L15-Stream Ciphers - Stream Ciphers • Bit-wise or...

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Stream Ciphers Stream Ciphers • Bit-wise or Byte-wise encryption/decryption • Higher speed and lower hardware complexity • Synchronous stream ciphers – The keystream is generated independently of the plaintext or the ciphertext. – Using Pseudo-Random Number Generator Example : Linear Feedback Shift Registers • Self-synchronous stream ciphers – The keystream is generated from N previous ciphertext . Example : AutoKey
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Stream Ciphers Stream Ciphers Keystream Keystream Generator Generator
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Linear Feedback Shift Registers Linear Feedback Shift Registers • LFSRs are used in many applications • Many systems combine several LFSRs to increase the complexity and to reduce the correlation of bits attack • LFSR is fast in hardware and slow in software
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Linear Feedback Shift Register Linear Feedback Shift Register • Generation of pseudo random bits • Dependency on initial value • Length of cycle depends on function f and on length n
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Linear Feedback Shift Registers Linear Feedback Shift Registers
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L15-Stream Ciphers - Stream Ciphers • Bit-wise or...

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