1. Introduction to CLOCK_CONTROLLED STREAM CIPHER SYSTEM Sayed Mahdi Mohammad Hasanzadeh Hasanzadeh@Raymandcrypto.ir Zaeim Electronics industries 1380

2. Contents: Introduction to Clock_Controlled Stream Cipher Systems Former important attacks Conclusion

3. Introduction to Clock_Controlled stream cipher systems In A5 algorithm used from clock-controlled LFSR a tool for stream cipher designingLFSR Introduction Clock_controlled systemIntroduction A simple Clock_controlled systemsimple Types of Clock_controlled systemsTypes A statistical Model for any Clock_controlled systemstatistical Model

4. LFSR is used in stream cipher systems High period (2^L-1) Satisfied Golomb criteria Easy for implementation Low complexity

5. Introduction Clock_controlled system

6. A simple Clock_controlled system CR SR

7. types of Clock_controlled system Stop/go clock_controlledStop/go Step1/step2 clock_controlledStep1/step2 Step[D,K] clock_controlledStep[D,K] Cascade clock_controlledCascade –Cycle cascade clock_controlledCycle cascade –M-sequence clock_controlled –Multibit clock_controlled

8. Cascade clock_controlled

9. Statistical Model for any Clock_controlled system

10. Former important attacks Exhaustive searchExhaustive Divided and conquer attackDivided and conquer Correlation attackCorrelation Analyzing previous worksAnalyzing

11. Exhaustive search

12. Divided and conquer attack Each stage is independent with another stage Analyzing each stage with an arbitrary attack only –Correlation attack with : levenshtein distance novel distance

13. Correlation attack In this attack we search all initial states to find which state generates minimum distance. Levenshtein DistanceLevenshtein Novel Distance

14. Levenshtein Distance Levenshtein distance for non equal–length sequence comparison One sequence is obtained from the other by symbol substitution, deletion, and insertion The levenshtein distance defined as the minimum edit operations required to transform one sequence into the other.

15. Clock_controlled

16. Cycle cascade clock_controlled

17. Analyzing previous works Complexity in exhaustive search increases exponential with LFSR length In Divided & conquer attack: Are stages independed really? We don’t use dependence between output bits.

18. Conclusions Introduced Clock-Controlled Stream Cipher This type of stream cipher has good properties Introduced Former important attacks –Complexity in exhaustive search increases exponential with LFSR length –In Divided & conquer attack: Are stages independed really? We don’t use dependence between output bits. This type of stream cipher has weakness For using of this type of stream cipher should be careful and combine it with other elements