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Information Hiding Techniques For Steganography


Steganography is the technique of hiding secret data within an ordinary, non-secret, file or message in order to avoid detection; the secret data is then extracted at its destination. The use of steganography can be combined with encryption as an extra step for hiding or protecting data. The word steganography is derived from the Greek words steganos (meaning hidden or covered) and the Greek root graph (meaning to write).




Information Hiding Techniques for Steganography



Forms of steganography have been used for centuries and include almost any technique for hiding a secret message in an otherwise harmless container. For example, using invisible ink to hide secret messages in otherwise inoffensive messages; hiding documents recorded on microdot -- which can be as small as 1 millimeter in diameter -- on or inside legitimate-seeming correspondence; and even by using multiplayer gaming environments to share information.


While there are many different uses of steganography, including embedding sensitive information into file types, one of the most common techniques is to embed a text file into an image file. When this is done, anyone viewing the image file should not be able to see a difference between the original image file and the encrypted file; this is accomplished by storing the message with less significant bites in the data file. This process can be completed manually or with the use of a steganography tool.


Steganography is distinct from cryptography, but using both together can help improve the security of the protected information and prevent detection of the secret communication. If steganographically-hidden data is also encrypted, the data may still be safe from detection -- though the channel will no longer be safe from detection. There are advantages to using steganography combined with encryption over encryption-only communication.


The primary advantage of using steganography to hide data over encryption is that it helps obscure the fact that there is sensitive data hidden in the file or other content carrying the hidden text. Whereas an encrypted file, message or network packet payload is clearly marked and identifiable as such, using steganographic techniques helps to obscure the presence of the secure channel.


With the ceaseless usage of web and other online services, it has turned out that copying, sharing, and transmitting digital media over the Internet are amazingly simple. Since the text is one of the main available data sources and most widely used digital media on the Internet, the significant part of websites, books, articles, daily papers, and so on is just the plain text. Therefore, copyrights protection of plain texts is still a remaining issue that must be improved in order to provide proof of ownership and obtain the desired accuracy. During the last decade, digital watermarking and steganography techniques have been used as alternatives to prevent tampering, distortion, and media forgery and also to protect both copyright and authentication. This paper presents a comparative analysis of information hiding techniques, especially on those ones which are focused on modifying the structure and content of digital texts. Herein, various text watermarking and text steganography techniques characteristics are highlighted along with their applications. In addition, various types of attacks are described and their effects are analyzed in order to highlight the advantages and weaknesses of current techniques. Finally, some guidelines and directions are suggested for future works.


The main contributions of this paper are summarized as follows:(i)We present a brief overview of existing literature on text watermarking categories, architecture, applications, attacks, and evaluation criteria.(ii)We summarize some information hiding techniques which are focused on altering the structure and content of the cover text in order to hide secret information.(iii)We provide a comparative analysis of the summarized techniques and evaluate their efficiency based on the specified criteria.


Text watermarking techniques have various strategies and schemes which are dependent on the applications of the methods. In other words, the aim of watermarking determines whether the algorithm should be a fragile or robust tool; thus, it can be used to prove the integrity or originality of the text accordingly. Practically, developing a robust algorithm is not easy and requires considering the balance among multiple criteria that must be taken into account. Currently, there are a few text watermarking techniques which have been introduced; hence it is hard to find literature addressing its limitations. In this section, we introduce some related works which are focused on altering the structure and content of text in order to embed the hidden information [6, 7]. From the text processing point of view, text watermarking algorithms can be classified into one of the categories in Figure 4, namely, linguistic (natural language) and structural (format based).


To demonstrate the hiding process of above techniques, we implemented them on highlight examples (e.g., this process only embeds one bit in the cover text), which are depicted in Table 3. Moreover, the comparative analysis of the evaluated techniques in terms of criteria is summarized in Table 4.


Al-Nofaei et al. (2016) proposed a Kashida based steganography technique for Arabic digital texts. This method improves the feature of hiding data within the Kashida character in the Arabic text documents using whitespaces between words. In practice, this method provides high imperceptibility and better capacity compare to other techniques; however, its robustness is low against tampering and retyping attacks [50].


Por et al. (2012) introduced a data hiding method called UniSpaCh, which employs the Unicode special spaces in order to hide secret information into the Microsoft word files. The method utilizes specific locations such as interword, intersentence, end-of-line, and end of paragraph spaces to conceal a secret message [22]. In addition, a combination of double spaces is utilized for embedding the secret bits as depicted in Table 6.


To demonstrate the hiding process of structural techniques, we implemented them on highlight examples that are depicted in Table 12. Herein, the implementation means evaluation of selected techniques based on their embedding methods.


Assume that we aim to protect the documents in the dataset by hiding a watermark binary (60 bits) into their text contents. Therefore, we can analyze the efficiency of selected techniques in terms of criteria. Table 15 indicates the embedding capacity of evaluated techniques, which are calculated by using (1). Moreover, Figure 5 illustrates the embedding capacity of evaluated structural techniques.


Information hiding is a very powerful and flexible technique that can be employed in various ways to protect valuable information in different areas such as copyright protection, secure communication, and authentication. Although the efficiency of text hiding techniques has drawn attention much from academic researchers, it is still lacking a precise analysis modeling that can take the intrinsic criteria of the text hiding industry into account during the evaluating efficiency. As we already pointed out, there are four common criteria for efficiency analysis, which are dependent on the way of embedding. In other words, the embedding methods generally determine how to analyze the efficiency of the text hiding techniques.


Therefore, to evaluate the efficiency of a certain algorithm, it is required to be compared with previous works within the same category (e.g., linguistic or structural). In addition, we have outlined some various limitations of two major categories of text hiding techniques in Table 19, which provide a better understanding of the state-of-the-art and hopefully help in developing future works.


Practically, the linguistic techniques have more limitations compared to structural techniques. Due to extra dictionaries (WordNet) and high computational cost, moreover, a few researchers focused on linguistic based methods in recent years. Over the last two decades, many structural techniques have been introduced to improve the efficiency of text hiding techniques by considering the optimum trade-offs between criteria. However, the robustness of these techniques needs to be more improved against tampering attacks in terms of security requirements. In the following, we suggest some directions aimed at guiding cyber security researchers on the best options to utilize various types of text hiding techniques depending on the characteristics of the applications. However, we have to mention that these suggestions are general and empirically derived rules of thumb; these guidelines must not be considered rigidly or dogmatically.


(ix) To sum up, which kind of techniques provides more accuracy for copyright protection of text documents? We cannot give a precise and perfect answer to this question. The researchers must take into account many things like various merits and demerits of text hiding techniques, together with the guidelines that we have collected. In addition, they should ponder whether the text hiding techniques could be appropriate or not for their applications. When the researcher realizes that some of the merits of a specific technique can provide a valuable benefit to the specific needs of the application at issue; thus it should probably be given a try.


This case study provides a comparative analysis of existing information hiding techniques, especially on those ones that are focused on altering the structure and content of digital texts for copyright protection. We looked at a range of available approaches and attacks over the digital text documents in order to explain current security issues in the copyright protection industry. Moreover, we outlined two categories of text watermarking techniques based on how to process digital texts to embed the watermark bits, namely, linguistic (or natural language) and structural (format based). Linguistic techniques alter the text content and sometimes even the original meaning of sentences for embedding the watermark, which is not desirable and hence hard to apply. Using this kind of methods is not suitable to protect sensitive documents. The structural techniques utilize some characteristics of text such as layout features (e.g., interwords spaces and interline spaces), and format (e.g., text color, text font, and text height). Format based methods do not retain the watermark against reformatting, conversion, and even sometimes a simple copy of the text into another file. Those structural techniques utilize Unicode control characters for embedding (e.g., zero-width spaces and special spaces) the watermark bits into the original text and are able to protect the watermarked text against reformatting, tampering, and copy attacks to some extent. This kind of techniques can be applied to sensitive documents due to having shown a greater degree of imperceptibility and optimum robustness. Finally, we have suggested some of the guidelines and directions that could merit further attention in future works. 041b061a72


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