# A Dynamic Multi-Layer Steganography Approach Based on Arabic Letters' Diacritics and Image Layers
## 2 Related Work
### Arabic Text Steganography Methods
However, the problem remains with the limited capacity for hiding the secret message. The authors of [38] lid information in Arabic texts using invisible letters, namely ZWNJ (zero width non-joiner) and ZWJ (zero width joiner). ZWNJ and ZWJ are used as connectors to concatenate other letters together. This steganography method has limited capacity, as it relies only on these two symbols. However, it is characterized by imperceptibility [39]. In [40], the authors proposed a steganography approach that causes no noticeable change in the original text using separate letters in Arabic. The authors of [41,42] extended [40] by encrypting the secret before hiding it. While encryption provides robust concealment, relying solely on two symbols in the encryption process limits the system's overall capacity. **Using Diacritics:** Several studies proposed diacritics-based steganography approaches. The authors of [43] used only the Fatah diacritic for concealment, as it is one of the most \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Isolated** & **At its End** & **In its Middle** & **At the Beginning of the word** \\ \hline \(\underline{\varepsilon}\) & \(\underline{\varepsilon}\) & \(\underline{\varepsilon}\) & \(\underline{\varepsilon}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Example of the character encoding method based on a letter’s position. Figure 6: Example for letter shapes and edges method. frequently used diacritics in Arabic text. A disadvantage of this approach is the small secret capacity, as it only uses one diacritic. [PERSON] et al. improved the previous approach by using more than one diacritic [38]; however, this approach lacks coherence and robustness. The researchers in [44; 45] took advantage of the fact that the diacritics in Arabic texts are not compulsory. Accordingly, they proposed hiding the diacritics or keeping them based on the secret. One of the advantages of this method is its high capacity, as the hidden diacritics themselves may contain some information. One of the weaknesses of this method is that the changes in diacritics' positions must be secure. Another approach was proposed based on stacking diacritics in the written text without obvious visual indicators [46]. Similarly, [47] proposed a steganography approach based on reversing the direction of diacritics, as in Figure 7. However, one of the limitations of the methods proposed in [46; 47] is their small capacity due to the number of diacritics and the ease of detection. In addition, [48] utilized the Fatah (\(\circ\)) and Kasrah (\(\circ\)) diacritics in the concealment process. This drawback is that the hiding places in the cover text are not random. After analyzing previous studies, we found that several methods were proposed to hide secrets in Arabic texts. Some of these methods involve changing the form of the diacritics or stretching the letters, while others involve replacing one diacritic with another. Some studies also used a combination of these methods. In addition, researchers have focused on specific criteria to test the effectiveness of their methods, such as the capacity of the steganography method, the imperceptibility of the hidden secrets, and the robustness of the methods. However, based on our literature review, embedding secrets in texts is considered one of the weakest steganography methods compared to embedding secrets in pictures and video files. This is because this method has limited secret capacity. To overcome this limitation, we propose a multi-layered system that uses a new method of concealing secrets in Arabic texts. This method is difficult to detect with the naked eye and uses a multi-layered approach to conceal medium-sized and large secrets.