A Review of Text Watermarking: Theory, Methods, and Applications <s> D. SECURITY <s> This paper proposes a theory of watermarking security based on a cryptanalysis point of view. The main idea is that information about the secret key leaks from the observations, for instance, watermarked pieces of content, available to the opponent. Tools from information theory (Shannon's mutual information and Fisher's information matrix) can measure this leakage of information. The security level is then defined as the number of observations the attacker needs to successfully estimate the secret key. This theory is applied to two common watermarking methods: the substitutive scheme and the spread spectrum-based techniques. Their security levels are calculated against three kinds of attack. The experimental work illustrates how Blind Source Separation (especially Independent Component Analysis) algorithms help the opponent exploiting this information leakage to disclose the secret carriers in the spread spectrum case. Simulations assess the security levels derived in the theoretical part of the paper. <s> BIB001 </s> A Review of Text Watermarking: Theory, Methods, and Applications <s> D. SECURITY <s> Nowadays, the success of internet technology, made our life very much easy and convenient. But the major problem is to secure the data from duplication and unauthorized use. So the digital watermarking is used. With this technology, we embed the secret information into the actual information for protecting it from unauthorized use. By using this technique only authorized user can access the data. It may be classified into two domains that are spatial domain and frequency domain. In this paper, we have briefly discussed about these technologies and their pros and cons. <s> BIB002
Security refers to the ability of the system to prevent any unauthorized manipulation of the watermark BIB002 . The digital text should be secure enough to prevent any unauthorized removal of the hidden data and should be only modifiable by the owner  . Any potential attacker must not be able to modify or fabricate the hidden data without knowing the key BIB001 . Blind algorithms are useful in this respect as they ensure the security of the approach where the original cover data are not needed when validating the copyright owner of text. The unauthorized manipulation of the content of digital media can be prevented by upgrading the system efficiency and restricting access to authorized persons. In this case, it is important to ensure that the key is well hidden from any potential attacker. This can be done by securing it with cryptographic security. The system security can be enhanced by using a cryptographic application and digital signature, for which the data will be hashed using hash function. In order to evaluate the security of a system, it has to be assumed that the attacker knows the approach used for the watermark embedding. However, the key remains hidden under the cryptography protocol to ensure its security. In this case, the attacker will try to analyze the watermarked data and destroy the watermark. He or she should not be able to tamper with the watermark data without also changing the content of the data. In such a case, the watermark is considered as well secured. It is important to identify the best security protocol and policy in order to improve the text watermarking effectiveness. The application of the hash function and cryptographic algorithm must be taken into consideration when building the watermarking system.