Lecture4

Lecture4 - Lecture 4 More on Stream Ciphers CNT 5412...

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1 Lecture 4 More on Stream Ciphers CNT 5412 Network Security
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2 Binary One-Time Pad K[0] K[1] K[2] K[n-2] K[n-1] M[0] M[1] M[2] M[n-2] M[n-1] C[0] C[1] C[2] C[n-2] C[n-1] K[0] K[1] K[2] K[n-2] K[n-1] M[0] M[1] M[2] M[n-2] M[n-1]
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3 Idea behind stream ciphers (approximate a one-time pad) • Start with a fixed-length, shared secret. This is generally called the seed s. • Use a procedure that, with the seed as input, generates a stream of bits that seems random, but which is in fact deterministically computable (from s ). • Use this stream ( keystream ) as the one-time pad: XOR it with the plaintext. • Note: we previously showed how block ciphers could be used to generate stream ciphers
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4 Types of Stream Ciphers • A stream cipher is a finite state machine (finite input, fixed memory size, deterministic). Two main types: Key-auto-Key (KAK, synchronous) -- state determined by last bits of keystream Ciphertext-auto-key (CTAK, self- synchronizing) -- state determined by last bits of ciphertext
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This note was uploaded on 02/20/2012 for the course CNT 5412 taught by Professor Sudhir during the Spring '12 term at FSU.

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Lecture4 - Lecture 4 More on Stream Ciphers CNT 5412...

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