A Review of Text Watermarking: Theory, Methods, and Applications <s> A. ROBUSTNESS <s> Digital watermarking is a nascent but promising technology that offers protection of unencrypted digital content. This paper is a brief technical survey of the multimedia watermarking landscape. The three main technical challenges faced by watermarking algorithms are fidelity, robustness and security. Current watermarking methods offer possibly acceptable fidelity and robustness against certain types of processing, such as data compression and noise addition, but are not sufficiently robust against geometric transforms such as scaling and cropping of images. Theoretical approaches have been developed that could lead to secure watermarking methods, but substantial gaps remain between theory and practice. <s> BIB001 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> A. ROBUSTNESS <s> In this paper we discuss natural language watermarking, which uses the structure of the sentence constituents in natural language text in order to insert a watermark. This approach is different from techniques, collectively referred to as "text watermarking," which embed information by modifying the appearance of text elements, such as lines, words, or characters. We provide a survey of the current state of the art in natural language watermarking and introduce terminology, techniques, and tools for text processing. We also examine the parallels and differences of the two watermarking domains and outline how techniques from the image watermarking domain may be applicable to the natural language watermarking domain. <s> BIB002 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> A. ROBUSTNESS <s> Synchronization is one of the most challenging elements of a watermarking system. In this paper, we survey and classify methods employed for watermark synchronization and highlight some inherent difficulties in synchronization that arise due to the nature of multimedia signals. We then propose a framework that addresses these hurdles in practical applications. Our framework utilizes feature-based embedding in concert with error correction codes capable of handling not only substitutions caused by various perturbations but also insertion and deletion events caused by erroneous feature estimates. We present a practical scheme for speech watermarking based on the framework. Experimental results show that the proposed methodology indeed enables synchronization in scenarios where a mismatch in estimated features between embedder and receiver would otherwise cause synchronization loss. We explore connections of the framework with recent theoretical analyses of watermark synchronization. <s> BIB003 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> A. ROBUSTNESS <s> At present, the research on content authentication of text documents has become the focused problem. In this paper, a novel semi-fragile text watermarking scheme is proposed for content authentication of Chinese text documents. In this method, the host document is divided into two text blocks by utilizing the thought of Chinese mathematical expression. Two watermarks generated by using the chaotic encrypting algorithm to encrypt the hashing value of the text document with two different keys respectively, are embedded into the two text blocks. These two different keys are generated by computing the frequency and stroke numbers of Chinese characters of two different text blocks. When the content of the watermarked text document is modified, the extracted results of two text blocks will not match, and the authentication result of the text document will be false. The experimental results indicate that the proposed scheme is secure and efficient. <s> BIB004 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> A. ROBUSTNESS <s> Security issues of text watermarking are greatly different from those of other multimedia watermarking, in terms of its specific requirements and characteristics of text watermarking. The security theory of text watermarking is proposed in this paper, and the following security topics are discussed: (i) the classification and application of text watermarking; (ii) the classification and analysis of attacks; (iii) the watermarking model and security countermeasures. Other open issues and further challenges related to text watermarking are also addressed. <s> BIB005 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> A. ROBUSTNESS <s> One of the most important techniques of information hiding is a steganography. Steganography is the art of hiding information within other information or carriers (i.e. text, image, video or audio) in such a way that it is hard or even impossible to tell that it is there. In This paper, a new text steganography method is proposed. The main goal of this method is to use text file as a carrier for the secret message data in such a manner that the resultant text file attracts no attention and hold the same meaning of the original file. <s> BIB006 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> A. ROBUSTNESS <s> The issue of protecting scientific and intellectual products and publications ownership constitutes an important deal within the domain of securing and protecting information. Digital watermarking is used to identify the ownership of the copyright and in authentication process. In this paper, an invisible blind watermarking method utilizing the word space in Arabic text is proposed. Since the pseudo-space is very small space used to separate two parts of the same word, it is inserted before normal space and after pointed letter to hold the binary bit 'one', and it is inserted before normal space and after un-pointed letter to hold binary bit 'zero'. The comparative results obtained by testing our proposed method with some of existing Arabic watermarking methods using four variable size text samples. The results show that our method has a higher capacity ratio and imperceptibility than other watermarking techniques. <s> BIB007
The robustness of a system can be defined as the ability and strength of the technique to resist any attack that aims at retrieving or modifying the hidden data BIB001 . The watermark data must be securely embedded and retrieved, so that they can survive any attack on the watermark. The watermark must withstand all attacks and must be retrievable for verification. Robustness constitutes an essential requirement in order to proof of ownership, copy control, identification, and fingerprinting where conceivable distortion is inevitable and there is a concern about the removal of the watermark. The most important feature of robustness is that even if a third party can detect the watermark, it cannot be destroyed without distorting or altering the cover file. System robustness can be divided into three categories: robust, fragile, and semi-fragile based on the level of modification done on the hidden data BIB004 , BIB003 . In the robust technique, the data are protected and hidden from unauthorized access and modification. On the other hand, a fragile data hiding system is not robust and cannot withstand an attack on the system, and a semi-fragile technique means that the hidden data can only resist some attacks. Thus, robustness can be used to measure and differentiate between good and bad text watermarking by assessing how many attacks it can resist. No exact means are available to measure the robustness. However, in the case of text watermarking, the attacks attempted on breaking the watermarked data can be used in order to measure the robustness. The two types of attack that are usually directed at watermarked data are formatting and content attacks BIB005 , BIB007 , BIB002 , BIB006 . Therefore, if a system is able to prevent those attacks, it is considered a robust system. If it can only prevent half or none of the attacks, it is considered a semi or non-robust system.