Embedding and detecting watermarks

Abstract

A watermark embedding method for embedding a secret message sequence in a document. The techniques include obtaining layout information of the document, extracting a digest of the document by using a Hash function, calculating embedded positions where the secret message sequence is embedded in the document, and dispersedly hiding the secret message sequence in each of the calculated embedded positions by altering the layout of the document. Also provided is a watermark embedding apparatus, a corresponding watermark detecting method and apparatus, and a method and system for detecting document integrity. The integrity of documents in various forms can be detected, and secret information to be hidden can be embedded therein and extracted therefrom. The techniques described are not limited to the document either in soft copy or in hard copy and have good robustness.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority under 35 U.S.C. §119 to China Patent Application No. 200510084619.6 filed Jul. 14, 2005, the entire text of which is specifically incorporated by reference herein. BACKGROUND OF THE INVENTION [0002] The present invention generally relates to information security fields, and particularly to information security fields utilizing digital watermarking techniques and information hiding techniques. [0003] Paperless office environment and electronic transactions are extensively adopted in current business world. Many important documents, such as wills, forms, identification and contracts, etc., require strict authentication and integrity assurance. For those documents containing sensitive information, even a small revision, such as adding, deleting, or modifying a paragraph, phrase, or word, is not allowed since it may cause great change to the meaning of the content and lead to great damage in business activit...

AI Technical Summary

Benefits of technology

[0005] However, in most real applications, paper is still in an indispensable position. Signed documents are often printed out or faxed. In such cases, since digital signature requires side information (encrypted digest) transmitted together with the electronic document itself, it has noting to do with the case where electronic documents are printed out. Furthermore, digital signature can only ensure the integrity of the document, but cannot hide any additional information that the author will not let others to directly see.

[0010] Thus, an exemplary aspect of the present invention is a watermark embedding method for embedding a secret message sequence in a document. The method includes an obtaining operation of obtaining layout information of the document. An extracting operation is performed to extract a digest of said document by using a Hash function. A calculating operation calculates embedded positions where the secret message sequence is embedded in the document. A hiding operation dispersedly hides the secret message sequence in each of the calculated embedded positions by altering the layout of the document.

[0009] Existing watermarking techniques are mostly symmetric watermarking techniques. In general, the integrity protection by means of symmetric watermarking techniques is realized by firstly encrypting the signature by applying public key algorithms into the digest of the text, and then hiding the encrypted digest into the document by symmetric watermarking techniques. However, for some applications, in addition to the need of verifying the integrity, there exists the need of adding extra secret information, for example, information which the author might not want others to see. If such information is embedded by means of symmetric watermarking, then a person, which is authorized to detect a watermark, can easily forge another watermark without permission, since embedding and extracting of the symmetric watermark can be derived from each other.

Problems solved by technology

For those documents containing sensitive information, even a small revision, such as adding, deleting, or modifying a paragraph, phrase, or word, is not allowed since it may cause great change to the meaning of the content and lead to great damage in business activities.

Furthermore, digital signature can only ensure the integrity of the document, but cannot hide any additional information that the author will not let others to directly see.

Such embedded watermark may be a segment of characters, identification or serial numbers and the like, and is often invisible or unobservable.

Since text watermarking is vulnerable to deliberate destroy, it may encounter big technical challenges when using it for content protection.

But in the application of integrity check, the potential attack is not to remove the watermark, but to modify the meaning of the watermark or the content.

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