# E-SAWM: A Semantic Analysis-Based ODF Watermarking Algorithm for Edge Cloud Scenarios
## 2 Related Work
### Document Watermarking Techniques  
The file is a prominent data format used for data sharing. In the process of sharing files from the cloud (bank side) to the edge cloud (application side), it becomes crucial to monitor potential data leakage at each step. This concern is particularly relevant for the edge side, where the development of a watermarking algorithm that possesses high levels of transparency, concealment, robustness, and capacity has become a subject of significant academic interest. Electronic document formats can be categorized into two types: streaming documents and versioned documents. Streaming documents, such as Word and TXT files, support editing, and their display may vary depending on the operating system and reader version. On the other hand, versioned documents have a fixed layout that remains consistent across different operating systems and readers. OFD is an innovative electronic document format that conforms to the \"GB/T 33190-2016 Electronic Document Storage and Exchange Format--Layout Documents\" standard [13]. OFD was specifically developed to fulfill the demands of effectively managing and controlling layout documents while ensuring their long-term preservation. By offering a dependable and standardized format, OFD facilitates the maintenance of consistent layouts and supports the preservation of electronic documents. Our work primarily concentrates on the watermarking technology for OFD files, which serves as the prevalent file format utilized in the financial sector. The OFD file format adopts XML (Extensible Markup Language) to define document layout, employing a \"container + document\" structure to store and describe data. The content of a document is represented by multiple files contained within a zip package, as illustrated in Figure 3. A detailed analysis and explanation of the internal structure components of an OFD file are provided in Table 1.  
Figure 3: Structure of OFD. In the realm of layout document formats, OFD and PDF are widely utilized. Watermarking techniques for layout documents can be categorized into several methods:  
1. Syntax- or semantics-based approaches: leveraging natural language processing techniques to replace equivalent information, perform morphological conversions, and adjust statement structures to facilitate watermark embedding [6; 14];
2. Format-based approaches encompass techniques such as line shift coding, word shift coding, space coding, modification of character colors, and adjustment of glyph structures [15];
3. Document structure-based approaches leverage PDF structures like PageObject, imageObject, and cross-reference tables, enabling the embedding of watermarks while preserving the original explicit location [16]. The field of PDF watermarking has reached a relatively mature stage of development. However, watermarking algorithms that rely on syntax and format modifications may alter the original text content, which conflicts with the requirement of preserving the originality of digital products. Consequently, watermarking algorithms based on the document structure are commonly employed to add watermarks to PDF files. [PERSON] et al. [17] presented a novel method for watermarking PDF documents, which involves embedding watermarks based on the redundant identifier found at the end of the PDF cross-reference table. By leveraging this technique, the original text content and display of the PDF remain unaltered, thereby achieving complete transparency when viewed using PDF readers. [PERSON] et al. [18] added watermarks based on the PageObject structure within the PDF structure, which offers resistance against attacks such as adding or deleting text to manipulate the page content[PERSON] By utilizing these document structure-based watermarking techniques, PDF files can be effectively watermarked without compromising the original content and maintaining transparency and integrity in PDF readers.