1 Embedding Compression in Chaos- Based Cryptography 嵌入壓縮功能到混亂加密法 IEEE Transactions on Circuits and Systems—II: Express Briefs, VOL. 55, NO. 11, NOV Kwok-Wo Wong, Senior Member, IEEE, and Ching-Hung Yuen Adviser ：鄭錦楸, 郭文中 教授 Reporter ：林彥宏

2 Outline Introduction Proposed Approach Encryption Procedures Decryption Procedures Simulation Results Conclusions

3 Introduction(1/4) Entropy coding Arithmetic coding Huffman coding Baptista-type Chaotic cryptosystem One-Dimensional Logistic Map:

4 Introduction(3/4) trajectory

5 Introduction(2/4) S S-1 S-2 S % a b c $ Alphabet unit Sit numberSpacing position

6 Introduction(4/4)

7 Proposed Approach Number of Occurrence for Symbol Map Function Search Mode Mask Mode Huffman Tree Regenerate Chaotic Trajectory Extract Mask Bit Find Out Iteration Number Lookup Table Encryption Decryption Mask Intermediate Sequence

8 Proposed Approach (A,B,C,D)=(0.5, 0.25, 0.125, 0.125) phase space [0, 1] is divided into 256 partitions A=128 B=64 C=32 D=32

9 Proposed Approach more probable symbols are encrypted by searching in the dynamic lookup table less probable symbols are masked by a pseudorandom bitstream

10 Encryption Procedures Step1) Scan the whole plaintext sequence once Step2)

11 Encryption Procedures Step3) encrypt each plaintext symbol sequentially if the number of iterations required is smaller than a preselected maximum value, this symbol is considered as encrypted by the search mode; Otherwise, it will be encrypted by the mask mode eight masking bits are extracted from the least significant byte of the chaotic map output: Step4) after all the plaintext blocks have been processed, a Huffman tree is built for all the collected number of iterations, including zero if intermediate sequence exceeds the plaintext length, this means that no compression is achieved at all; encrypted by the all-mask mode

12 Encryption Procedures

13 Encryption Procedures Step5) binary mask sequence and the intermediate sequence are divided into 32-bit blocks

14 Decryption Procedures key and the plaintext specific information must be delivered to the receiver secretly secret key includes the parameters and the initial value of the chaotic map and also the initial cipher block information includes the name and length of the plaintext file, the encryption mode Step1) using the shared secret parameters and the initial conditions to regenerate the chaotic trajectory extract the mask bits if all-mask mode was used in encryption, the output sequence is already the plaintext; Otherwise, it is the intermediate sequence Step2) Scan the intermediate sequence sequentially find out the number of iterations required nonzero number of iterations and determine the final partition visited by the chaotic trajectory

15 Simulation Results Compression Ratio Encryption and Decryption Speed Key Space and Sensitivity Plaintext Sensitivity

16 Compression Ratio

17 Compression Ratio the compression performance of the second configuration is better for most of the files scheme is not compression-oriented, but is built on a chaotic cryptosystem

18 Encryption and Decryption Speed encryption speed ranges from 684kB/s to 4.81MB/s decryption speed varies from 955 kB/s to 2.37MB/s

19 Key Space and Sensitivity Key Space encryptions using all-mask mode were performed with a small change in only one of the parameters the ciphertext is very sensitive to the key

20 Plaintext Sensitivity The results are 50.00% (bit change at the beginning of plaintext), 50.04% (middle), and 50.01% (end), respectively. They are all close to 50%, which imply that the ciphertext is very sensitive to the plaintext.

21 Conclusions The key space of the proposed cryptosystem is equivalent to 130 bits Simulation results show that all the standard test files are compressed to a satisfactory degree, and the ciphertext is very sensitive to a tiny change in the key or the plaintext the compression capability is achieved while the security is maintained scheme also guarantees that the ciphertext is not longer than the plaintext