Steganography is the term for data that is hidden within other data. An additional layer of security for data protection can be achieved by combining steganography, an encryption technique, with cryptography.

Steganography techniques are useful for audio, video, and image files. While it is often used in visuals, steganography is usually written in characters with hash marks. In any case, steganography makes it easier for unauthorized viewers to see copyrighted content while simultaneously protecting it from misuse.

Steganography is intended to be concealed from third parties, in comparison with cryptography, which is intended to be incomprehensible to an unauthorised third party. The secret information has to be encrypted, which can be challenging, in addition to being identified, which is a difficult attempt in and of itself.

In general, the information hiding procedure extracts redundant bits from coverobject. The process includes two steps which are as follows −

• Recognition of redundant bits in a cover-object. Redundant bits are those bits that can be changed without corrupting the feature or failure the principle of the cover-object.
• The embedding procedure choose the subset of the redundant bits to be restored with data from a secret message. The stego-object is produced by restoring the selected redundant bits with message bits.

Types of Steganography

Steganography is a way of hiding not just information but also the transmission element of secret information. Steganography hides confidential data in a different file so that only the intended receiver knows of its availability.

Data security in the past involved hiding information on the scalps of slaves, writing tables, rabbit stomachs, and the backs of wax. However, some people these days use the medium to send information in the form of text, photos, videos, and audio.

Confidential information can be securely transmitted, and multimedia elements like music, video, and photos can be used as cover sources for hiding information.

There are different types of steganography present −

Text Steganography

It involves encrypting text files with hidden data. Using this method, the secret information is hidden behind every nth character in a text message. There are numerous methods for concealing data in text files.

Approaches of Text Steganography

There are various approaches of text steganography which are as follows −

• Line Shift − In this method, secret message is private by vertically changing the text lines to some degree. A line decided has two clear control lines one on side of it for identifying the direction of movement of the marked line. It can hide bit 0, a line is changed up and to hide bit 1, the line is changed down.

  Determination of whether the line has been changed up or down is completed by computing the distance of the centroid of apparent line and its control lines. If the text is retyped or if a character recognition program (OCR) is utilized, the hidden data can get destroyed.

• White Steg − This technique uses white spaces for concealing a secret message. There are three methods of hiding information utilizing white spaces.

  In Inter Sentence Spacing, it can place individual space to hide bit 0 and two spaces to hide bit 1 at the end of each removing character. In End of Line Spaces, fixed number of spaces is added at the end of each line.

  For instance, two spaces to encrypt one bit per line, four spaces to encrypt two bits and so on. In Inter Word Spacing approach, one space after a word defines bit 0 and two spaces after a word define bit 1. But, uncertain use of white space is not clear.

• Spam Text − HTML and XML files can also be used to protect bits. If there are different starting and closing tags, bit 0 is interpreted and if an individual tag can be used for starting and closing it, therefore bit 1 is interpreted.

  In another approach, bit 0 is defined by a lack of space in a tag and bit 1 is defined by locating a space within a tag.

• Word Shift − In this approach, private message is hidden by changing the words horizontally, such as left or right to define bit 0 or 1 respectively.

  Words shift are identified using correlation method that consider a profile as a waveform and determines whether it originated from a waveform whose central block has been changed left or right.

  This approach can be recognized less, because change of distance among words to fill a line is completely frequent. But if someone understands the algorithm of distances, it can compare the stego text with the algorithm and acquire the hidden content by utilizing the difference. It can also, retyping or using OCR programs destroys the hidden data.

• SMS-Texting − SMS-Texting language is a set of abbreviated words used in SMS. It can hide binary information by utilizing full form of word or its abbreviated form. A codebook is create which includes words and their correlating abbreviated forms.

Image Steganography

It is defined as the process of concealing information by using a picture as a cover object. Pixel intensities are used in image steganography to hide data.

Images are a commonly used cover source in digital steganography because a computer description of an image contains multiple bits.

The following are some of the terms used in image steganography −

• Cover-Image − The original image that serves as an entry point for information that is hidden.
• Message − Real data that can be hidden behind pictures. The message can be sent as an image or as plaintext.
• Stego-image − IT is created when a message is embedded into a cover image.
• Stego-Key − A key used to embed or extract messages from stego-images and cover-images.

Audio Steganography

The technology for information embedding in an audio channel is called audio steganography. Digital copyright protection is one application for it.

One method of hiding a piece of information [message] within another piece of information [carrier] is watermarking. Usually, it is used for audio clip applications, among other applications.

Video Steganography

It is a technique that hides documents or other data in computer video formats. This technique uses video, which is a collection of images, as a carrier for hiding information.

Discrete cosine transforms, or DCTs, typically create values (such 8.667 to 9) that can be used to mask data that is invisible to the human eye in each of the video”s pictures. The video steganography layout uses H.264, Mp4, MPEG, and AVI.

Network Steganography

It is also known as protocol steganography, involves hiding data by designing a network protocol that uses cover objects like TCP, UDP, ICMP, IP, etc. Steganography can be used in secret channels which are present in the OSI layer network model.

Tools of Steganography

Tools for steganography are used for hiding documents within various types of data. These are the instruments required for steganography to be used. With the help of S-Tools, it can function with steganography in both audio and visual formats.

S-Tools can be used to hide several files inside of a single object. First, each file is compressed independently and saved under its own name. In order to make decryption hard S-Tools is able to prefix the stored data with some random garbage.

There are some tools used for steganography −

• teganos II Security Suite − Steganos is a suite of Win 95/98/NT software that has been completely redesigned with the intention of protecting data. Steganos II need strong encryption and steganographic techniques to hide information in graphic, sound, text, and HTML files. It involves new features such as ”InKA” (Invisible Key Agreement) an implementation of public key steganography, disk encryption, advanced password administration tools, a “Zero-Emission-Pad” text editor to combat tempest attacks, a data shredder, and the “SysLock” function that efficiently locks access to the PC when it can away.
• S-Mail − S-Mail is a program that runs under all versions of Windows and DOS that need strong encryption and compression to hide document in EXE and DLL document. It takes measures to provide that pattern or ID string scanners do not identfy its hiding scheme.
• Stealth − Stealth is a simple filter for PGP, which strips off all recognizing header data to leave only the encrypted information in a format suitable for steganographic use. That is, the data can be hidden in images, audio files, text files, CAD files, and some other file type that can include random information, and then sent to another person who can retrieve the information from the file, connect headers, and PGP decrypt it.
• Invisible Secrets Pro − Invisible Secrets Pro encrypts and hides documents in JPEG, PNG, BMP, HTML and WAV. It also offers strong encryption (such as Blowfish, Twofish, RC4, Cast128, and GOST), a shredder, and a password manager and generator.
• S-Tools in sound − Sound samples in Windows WAV document can be either 8 bits (range 0-255) or 16 bits (range 0- 65535). S-Tools distribute the bit design of the coded message document across the Least Significant Bits of the sample.

Approaches

Need for Steganography

The following are some requirements for steganography −

• Invisibility − The first requirement for a steganographic algorithm is its invisibility, as the secret of steganography”s strength is its capacity to evade detection by the naked eye. The idea is that an image may look to have been altered, as the algorithm is negotiable.
• Payload capacity − Steganography requires a sufficient amount of installing capacity because its purpose is a hidden link, but watermarking just requires a tiny quantity of copyright information to be embedded.
• Robustness against statistical attacks − The process of detecting secret data using statistical tests on image data is known as statistical steganalysis. Some steganographic methods leave behind a “signature” when they embed data, which is easily recognised using statistical analysis. A steganographic technique should not leave an image with a mark that is statistically significant so that it can escape detection by a warden.
• Robustness against image manipulation − When a stego image is connected through trusted networks, an active warden can modify the image in an effort to remove hidden information. Before the image reaches its destination, it can be cropped or rotated as part of image editing. These changes have the power to destroy the hidden message because of how the message is embedded.
• Independent of file format − Given the wide range of picture file formats that are used online, it can seem odd that two parties are always connected by the same file format. This gives powerful steganographic algorithms the capacity to embed data in any kind of file. This also addresses the problem of not always being able to find the ideal image in the ideal format at the ideal time to serve as a cover image.
• Unsuspicious files − This condition include some characteristics of a steganographic algorithm that can result in images that are not used generally and can generate suspicion. Abnormal file size, for example, is one feature of an image that can result in more investigation of the image by a warden.

Application of Steganography

Steganography has multiple applications, which include the following −

• Digital Watermarking − Digital watermarking is the procedure of embedding data into a digital signal in a way that is complex to delete. The signal can be audio, pictures or video.

  For example, if the signal is copied, and then the data is also carried in the copy. A signal can carry several multiple watermarks at the same time.

• Visible Watermarking − In this visible watermarking, the information is visible in the picture or video. Generally, the information is text or a logo which recognizes the owner of the media. When a television broadcaster insert its logo to the corner of transmitted video, and this is also a visible watermark.

• Invisible Watermarking − In this invisible watermarking, information is inserted as digital data to audio, picture or video, but it cannot be perceived as such (although it can be possible to recognize that some amount of data is hidden).

  The watermark can be pre-determined for extensive use and is therefore create simply to fetch or it can be a form of Steganography, where a party connects a hidden message installed in the digital signal.

  In invisible watermarking, the goals is to connect ownership or other descriptive data to the signal in an approach that is complex to remove. It is also applicable to use hidden embedded data as a means of covert connection between individuals.

Difference between Steganography and Cryptography

A table describing the key differences between cryptography and steganography is given below −

Advantages

The advantage of steganography is as follows −

• The advantage of steganography is that messages do not send consideration to themselves. Clearly detectable encrypted message no matter how tough will stimulate suspicion, and may in themselves be compromising in countries where encryption is illegitimate.
• In steganography, cryptography secures the contents of a message, steganography can be said to secure both messages and connecting parties.
• This approach featured security, capacity, and robustness, the three needed element of steganography that creates it beneficial in hidden exchange of data through text files and creating secret communication.
• There are some important files carrying confidential data can be in the server in and encrypted form and No intruder can receive some beneficial information from the initial file during transmit.
• With the need of Steganography Corporation government and law enforcement agencies can connect privately.
• The major objective of steganography is to connect privately in a completely imperceptible aspect and to prevent drawing uncertainty to the transmission of a hidden information. It is not to maintain others from understanding the hidden data, but it is to maintain others from thinking that the data even exists. If a steganography approach generates someone to suspect the carrier medium, thus the method has unsuccessful.
• The advantage of steganography is that it can be generally used to secretly send messages without the case of the transmission being found. By using encryption, it can recognize the sender and the receiver.
• Steganography has a double component of protection such as first, the file itself is secret and second, the data in it is encoded.

Disadvantages of Steganography

The disadvantage of Steganography is as follows −

• Given the volume of data and the size of the file, one could become suspicious.
• If this approach is gone in the wrong hands such as hackers, terrorist, criminals then this can be very much critical.
• Steganography is not without its disadvantages. However, these can be rectified and once it is performed and it can strengthen the element of steganography.
• Most data hiding approach take advantage of human perceptual deficiency, but they have deficiency of their own. However, these can be independently rectified.
• The major disadvantage of steganography is that, unlike cryptography, it needed a lot of overhead to hide associatively few bits of information. Because the steganographic system is found, it is rendered useless. However, it fares no worse than cryptography and is still the preferred medium.