introduction to clock_controlled stream cipher system sayed mahdi mohammad hasanzadeh...
TRANSCRIPT
Introduction to CLOCK_CONTROLLED STREAM
CIPHER SYSTEM
Sayed Mahdi Mohammad Hasanzadeh
Zaeim Electronics industries
1380
Contents:
• Introduction to Clock_Controlled Stream Cipher Systems
• Former important attacks
• Conclusion
Introduction to Clock_Controlled stream cipher systems
• In A5 algorithm used from clock-controlled
• LFSR a tool for stream cipher designing
• Introduction Clock_controlled system
• A simple Clock_controlled system
• Types of Clock_controlled systems
• A statistical Model for any Clock_controlled system
LFSR is used in stream cipher systems
• High period (2^L-1)• Satisfied Golomb criteria • Easy for implementation • Low complexity
Introduction Clock_controlled system
A simple Clock_controlled system
CR
SR
types of Clock_controlled system
• Stop/go clock_controlled
• Step1/step2 clock_controlled
• Step[D,K] clock_controlled
• Cascade clock_controlled– Cycle cascade clock_controlled– M-sequence clock_controlled– Multibit clock_controlled
Cascade clock_controlled
Statistical Model for any Clock_controlled system
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Former important attacks
• Exhaustive search
• Divided and conquer attack
• Correlation attack
• Analyzing previous works
Exhaustive search
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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
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Correlation attack
In this attack we search all initial states to find which state generates minimum distance .
• Levenshtein Distance• Novel Distance
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.
Clock_controlled
Cycle cascade clock_controlled
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.
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