I, _______________________, declare that this thesis titled, Comparison of Watermarking and Steganography Systems and the work presented in it are my own. I confirm that all information in this document has been obtained and presented in accordance with academic rules. I have acknowledged all main sources of help.
This project analyses different systems or schemes that image steganography and image watermarking uses in order to embed message on images. The approach used comes from a wide overview of both the subjects, steganography and watermarking, and analysing the techniques used to embed information on images individually at first. Steganography has various method of embedding information, technical and linguistic. The various techniques used by steganography are captured in details. They include spatial domain technique, categorised into three classes Least Significant Bit, Pixel Value Differencing and Histogram Shifting Method, Transformation Domain Technique, classified into Discrete Cosine Transformation, Discrete Wavelet transformation and Discrete Fourier Transformation, and Distortion technique and masking and filtering.
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Internet security is the process of creating action and rules for protection against internet attacks. It helps in dealing with attacks based on the internet such as, hacking to gain unauthorised access to computer systems, viruses attacks and malicious software which have the capability of damaging data and making systems vulnerable to other threats. Sending data through the internet requires various measures to ensure that it doesnt fall on the wrong hands. Encrypting data is one way to ensure that plain text is translated into cipher text to make sure that the data is only legible for the intended recipient. Decryption is required on the other end to translate the cipher text into plain text to enhance readability. Encryption allows transmission of useless messages to the one who intercepts it.
Firewalls can also be used to deny access networks. They can either be hardware or software. They can prevent information from being stolen or uncovered from networks and attacks from malicious software. Use of anti-malware applications accompanied by good practice from users can prevent electronic mails with sensitive information from being stolen.
Choice of browsers can also be flaws with internet security. Some browsers can enable cyber criminals and hackers attack networks as well as computers. This can be avoided by ensuring that the browser is updated with better and improved security patches that developers release.
Preventing intervening of videos, documents and images as well as digital audio, watermarking and steganography technology helps in reducing the limit of eliminating ability by other parties in deciphering content that one has taken (Ingemar, Mathew, Jeffrey, Jessica, Ton, 2007). Steganography is both an art and science of communication enabling the presence of a message not to be detected. Steganography is mostly used in copyrighting materials. The information being embedded is used in asserting copyright in a document. It protects from detection in while concealing data and against elimination in labelling the documents. Watermarking is marked in the same manner as fingerprinting is done to recognise items since all are marked specifically.
Watermarking involves acts of hiding messages relating to digital signals. Its related to steganography as they both enable hiding messages inside digital signals (Averkiou, M.). Watermarking, attempts in hiding messages relates to the contents of the signal unlike steganography where the signal is used as a medium but they are not related, hence its entirely used as a cover in hiding its existence Steganography and encryption are used in ensuring data confidentiality though there exist a difference (Jonathan et al., 2004). In encryption, someone can know that there is existence of secret communication but they cannot decode the scripted information. Digital signatures are used in allowing asserting authorship in documents (Poornima R., Iswarya R. J., 2013). Its easy to remove the signature with changes invalidating the signature. Steganography is used in provision of secret means of communication that is irremovable without altering embedded data.
This paper analyses image steganography and image watermarking. It discusses the different techniques of embedding the intended information for the two types individually. It will start by discussing methods from a broad point of view then narrow down on image steganography and image watermarking.
Today, the internet provides a channel of data communication which is cheaper and faster in transmitting data over the web. On the other hand, security of data is central to maintain integrity and confidentiality of the data. World Wide Web is used in transmission of data, whether confidential or casual, containing military data, financial transactions, medical diagnosis and personal data which may be purported sensitive (Rai et. al, 2015). Steganography is a mechanism to hide data in a multimedia format file referred to as a carrier. Earlier, cryptography was being used to conceal data by jumbling the content. Unlike cryptography, steganography uses a medium to hide the presence of the information other than to the intended receiver.
In a steganography system, the sender must select a carrier and the message. The applicable and the most effective algorithm is picked to encode the selected message using a secure technique. The Stago file is sent to the receiver through the internet. The receiver uses an extracting algorithm to decode the message in the Stago.
Fig. 1: General Steganography Framework (JALAB et al, 2010).
The analysis of steganography schemes is based on the algorithms they utilize in embedding information on the system and performance system.
Watermarking inscribes messages in a digital signal whose content is related to it. It protects digital images from unauthorized manipulation by inscribing information to verify authenticity and identify the owners. Even if the signal is copied, it is copied with the information in it. It is either visible or invisible. Algorithms are used to embed copyright information in the digital signal as numbers, images or even text. Visible watermarking can be text, image or number. In invisible watermarking, it is implanted into an image in such a manner that it cannot be visualized using human eyes. It can either be robust watermark, fragile, and public and private watermark.
Spatial domain embedment modifies casually selected pixels of one or two subsections of an image. Extraction processes are easy and fast but have weak robust against signal processing attacks. This domain is embedded using two techniques, Local Binary Pattern (LBP) and Least Significant Bit (LSB). Frequent domains on the other hand accommodates more robustness against varying attacks (Alshaikh, 2016). However, it is more complex while being embedded and extracted. Singular Value Decomposition (SVD), Discrete Fourier Transform (DFT), Discrete Wavelet Transform (DWT), and Discrete Cosine Transform (DCT) are the most common techniques for watermarking through frequency domain.
Steganography is classified into two:
2.2.1 Linguistic Steganography
Linguistic steganography is a method that uses language as a concealment. The two main sets include text semagrams and open codes. In open codes, an acquiescently readable script is written which will contain particular words or sentences and selected letters in the script. It can also hide words in reverse or vertical manner (Kipper). Text semagrams on the other hand are about graphical manipulation of the text. The details concealed are very minimal yet visible like spacing which will denote binary values.
2.2.2 Technical Steganography
Technical steganography implements the use tools devices or methods to conceal the intended information. It implements invisible ink, hiding places, microdots and computer-based methods Invisible ink, where the ink needs to be mixed with chemicals, heat or viewed using a special light is one method of technical treatment. Hiding places it the locating of appropriate places to hide the message on a digital signal. Microdots is the shrinking of a printed sheet to a dot equal or less than 0.5 millimetres across, and computer-based methods. It is used to identify automobile or engraved to a DNA strand (Kipper). Computer-based methods involves addition of bits into binary numbers, or even substitution.
2.2.3 Overview of image steganography
There are different steganography algorithms for different image file formats. A computer views an image as a collection of numbers constituting varying light concentrations in different sections of the image (Johnson and Jajodia, 1998). The numbers form a grid to which the particular points are referred to as pixels, presented horizontally in a row manner. The pixels are displayed in bit form by a computer. Bits contained in a colour scheme are referred to as bit depth a pixels bit depth is determined by the number of bits in it. 8 bits is the minimal number contained in a colour scheme (Owens, 2002). This can display only the monochrome and grayscale images. Digital colour images contain bit depth of 24-bits, containing red, green and blue as their basic colours, denoted by 8-bits each. Doing calculations, each pixel will have 256 different amounts of each colour, making a blend of 16 million colours.
It is difficult to transfer large images with bigger bit depth over the web, thus employing techniques to shrink size of the image files. This is by use of mathematical formulas in the analysis of the image, condensing it and producing small image files. The process is referred to as compression (Reference Guide, 1997). Image compression can either be lossy or lossless.
Lossy compression discards excess data from the image file. The difference is not recognizable by human eye since there is close proximity to the original data. Joint Photographic Experts Groups (JPEG) uses image formats from lossy compression processes. However, in lossless compression, instead of removing data from the file image, mathematical formulas are used to represent the image data. The integrity is retained as they are identical. Graphical Interchange Format uses lossless compression
Therefore, image steganography involves obscuring information into a cover image without affecting the display of the image securing the information from access by an unauthorized persons. There are several techniques used in image steganography.
Fig 2: Steganography Techniques (Amritpal and Satinder, 2014)
184.108.40.206 Spatial Domain Method
The data of information to be concealed some bits are converted into the values of the image pixels. It is further classified into:
Least Significant Bit
This is the most commonly used and simplest method of inscribing the information into the cover file. Most images used are 8-bit and 24-bit images; one bit of information is used in 8-bit images and three bits of information are inscribed into the 24-bit. This image is known as stagio image (Akhtar, Johri, and Khan, 2013). This technique is referred to as the least significant bit because it does not change the visual display of the cover image. An example of this technique used in a 24-bit image.
Pixels: (00100111 11101011 11001010)
(00100111 11011000 10101001)
(11001000 00110111 11011001)
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