Method for embedment and extraction of PDF document hidden information according to composite font

A technique for hiding information and extracting methods, which is applied in the field of embedding and extracting hidden information in PDF documents based on composite fonts. It can solve problems such as damage to daily reading operations and saving operations, and difficult extraction of hidden information, and achieve good visual concealment and editing behavior. robust effect

Inactive Publication Date: 2014-01-29
SUN YAT SEN UNIV
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AI Technical Summary

Problems solved by technology

[0004] Existing information hiding technologies based on PDF documents are easily destroyed by various daily reading operations and saving operations of documents, and the embedded hidden information is difficult to be completely extracted

Method used

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  • Method for embedment and extraction of PDF document hidden information according to composite font
  • Method for embedment and extraction of PDF document hidden information according to composite font
  • Method for embedment and extraction of PDF document hidden information according to composite font

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Embodiment 1

[0050] Such as figure 1 As shown, it is a schematic diagram of the encoding process of composite fonts in PDF documents. The encoding of composite fonts is to map the character codes in TJ to Unicode codes, and then compile the Unicode codes into specific characters and display them on the document page. A large number of unused character codes are reserved in a specific PDF document, and the unused character codes are transparent to the PDF document, so the hidden information can be encoded using the character codes reserved in the PDF document, and then One or more text objects are constructed to be embedded in the content of the page display flow of the document without affecting the page display of the document. The present invention is to map hidden information into transparent character codes of compound fonts in equal parts, and then disguise the transparent character codes as one or more text objects and embed them in documents.

[0051] Such as figure 2 Shown is a ...

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Abstract

The invention relates to the field of multimedia information safety, in particular to a method for embedment and extraction of PDF document hidden information according to a composite font. The method for embedment comprises the steps that a data stream of a PDF document is read in; the composite font in the PDF document is searched for, the composite font appearing firstly serves as a target, transparent character codes in the composite font are found, and a transparent character code set is established; the hidden information is read and divided into sections, and the hidden information is mapped to elements in the transparent character code set in sections; one or more text objects are established through transparent character codes obtained through mapping; the text objects are written in an unzipped PDF page content stream; the content stream is zipped again and written in a file body ; according to the length of the content stream which is zipped again, a cross-reference list and an end of a file are updated, and a PDF document with the hidden information is formed. The method for embedment and extraction of the PDF document hidden information according to the composite font is robust with respect to ordinary edition behaviors of documents.

Description

technical field [0001] The present invention relates to the field of multimedia information security, more specifically, to a method for embedding and extracting hidden information of PDF documents based on compound fonts. Background technique [0002] In recent years, with the rapid development of network technology, people have begun to transmit and obtain information more and more through the Internet. At the same time, new office models such as e-commerce and e-government are being widely used, and more and more administrative and commercial documents, such as authorization letters, registration forms, contracts, invoices, etc., have begun to be circulated and transmitted in the form of electronic documents. However, in the open environment of the Internet, malicious acts such as copying and tampering always threaten the copyright ownership of electronic documents, and a large number of copyright theft, illegal transmission, information forgery and other problems emerge ...

Claims

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Application Information

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IPC IPC(8): G06F21/10G06F21/64
CPCG06F21/10G06F21/60G06F21/1062G06F21/1066
Inventor 刘红梅林少柳黄继武
Owner SUN YAT SEN UNIV
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