Hindawi Security and Communication Networks Volume 2018, Article ID 5325040, 22 pages https://doi.org/10.1155/2018/5325040 Review Article A Comparative Analysis of Information Hiding Techniques for Copyright Protection of Text Documents Milad Taleby Ahvanooey ,1 Qianmu Li ,1 Hiuk Jae Shim,2 and Yanyan Huang3 1 School of Computer Science and Engineering, Nanjing University of Science and Technology, Nanjing, China 2School of Computer and Sofware, Nanjing University of Information Science and Technology, Nanjing, China 3School of Automation, Nanjing University of Science and Technology, Nanjing, China Correspondence should be addressed to Milad Taleby Ahvanooey; [email protected] and Qianmu Li; [email protected] Received 6 October 2017; Revised 28 December 2017; Accepted 16 January 2018; Published 17 April 2018 Academic Editor: Pino Caballero-Gil Copyright © 2018 Milad Taleby Ahvanooey et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 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 signifcant part of websites, books, articles, daily papers, and so on is just the plain text. Terefore, 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. Tis 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 efects are analyzed in order to highlight the advantages and weaknesses of current techniques. Finally, some guidelines and directions are suggested for future works. 1. Introduction Digital text watermarking is a data hiding technique which conceals a signature or copyright information called Following the progressive growth of Internet and advance- watermark inside a cover text in an imperceptible way. ment of online services, digital publishing has become an Separating the hidden watermark from the cover text is very essential topic and in the next-generation organizations, difcult due to the fact that watermarked text is invisible for ofces (e.g., institutions and publishers) seem to be paperless. everyone except the original owner. Recently, text watermark- Nowadays, various studies are in process to execute and ing has not drawn much attention from cyber security experts organize some ideas such as e-commerce, e-government, and and researchers. Tere are some reasons for that: the much online libraries. Digital publishing has many privileges, but lower capacity of text to retain data might be one of the main it has some fundamental threats such as illegal use of copy- reasons (i.e., compared to other digital media such as image, righted documents, manipulating the data, and redistributing audio, and videos). However, there are a number of reasons such information [1–3]. In this case, some protective solutions why we should pay more attention to it. Firstly, the text is consisting of copyright protection, integrality, authenticity, still a major form of universally applicable digital media. In and confdentiality are essential to prevent forgery and pla- other words, text is an important part of communication giarism problems. Downloading and manipulating a copy- between people compared to other media. Secondly, text righted text and thus reusing it without any control are easy watermarking has no clear evaluation criteria to analyze its these days; hence, copyright management is very necessary to efciency [6–10]. protect such information against modifying and reproducing Te diferent categories of information security systems processes [4–6]. are depicted in Figure 1. Te cryptography and information 2 Security and Communication Networks Information security systems Cryptography Information hiding Black-box cryptography Steganography Watermarking Gray-box cryptography Linguistic Technical White-box cryptography Working domain Type of documents Special Frequency Text Image Video Audio Structural Linguistic Figure 1: Diferent categories of information security systems. hiding are security systems that are used to protect data from Te main contributions of this paper are summarized as deceivers, crackers, hackers, and spies. Commonly, most of follows: the malicious users want to leave traces from cuts, manip- ulations, and infections [7]. Te cryptography scrambles a (i) We present a brief overview of existing literature on plain text into ciphertext which is reversible without data text watermarking categories, architecture, applica- loss. Te goal of cryptography is to prevent unauthorized tions, attacks, and evaluation criteria. access to the secret information by scrambling the content (ii) We summarize some information hiding techniques of information. On the other hand, information hiding is a which are focused on altering the structure and powerful security technique which hides a secret data in a content of the cover text in order to hide secret cover media (e.g., text, image, audio, or video) so that the information. trace of embedding hidden data is completely unnoticeable. (iii) We provide a comparative analysis of the summarized Te cryptography and information hiding are similar in a techniques and evaluate their efciency based on the way that both are utilized to protect sensitive information. specifed criteria. However, the imperceptibility is the diference between both techniques; that is, information hiding concerns how to Te rest of the paper is organized as follows. In Section 2, hide information unnoticeably. Generally, the information we review text watermarking literature and related studies. hidingcanbefurthercategorizedintosteganographyand In Section 3, we introduce individual text watermarking watermarking. Te aim of steganography is to hide a secret methods and analyze them based on evaluation criteria, and message in a cover media in order to transmit the secret we give some suggestions for the future works in Section 4. information; therefore, the main concern is how to conceal Finally, Section 5 draws the conclusions. the secret information without raising suspicion; that is, steganography needs to conceal the fact that the message 2. Literature Review is hidden. Watermarking is concerned with hiding a small data in digital fles such that the hidden data is robust to In what follows, we describe the existing literature on text alterations and adjustments. In other words, watermarking watermarking including architecture, the Unicode standard, aimstoprotectintellectualpropertyofdigitalmediaagainst text watermarking categories, applications, evaluation crite- unauthorized copy or access by embedding a watermark ria, and attacks. (visible or invisible) in the cove media which can remain beside the data, and it can be used whenever there is any query 2.1. Text Watermarking Architecture. AsshowninFigure2, about the originality of media (e.g., the hidden watermark digital text watermarking includes two main phases, namely, refers to the original owner) [2–10]. watermark embedding and watermark extraction. Over the last two decades, many information hiding tech- niques have been proposed in terms of text watermarking and (i) Watermark Embedding. Te embedding phase of text text steganography for copyright protection [11–14], proof of watermarking algorithm includes three stages. Te frst stage ownership [15–23], and copy control and authentication [24– is generating a watermark string which includes the owner’s 31]. Although the aim of steganography is diferent, it also name or other pieces of information (e.g., author and pub- can be used for the copyright protection of digital texts like lisher). In the second stage, the watermark string is converted watermarking. to a binary string, which is modifed by a hash function Security and Communication Networks 3 Key Digital watermark Digital watermark Key Embedding Extraction Te watermarked text is sharing (i) Watermark generation on the communication channel (i) Watermark extraction, (ii) Watermark securing Rehash, and detection (iii) Watermark inserting Attacks (ii) Watermark authentication (i) Alterations (ii) Distortions Original or cover text document (iii) Redistributions Watermarking No Tampered authenticator text document Yes Authenticated text document Figure 2: Digital text watermarking (embedding and extraction) architecture. according to an optional key, and then an invisible watermark and classical letters in many languages. Tis standard is string is generated for embedding it into special locations compatible with the latest version of ISO/IEC 10646-1:2017 in the cover text. Finally, it is inserted into special locations and has the same characters and codes of ISO/IEC 10646. where the watermark string will not be afected by attacks As of