1. A Data Hiding Method for Text Documents Using Multiple-Base Encoding
Chair Professor Chin-Chen Chang
National Tsing Hua University National Chung Cheng University Feng Chia University

2. Outline Introduction Related works Proposed scheme
- Synonym substitution
- Text Steganography in Chat
- Emoticon-based Text Steganography in Chat
Related works
- Inter-word spacing scheme
- Chen et al.’s data hiding method
- The multiple-based notational system
Proposed scheme
Experimental results
Conclusions

3. Introduction Secrets ‧Data hiding with documents
‧Quality, capacity and security
Sender
Internet
Secrets
Receiver

4. Synonym substitution 0 wonderful 1 decent 2 fine Taichung is a 0 city
3 great
4 nice
Taichung is a
0 city
1 town
little
Secret message: (3)5(1)2
Taichung is a great little town

5. Text Steganography in Chat
Shirali-Shahreza, M.H., Shirali-Shahreza, M., “Text Steganography in Chat,” Proceedings of the Third IEEE/IFIP International Conference in Central Asia on Internet the Next Generation of Mobile, Wireless and Optical Communications Networks, Tashkent, Uzbekistan, Sep. 2007, pp. 1-5.

6. Text Steganography in Chat
SMS-Texting

7. Text Steganography in Chat
Usual abbreviated words
univ.  university
PC  Personal Computer
M.S.  master of science
UN  United Nations
Dr  doctor

8. Text Steganography in Chat
SMS list + abbreviated words list
 Check list
0  full form, 1  abbreviated form

9. Text Steganography in Chat
Embedding :
“Please call me when you feel upset.”
secret “10”
“Please CM when you feel upset.”
Extracting :
Check list
secret bits “10”

10. Emoticon-based Text Steganography
Emoticon-based Text Steganography in Chat

11. Emoticon-based Text Steganography
Phase1: Classify the emoticons by their meaning

12. Emoticon-based Text Steganography
Example: N = 16
hide log2N = 4 bits per emoticon
sender uses second symbol
receiver can extract 4 bits “0001”

13. Emoticon-based Text Steganography
Phase2: emoticon || sentence : secret = 0
sentence || emoticon : secret = 1
I lost my bag
secret = 0
I lost my bag
secret = 1

14. Emoticon-based Text Steganography
Phase3: emoticon , sentence : secret = 0
emoticon , sentence : secret = 1
, I lost my bag
secret = 0
I lost my bag
secret = 1

15. Emoticon-based Text Steganography
Zhihui wants to send secret bits “ ” to Alan3c.
Alan3c says :
You are a bad student!
Zhihui says:
1110
Alan3c says:
Just a kidding, you are the nicest guy I know in the world.
Zhihui says:
Phase1
Phase3
Phase2
001||1||1

16. Bender et al.’s Inter-word spacing scheme
This scheme exploits inter-word space of text to encode data.
Thisisabook.
Secret bits: { }
Thisisabook.

17. Chen et al.’s data hiding method
Keep spaces between groups unchanged.
Weemploythecombinationoftherepeatedwords…
Secret bits: { }
Space change: ＋ －　　　　　 ＋
We employthecombinationof therepeated words…

18. The multiple-based notational system
x = (48)10 = ( )
( ) = (48)10
1x5x3x2 + 3x3x2 + 0x2 +0 = 48
48 mod 2 = 0
(48-0)/2 = 24
24 mod 3 = 0
(24-0)/3 = 8
8 mod 5 = 3
(8-3)/5 = 1
1 mod 3 = 1

19. Proposed Scheme (1/2) The embedding phase
Secret: (106)10 = (???)645
Secret: (106)10 = (511)645

20. Proposed Scheme (1/2) The embedding phase
Secret: (??)10 = (511)645
Secret: (106)10 = (511)645

21. Experimental results

22. Conclusions
Provides a fast text hiding scheme that can achieve invisible security with computational efficiency.

23. Thanks for your listening