Information hiding methods for Excel table formats

1 Overview information hiding technology as a technology to ensure information security, has been rapidly developed in recent years. Video, audio, image files because of the greater visual, the auditory redundancy is an important carrier of information hiding, so the information hiding technology based on video, audio and image is widely studied, but the corresponding covert analysis technology has been developed rapidly, which poses a great threat to the information hiding technology based on video, audio and image. , scholars began to study the hidden features of better algorithms and hidden vectors. In the paper [1-2], a text based information hiding technique is proposed, and a single text is used as the covert carrier. Literature [3] studies the information hiding technology based on PDF, and takes PDF file as covert carrier. In [4-5], the information hiding technology based on XML and Excel is presented respectively.

Excel table format is a public compressed table standard published by PKWare company, which is one of the most widely used format for file transfer in computer network, especially on Internet. By studying the standard format of Excel table, this paper presents a general information hiding method based on Excel table and an information hiding method based on Excel format in Excel2007. The experimental results show that the above method is effective and has good concealment.

2EXCEL table structure features and Analysis 2.1Excel table structure Excel tables are generally composed of 3 parts, compressed source file data area, compressed source file directory area and compressed source file directory end of the flag, where compressed source file data area main record compressed form internal source file file name, Compressed file size before and after the compressed file data and other information; The compressed source file directory area mainly records the compressed source file's attribute information, including the file name, the file compression before and after the size and the compressed file data in the entire compressed table's offset position and so on; Compressed source file directory End flag main record compressed source file directory area size, The total number of records in the directory and the location of the directory area at the offset of the entire Excel file [6]. Figure 1 is a table example. The structure description of Excel, contains A.txt, B.xml, c.jpg, d.doc4 source files, corresponding compressed source file data area and compressed source file directory area each have 4 records.

2.2EXCEL table Structure Analysis when you open a compressed form with compression decompression software (such as Winexcel, WinRAR, etc.), the software interface displays the source files inside the entire compressed form, and the source files (including the source files within the folder) are all derived from the records in the compressed source file directory area. When you open a source file, it is actually compressed source file directory area file record index found in the compressed source file data area of the corresponding source file data, after the solution to restore the original source table. Imagine if you add a source file to the compressed source data area, and you do not add the corresponding record in the file directory, if the Excel table opens normally, and if the added source file is displayed, you can find the answer by following the experiment.

in example. Excel table, clears the D.doc file in the compressed source file directory area record D.docindex, only retains its in the source file data area The record, and in the source file directory end sign In accordance with the Excel table format specification makes the corresponding modification, produces the new example. Excel table to see the new example in the structure as shown in Figure 2. Whether the Excel table opens normally, D.doc can be displayed. Experimental environment: Cpue44002ghz, Memory 2GB, operating system WindowsXPSP2, application software winexcel12.0pro,ultraedit-3212.20a. The following experimental data are measured in the above environment.

Experiments show that the new example. The Excel table works properly and does not display the D.doc table when opened with Winexcel, but when opened by UltraEdit-32, you can see D.doc records in the compressed source file data area (with 04034B50 as the start flag). Description D.doc The table is hidden in the new Example.excel table.

3 Information hiding and detecting methods based on Excel table structure 3.1 Hiding algorithm this article combines the Excel table structure above to design a way to hide information in an Excel table: a form m (can be in any format) that contains secret information Add to the Stealth Carrier C.excel table, delete the secret form m in the C.excel compressed source file directory area records, modify the compressed source file directory end of the corresponding information in the label, generate a new loaded C1.excel table. The hidden method, as shown in Figure 3, is detailed in algorithm 1.

Fig. 3 General form Concealment Algorithm 1 general form information hiding algorithm input the original carrier Excel file, the secret form output contains the dense Excel form Step1 adds the secret form to the original carrier table, produces the new Excel table.