

Public key steganography.

Pure steganography:

Pure steganography is defined as a steganographic system where there is no need to exchange any password that is stego-key in order for the receiver to read the message.This method of Steganography is the least secure means by which to communicate secretly because the sender and receiver can rely only upon the presumption that no other parties are aware of this secret message.

Secrete key steganography:

Secret Key Steganography is defined as a steganographic system that requires the exchange of a secret key (stego-key) prior to communication.only the persons who know this secrete key can reverse the process using stego-key and read the message. The benefit to Secret Key Steganography is even if it is intercepted, only parties who know the secret key can extract the secret message.

Public key steganography:

Public Key Steganography is defined as a steganographic system that uses a public key and a private key to secure the communication between the parties wanting to communicate secretly. The sender will use the public key during the encoding process and only the private key, which has a direct mathematical relationship with the public key can be used by the receiver to read the message. It also has multiple levels of security in that unwanted parties must first suspect the use of steganography and then they would have to find a way to crack the algorithm used by the public key system before they could intercept the secret message.

STEGANOGRAPHY UNDER VARIOUS MEDIA

Often, although it is not necessary, the hidden messages will be encrypted. This meets a requirement posed by the “Kerckhoff principle” in cryptography. This principle states that the security of the system has to be based on the assumption that the enemy has full knowledge of the design and implementation details of the steganographic system. The only missing information for the enemy is a short, easily exchangeable random number sequence, the secret key. Without this secret key, the enemy should not have the chance to even suspect that on an observed communication channel, hidden communication is taking place. When embedding data it is important to remember the following restrictions and features:

The cover data should not be significantly degraded by the embedded data, and the

embedded data should be a imperceptible as possible.

The embedded data should be directly encoded into the media, rather than into a

header or wrapper, to maintain data consistency across formats.

The embedded data should be as immune as possible to modifications from intelligent attacks or anticipated manipulations such as filtering and resampling.

Some distortion or degradation of the embedded data can be expected when the cover data is modified. To minimize this, error correcting codes should be used.

The embedded data should be self clocking or arbitrarily re-entrant. This ensures that the embedded data can still be extracted when only portions of the cover data is available.

Steganography works has been carried out on different transmission mediums like text, audio, video, images.

STEGANOGRAPHY IN TEXT

Hiding in Text

The steganographic principles can also be applied to a normal text file. Sometimes, this is done by hiding the message in the blank spaces between words. The message is separated between the lsbs of the binary code for the empty space throughout the text. Once again, this method requires the text you are sending to be considerably longer than the message you are hiding within it. You can also hide messages in PDF documents and in a variety of other standards, depending on which program you wish to use.

The most difficult kind of steganography is the test steganography because due to the lack of redundant information in the text when compared to image or audio file. The advantages of the text steganography over other mediums are its smaller memory occupation an simpler communication.

The block diagram of generic text steganograhic system is:

Cover Text

Secret Message

Embedding Algorithm

Communication Channel

Secret Message

Secret Key

Extracting Algorithm

Stego Text

Stego Text

Here a message is embedded in a text through an embedding algorithm. Then the message is passed to receiver over a channel and is extracted by using a secrete key by the receiver.

Text steganography is broadly divided into 3 types

Format based,

Random and statistical generations

Linguistic method

FORMAT BASED:

Format-based methods use and change the formatting ofthe cover-text to hide data. They do not change any word or sentence, so it does not harm the ‘value’ of the cover-text.In this method extra white spaces are added into the text to hide information. These white spaces can be added after end of each word, sentence or paragraph. A single space is interpreted as “0” and two consecutive spaces are interpreted as “1”. Although a little amount of data can be hidden ina document, this method can be applied to almost all kindsof text without revealing the existence of the hidden data. Another two format-based methods are word shifting and line shifting.

Word shift coding

In word-shift coding, code words are coded into a document by shifting the horizontal locations of words within text lines, while maintaining a natural spacing appearance. The method, of course, is only applicable to documents with variable spacing between adjacent words, such as in documents that have been text-justified. As a result of this variable spacing, it is necessary to have the original image, or to at least know the spacing between words in the un-encoded document. Word-shift coding should be less visible to the reader than line-shift coding, since the spacing between adjacent words on a line is often shifted to support text justification.

Here the horizontal alignments of some words are shifted by changing distances between words to embed information . These changes are hard to interpret because varying distances between words are very common in documents. Another method of hiding information in manipulation of white spaces between words and paragraph.

Line shift coding:

Here vertical alignments of some lines of the text are shifted to create a unique hidden shape to embeda message in it.

In this method, text lines are vertically shifted to encode the document uniquely. Encoding and decoding can generally be applied either to the format file of a document, or the bitmap of a page image. By moving every second line of document either 1/300 of an inch up or down, Brassil et al. Found that line-shift coding worked particularly well, and documents could still be completely decoded, even after the tenth photocopy. It is probably the most visible text coding technique to the reader.

Feature coding:

This is applied either to the bitmap image of a document, or to a format file. In feature coding, certain text features are altered, or not altered, depending on the codeword. Generally, before encoding, feature randomization takes place. That is, character end-line lengths would be randomly lengthened or shortened, then altered again to encode the specific data. This removes the possibility of visual decoding, as the original end-line lengths would not be known. Alternative, interesting text-coding methods are provided by Bender. The three major methods of encoding data:

Open space methods, similar to the ones suggested by Brassil.

Syntactic methods, that utilize punctuation and contractions.

Semantic methods, that encode using manipulation of the words themselves.

Other methods of syntactic encoding include the controlled use of contractions and abbreviations. Although such syntactic encoding is very possible in the English language, the amount of data that could be encoded would be very low, somewhere in the order of a several bits per kilobyte of text.

RANDOM AND STATISTICAL GENERATION METHODS:

This method is used to generate cover text according to the statistical properties of the language. These methods use example grammars to produce cover-text in a certain natural language. A probabilistic context-free grammar (PCFG) is a commonly usedlanguage model where each transformation rule of a contextfreegrammar has a probability associated with it . The sentences are constructed according to the secrete message to be hide in it. The quality of the generated stego message depends directly on the quality of the grammar used. Another method is to generate words having same statistical properties like word length and letter frequency as the original message[6].

LINGUSITICS METHOD:

Syntactic method is the linguistics steganography method where some punctuation sign like comma(,) and full stop(.) are placed in the proper places to embed the data. This needs proper identification of places where the signs can be inserted properly. Another linguistics method is the semantic method where, the synonym of words for some pre-selected are used. The words are replaced by their synonyms to hide information in it.

OTHER METHODS:

Many researchers have suggested many methods for hiding information in text besides above three categories such as feature coding, text steganography by specific characters in words, abbreviations etc. or by changing words spelling.

B. STEGANOGRAPHY IN IMAGES

Digital images (those that appear on your computer) are broken up into pixels – tiny dots with a specific colour that together make up the image you can see. For images, steganographers encode the message into the pixel LSB. This means that, to the human eye, the colour of the pixel (represented by binary code to the computer) does not change. The hidden message can be withdrawn from the picture provided you know: a) that there is a message in the image b) that you use the same steganographic program for decoding as the one used to hide the message.

The carrier image

A fragment from the photo, representing different values of individual pixels

The top two rows of the palette have the word ‘OK’ embedded into the LSBs

The resulting steganographic image

Steganographic images are detectable. They do not appear any different to the human eye, but computers, programmed to look for them, can notice slight colour variations when modifying the LSB. It is for this reason that many security experts doubt the practicality of using steganography. If this proves to be the case, other methods, like encryption, can also be used. Some programs will not only code your message into an image, but will encrypt it, too. The steganalysts (those responsible for decoding steganographic messages) would still have to break the encryption in the message extracted from the image.

Image steganography is about exploiting the limited powers of the human visual system (HVS). Within reason, any plain text, ciphertext, other images, or anything that can be embedded in a bit stream can be hidden in an image. Image steganography has come quite far in recent years with the development of fast, powerful graphical computers, and steganographic software is now readily available over the Internet for everyday users.

Encoding in an image

Assume a large number of color combinations

Agree upon a repeatable random sequence of pixel locations

While (more bits to encode)

Select the next pixel location

Get the next bit from the message

Set the low-order bit of a color component of the sample at the location to the current bit value of the message

Example

Message = 0001 1010 1101 0111

Image bit stream = …. 01101110 ….

New bit stream = …. 01101111 ….

Color intensity change = 1/255 of its range!

Decoding from an Image

While (there are more bits in the message)

Generate the next pixel location to examine

Extract the bit from the low-order position of the color component

Append the bit to the message bit stream, subdividing when appropriate boundaries occur

Boundaries may not be byte-sized. Messages can be images, sounds, text, programs, or data!

Concealment in digital images

Information can be hidden many different ways in images. To hide information, straight message insertion may encode every bit of information in the message or selectively embed the message in “noisy” areas that draw less attention- those areas where there is a great deal of natural color variation. The message may also be scattered randomly throughout the image. Redundant pattern encoding “wallpapers” the cover image with the message.

A number of ways exist to hide information in digital images. Common approaches include:

Least significant bit (LSB) insertion.

Masking and filtering.

Algorithms and transformations.

Least significant bit insertion

The least significant bit insertion method is probably the most well known image steganography technique. It is a common, simple approach to embedding information in a graphical image file. Unfortunately, it is extremely vulnerable to attacks, such as image manipulation. A simple conversion from a GIF or BMP format to a lossy compression format such as JPEG can destroy the hidden information in the image.

When applying LSB techniques to each byte of a 24-bit image, three bits can be encoded into each pixel. ( As each pixel is represented by three bytes.) Any changes in the pixel bits will be indiscernible to the human eye. For example, the letter A can be hidden in three pixels. Assume the original three pixels are represented by the three 24-bit words below:

(00100111 11101001 11001000)

(00100111 11001000 11101001)

(11001000 00100111 11101001)

The binary value for the letter A is (10000011). Inserting the binary value of A into the three pixels, starting from the top left byte, would result in:

(0010011111101000 11001000)

(00100110 11001000 11101000)

(11001000 0010011111101001)

The emphasized bits are the only bits that actually changed. The main advantage of LSB insertion is that data can be hidden in the least and second to least bits and still the human eye would be unable to notice it.

Image compression:

Image compression offers a solution to large image files. Two kinds of image compression are lossless and lossy compression. Both methods save storage space but have differing effects on any uncompressed hidden data in the image.

Lossy compression, as typified by JPEG (Joint Photographic Experts Group) format files, offers high compression, but may not maintain the original image’s integrity. This can impact negatively on any hidden data in the image. This is due to the lossy compression algorithm, which may “lose” unnecessary image data, providing a close approximation to high-quality digital images, but not an exact duplicate lossy compression is frequently used on true-color images, as it offers high compression rates.

Lossless compression maintains the original image data exactly; hence it is preferred when the original information must remain intact. It is thus more favored by steganographic techniques. Unfortunately, lossless compression does not offer such high compression rates as lossy compression like GIF (Graphics Interchange Format) and Microsoft’s BMP (Bitmap) format.

The image downgrading problem:

In multilevel security systems, such as the ones used by the army, it sometimes becomes necessary to declassify some information from a high level of access to a lower level. Unfortunately, downgrading of images can present a problem. Information could be covertly hidden in a “top secret” image for later retrieval when the image is declassified. This problem has been pointed out by Kurak and McHugh and is well demonstrated by the following sets of photographs, which illustrate how well data can be hidden. As can be seen in figures 1 and 2 on the following pages, the image of the Pentagon on the right of figure 1 is hidden in the picture of the original chapel on the left, giving the contaminated chapel picture and the encoded Pentagon picture below.

Fig 1: original image Fig 2: Encoded Pentagon

Masking and Filtering

Masking and filtering techniques usually restricted to 24-bit and tray-scale images hide information by marking an image, in a manner similar to paper watermarks. Watermarking techniques may be applied without fear of image destruction due to lossy compression because they are more integrated into the image.

Visible watermarks are not steganography by definition. The difference is primarily one of intent. Traditional steganography conceals information; watermarks extend information and become an attribute of the cover image. Digital watermarks may include such information as copyright, ownership, or license. In steganography, the object of communication is the hidden message. In digital watermarking, the object of communication is the cover.

To create a watermarked image, we increase the luminance of the masked area by 15 percent. If we were to change the luminance by a smaller percentage, the mask would be undetected by the human eye. Now we can use the watermarked image to hide plaintext or encoded information.

Masking is more robust than LSB insertion with respect to compression, cropping and some image processing. Masking techniques embed information in more significant areas so that the hidden message is more integral to the cover image than just hiding it in the “noise” level. This makes it more suitable than LSB with lossy JPEG images.

Algorithms and Transformations

LSB manipulation is a quick and easy way to hide information but is vulnerable to small changes resulting from image processing or lossy compression. Such compression is a key advantage that JPEG images have over other formats. High quality images can be stored in relatively small files using JPEG compression method.

One steganographic method that integrates the compression algorithm for hiding the information is Jpeg-Jsteg.

Jpeg-Jsteg creates a JPEG stego image from the input of a message to be hidden and a lossless cover mage.

Another method used in Patchwork and similar techniques is the redundant pattern encoding. Here the hidden information is scattered throughout the cover mage. These approaches may help protect against image processing such as cropping and rotations and they hide information more thoroughly than by simply masking. They also support image manipulation more readily than tools that rely on LSB. In using redundant pattern encoding, you must trade off message size against robustness. A large message may be embedded only once because it would occupy a much greater portion of the image area.

Other techniques encrypt and scatter the hidden data throughout an image. Scattering the message makes it appear more like noise. Proponents of this approach assume that even if the message bits are extracted, they will be useless without the algorithm and stego-key to decode them.

Scattering and encryption helps protect against hidden message extraction but not against message destruction through image processing. A scattered message in the image’s LSBs is still as vulnerable to destruction from lossy compression and image processing, as is a clear text message inserted in the LSBs.

STEGANOGRAPHY IN AUDIO

Hiding in Audio:

Steganography can also be applied to audio files. Take, for example, the MP3 format. It is a method of compressing a natural audio file to a much smaller size. This is achieved by removing the audio frequency that the human ear cannot pick up: our ears can only hear sounds of a particular range of frequency. Natural audio, however, records a much larger frequency, and removing the excess sounds does not significantly change the quality of the audio (to our ears). This is how MP3 files are made. Audio steganography adds the message to the unused frequency in them, and – once again – the human ear is unable to detect the difference in the sound quality.

Here’s a frequency diagram of an audio transcript

And here is the same piece of audio, with a message hidden within the frequency

An Overview of Steganography for the Computer Forensics Examiner

And whereas you may be able to detect the difference by looking at the diagram, it is much more difficult to hear.

Steganography in audio:

Because of the range of the human auditory system (HAS), data hiding in audio signals is especially challenging. When performing data hiding in audio, one must exploit the weaknesses of the HA, while at the same time being aware of the extreme sensitivity of the human auditory system.

Audio environment

When working with transmitted audio signals, one should bear in mind two main considerations. First, the means of audio storage, or digital representation of the audio, and second, the transmission medium the signal might take.

Digital representation

Digital audio files generally have two primary characteristics:

Sample quantization method:

The most popular format for representing samples of high-quality digital audio is a 16-bit linear quantisation, which is used by WAV (Windows Audio-Visual) and AIFF (Audio Interchange File Format).Some signal distortion is introduced by this format.

Temporal sampling rate:

The most popular temporal sampling rates for audio include 8kHz (kilohertz, 9.6kHz,10kHz, 12kHz, 16kHz, 22.05kHz and 44.1kHz.

Sampling rate puts an upper bound on the usable portion of the frequency range. Generally, usable data space increases at least linearly with increased sampling rate.

Another digital representation that should be considered is the ISO MPEG Audio format, a perceptual encoding standard. This format drastically changes the statistics of the signal by encoding only the parts the listener perceives, thus maintaining the sound, but changing the signal.

Transmission medium:

The transmission medium, or transmission environment, of an audio signal refers to the environments the signal might go through on its way from encoder to decoder.

There are four transmission mediums available:

Digital end-to-end environment:

If a sound file is copied directly from machine to machine, but never modified, then it will go through this environment. As a result, the sampling will be exactly the same between the encoder and decoder. Very little constraints are put on data-hiding in this environment.

Increased/decreased resampling environment:

A signal is resampled to a higher or lower sampling rate, but remains digital throughout. Although the absolute magnitude and phase of most of the signal are preserved, the temporal characteristics of the signal are changed.

Analog transmission and resampling:

It occurs when a signal is converted to an analog state, played on a relatively clean analog line, and resampled. Absolute signal magnitude, sample quantization and temporal sampling rate are not preserved. In general, phase will be preserved.

”Over the air” environment:

This occurs when the signal is “played into the air” and “resample with a microphone”. The signal will be subjected to possible unknown nonlinear modifications causing phase changes, amplitude changes, drifting of different frequency components, echoes, etc.

METHODS OF AUDIO DATA HIDING:

Low-bit encoding :

Similarly to how data was stored in the least-significant bit of images, binary data can be stored in the least-significant bit of audio files. Ideally the channel capacity is 1kb per second per kilohertz, so for example, the channel capacity would be 44kbps in a 44kHz sampled sequence. Unfortunately, this introduces audible noise. Of course, the primary disadvantage of this method is its poor immunity to manipulation. Factors such as channel noise and resampling can easily destroy the hidden signal.

Phase coding :

The phase coding method works by substituting the phase of an initial audio segment with a reference phase that represents the data.

The procedure for phase coding is as follows:

The original sound sequence is broken into a series of N short segments.

A discrete Fourier transform (DFT) is applied to each segment, to break create a matrix of the phase and magnitude.

The phase difference between each adjacent segment is calculated.

For segment S0, the first segment, an artificial absolute phase p0 is created.

For all other segments, new phase frames are created.

The new phase and original magnitude are combined to get a new segment, Sn.

Finally, the new segments are concatenated to create the encoded output.

Spread spectrum :

Most communication channels try to concentrate audio data in as narrow a region of the frequency spectrum as possible in order to conserve bandwidth and power. When using a spread spectrum technique, however, the encoded data is spread across as much of the frequency spectrum as possible.

Direct Sequence Spread Spectrum (DSSS) encoding, spreads the signal by multiplying it by a certain maximal length pseudorandom sequence, known as a chip. The sampling rate of the host signal is used as the chip rate for coding. The calculation of the start and end quanta for phase locking purposes is taken care of by the discrete, sampled nature of the host signal. As a result, a higher chip rate and therefore a higher associated data rate, is possible.

Echo data hiding:

Echo data hiding embeds data into a host signal by introducing an echo. The data are hidden by varying three parameters of the echo:

1) Initial amplitude,

2) Decay rate, and

3) Offset or delay.

As the offset between the original and the echo decreases, the two signals blend. At a certain point, the human ear cannot distinguish between the two signals, and the echo is merely heard as added resonance. It depends on factors such as the quality of the original recording, the type of sound, and the listener.

6. APPLICATIONS

6.1 DIGITAL WATER MARKING is an application of Steganography:

Steganography is used by some modern printers, including HP and Xerox brand color laser printers. Tiny yellow dots are added to each page. The dots are barely visible and contain encoded printer serial numbers, as well as date and time stamps. Steganography can be used for digital watermarking, where a message (being simply an identifier) is hidden in an image.

What is watermarking?

The process of embedding information into another object/signal can be termed as watermarking. it is mostly agreed that the watermark is one, which is imperceptibly added to the cover-signal in order to convey the hidden data. 

Digital watermarking can be classified as:

Visible

Invisible watermarking

Visible water marking:

Visible watermarks change the signal altogether such that the watermarked signal is totally different from the actual signal, e.g., adding an image as a watermark to another image.

Visible watermarks can be used in following cases :

Visible watermarking for enhanced copyright protection.

Visible watermarking used to indicate ownership originals.

Invisible water marking:

Invisible watermarks do not change the signal to a perceptually great extent, i.e., there are only minor variations in the output signal.

An example of an invisible watermark is when some bits are added to an image modifying only its least significant bits. Invisible watermarks that are unknown to the end user are steganographic. While the addition of the hidden message to the signal does not restrict that signal’s use, it provides a mechanism to track the signal to the original owner.

Differences between visible and invisible water marking:

Visibility is a term associated with the perception of the human eye. A watermarked image in which the watermark is imperceptible, or the watermarked image is visually identical to its orginal constitutes a invisible watermarking. Examples include images distrubuted over internet with watermarks embedded in them for copyright protection. Those which fail can be classified as visible watermarks. 

Difference between steganography and watermarking

The main goal of steganography is to hide a message in some audio or video (cover) data , to obtain new data , practically indistinguishable from data, by people, in such a way that an eavesdropper cannot detect the presence of message in new data.

The main goal of watermarking is to hide a message in some audio or video (cover) data , to obtain new data , practically indistinguishable from data, by people, in such a way that an eavesdropper cannot remove or replace message in new data.

It is also often said that the goal of steganography is to hide a message in one-to-one communications and the goal of watermarking is to hide message in one-to-many communications.

Shortly, one can say that cryptography is about protecting the content of messages, steganography is about concealing its very existence.

Steganography methods usually do not need to provide strong security against removing or modification of the hidden message. Watermarking methods need to to be very robust to attempts to remove or modify a hidden message.

6.2 Other Applications of Water Marking:

1) Automatic monitoring and tracking of copy-write material on WEB. (For example, a robot searches the Web for marked material and thereby identifies potential illegal issues.)

2) Automatic audit of radio transmissions: (A robot can “listen” to a radio station and look for marks, which indicate that a particular piece of music, or advertisement, has been broadcast).

3) Finger printing applications: (Another application is to protect digital media by fingerprinting each copy with the purchaser’s information. If the purchaser makes illegitimate copies, these will contain his name.)

6.3. Confidential communication and secret data storing

　

The “secrecy” of the embedded data is essential in this area.

　Historically, steganography have been approached in this area. Steganography provides us with:

   (A) Potential capability to hide the existence of confidential data

   (B) Hardness of detecting the hidden (i.e., embedded) data

   (C) Strengthening of the secrecy of the encrypted data

In practice, when you use some steganography, you must first select a vessel data according to the size of the embedding data. The vessel should be innocuous. Then, you embed the confidential data by using an embedding program (which is one component of the steganography software) together with some key. When extracting, you (or your party) use an extracting program (another component) to recover the embedded data by the same key ( “common key” in terms of cryptography). In this case you need a “key negotiation” before you start communication.

Attaching a stego file to an e-mail message is the simplest example in this application area. But you and your party must do a “sending-and-receiving” action that could be noticed by a third party. So, e-mailing is not a completely secret communication method.

6.4 Media Database systems

　

In this application area of steganography secrecy is not important, but unifying two types of data into one is the most important. 

　

Media data (photo picture, movie, music, etc.) have some association with other information. A photo picture, for instance, may have the following.

  (1) The title of the picture and some physical object information

  (2) The date and the time when the picture was taken

  (3) The camera and the photographer’s information

Formerly, these are annotated beside the each picture in the album.

　Recently, almost all cameras are digitalized. They are cheap in price, easy to use, quick to shoot. They eventually made people feel reluctant to work on annotating each picture. Now, most home PC’s are stuck with the huge amount of photo files. In this situation it is very hard to find a specific shot in the piles of pictures. A “photo album software” may help a little. You can sort the pictures and put a couple of annotation words to each photo. When you want to find a specific picture, you can make a search by keywords for the target picture. However, the annotation data in such software are not unified with the target pictures. Each annotation only has a link to the picture. Therefore, when you transfer the pictures to a different album software, all the annotation data are lost.

　

This problem is technically referred to as “Metadata (e.g., annotation data) in a media database system (a photo album software) are separated from the media data (photo data) in the database managing system (DBMS).” This is a big problem.

　

Steganography can solve this problem because a steganography program unifies two types of data into one by way of embedding operation. So, metadata can easily be transferred from one system to another without hitch. Specifically, you can embed all your good/bad memory (of your sight-seeing trip) in each snap shot of the digital photo. You can either send the embedded picture to your friend to extract your memory on his/her PC, or you may keep it silent in your own PC to enjoy extracting the memory ten years after.

6.5. Access control system for digital content distribution

In this area embedded data is “hidden”, but is “explained” to publicize the content.

Today, digital contents are getting more and more commonly distributed by Internet than ever before. For example, music companies release new albums on their Webpage in a free or charged manner. However, in this case, all the contents are equally distributed to the people who accessed the page. So, an ordinary Web distribution scheme is not suited for a “case-by-case” and “selective” distribution. Of course it is always possible to attach digital content to e-mail messages and send to the customers. But it will takes a lot of cost in time and labor.

If you have some valuable content, which you think it is okay to provide others if they really need it, and if it is possible to upload such content on the Web in some covert manner. And if you can issue a special “access key” to extract the content selectively, you will be very happy about it. A steganographic scheme can help realize a this type of system.

We have developed a prototype of an “Access Control System” for digital content distribution through Internet. The following steps explain the scheme.

(1) A content owner classify his/her digital contents in a folder-by-folder manner, and embed the whole folders in some large vessel according to a steganographic method using folder access keys, and upload the embedded vessel (stego data) on his/her own Webpage.

(2)  On that Webpage the owner explains the contents in depth and publicize worldwide. The contact information to the owner (post mail address, e-mail address, phone number, etc.) will be posted there.

(3) The owner may receive an access-request from a customer who watched that Webpage. In that case, the owner may (or may not) creates an access key and provide it to the customer (free or charged).

6.6. Alleged use by terrorists

When one considers that messages could be encrypted steganographically in e-mail messages, particularly e-mail spam, the notion of junk e-mail takes on a whole new light. Coupled with the “chaffing and winnowing” technique, a sender could get messages out and cover their tracks all at once.

An example showing how terrorists may useforum avatars to send hidden messages. This avatar contains the message “Boss said that we should blow up the bridge at midnight.”

7. CONCLUSION

In this paper, we take an introductory look at steganography. Historical detail is discussed. Several methods for hiding data in text, images, and audio are described, with appropriate introductions to the environments of each medium, as well as the strengths and weaknesses of each method. Most data-hiding systems take advantage of human perceptual weaknesses, but have weaknesses of their own. We conclude that for now, it seems that no system of data-hiding is totally immune to attack.

However, steganography has its place in security. It in no way can replace cryptography, but is intended to supplement it. Its application in watermarking and fingerprinting, for use in detection of unauthorized, illegally copied material, is continually being realized and developed. Also, in places where standard cryptography and encryption is outlawed, steganography can be used for covert data transmission. Steganography, formerly just an interest of the military, is now gaining popularity among the masses. Soon, any computer user will be able to put his own watermark on his artistic creations.

Steganography and digital watermarking are undergoing a development process similar to that of encryption. Steganography’s niche in security is to supplement cryptography and not to replace it. There is a continuous invention of new techniques for steganography followed by successful breakings and new improvements of them. Then we showed the different techniques invented, from the simplest to the more complex ones, trying to evaluate them under many points of view. Major emphasis was put on data hiding in images, for the techniques involved are usually more mature than the corresponding ones for other kinds of informations. Image encoding algorithms can also be representative for manipulation of other types of media like voice, text, binary files, binary files, communication channels etc.