# A Comparative Analysis of Arabic Text Steganography
## 4 Arabic Text Steganography
### Unicode Method  
Unicode is an international character encoding format for displaying text for data processing. This standard is compatible with ISO/IEC 10646-1:2000 version 2. ISO/IEC 10646 has the same characters and codes. Unicode allows the encoding of all characters used in the world's writing systems. This standard employs 16-bit encoding, which allows for a total of 65,000 characters. This implies that it is possible to specify and define 65,000 characters in different modes such as numbers, letters, and symbols in various languages. Furthermore, due to the vast amount of space devoted to characters, this standard contains the majority of the symbols needed for high-quality typesetting. The languages whose writing systems can be supported by this standard are Latin (covering most of the European languages), Cyrillic (Russian and Serbian), Greek, Arabic (including Arabic, Persian, Urdu, Kurdish), Hebrew, Indian, Armenian, Assyrian, Chinese, Katakana, Hiragana (Japanese), and Hangeul (Korean). This standard also includes several mathematical and technical symbols, punctuation marks, arrows, and other marks. The Unicode standard consists of two groups of codes for the Arabic alphabets. The first is the representative code, and the second is the code of the letter's possible shapes. Separate characters are allocated for Persian letters with semantics or shapes that are significantly different from Arabic letters despite the unification of codes with common characters. This implies that separate places have been allocated to Persian special letters () and two other Persian letters () that are different from their corresponding Arabic letters in terms of appearance. The Unicode approach utilizes the various possible Unicode values of the same alphabet to conceal the bits. It is suitable for use on the public channel and modern devices such as smartphones. The authors of [97] proposed the usage of Unicode characters by inserting a normal space after pseudo-pace to embed \"1\" and no insertion to embed \"0.\" In that same year, the authors of [98] presented a design that utilizes \"La\" to hide the secret message. The word has two forms in Arabic writing: Normal form and special form. The Unicode of the normal form is used to conceal \"0,\" and the special form conceals \"1.\"  
Later, another Unicode technique was suggested where each Persian or Arabic letter has one unique code [99]. This code displays the letter in an isolated form and acts as a representative for the word. For each word in the text, it is possible to save a letter using the representative letter or the code of its correct shape (with respect to its position in the word). For hiding 0 bits in the word, the first option is used to save the word. Similarly, for hiding 1 bit, the second option is used. The authors of [100] applied the similarity between Arabic and Persian characters \(\approx\)\(\bigtriangleup\) and \(\approx\)\(\bigtriangleup\)\(\bigtriangleup\) to hide the bit \"0.\" The Arabic characters \(\ll\)\(\bigtriangleup\)\(\bigtriangleup\) and \(\ll\)\(\bigtriangleup\)\(\bigtriangleup\) were applied to hide bit \"1.\" One approach used the isolated letters in Arabic text with Run Length Encoding (RLE) to embed the secret bits [101], where the secret bit streams are converted to groups of 0s and 1s by applying RLE. The Unicode characters related to the isolated letters are changed to embed the secret bit \"1\" or unchanged to embed the secret bit \"0.\"  
Likewise, the isolated letters in Urdu text [102] changed the Unicode character to hide the secret bits. The secret message is encrypted as an encipher text by applying RSA. The enciphered text is converted to bitstream and divided into even blocks. Randomization and swapped functions are then applied to these blocks. The Unicode equivalents of the isolated letters are changed to cover bit \"1\" in each block or unchanged to cover \"0.\"  
Another Unicode system that involves a modified RLE was presented by the authors of [78].