07 - Introduction Stream Ciphers Cryptography and Protocols...

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Unformatted text preview: Introduction Stream Ciphers Cryptography and Protocols Andrei Bulatov Cryptography and Protocols Stream Ciphers 7-2 Pseudorandom Generators Let T(n), (n) be functions. A collection of random variables with is called (T, )-pseudorandom if A collection of functions is called a (T, )-pseudorandom generator if is (T, )-pseudorandom m(n) n > 0 the stretch of a PRG A PRG should be (T, )-pseudorandom for some superpolynomial pair (T, ) must be efficiently computable RC4 and Blum-Blum-Shub } { n X n n X } 1 , { } { } { , n T n U X ) ( } 1 , { } 1 , { : n m n n g )} ( { n n U g n g Cryptography and Protocols Stream Ciphers 7-3 Stream Ciphers Let be a pseudorandom generator producing, given a seed of length n, bit strings of length m(n) Let (K,E,D) be a SES defined as follows: K draws keys uniformly at random E to encrypt a plaintext P of length m(n) it applies to the key k and computes D same as E } { n g n g i i n i P k g C = )) ( ( Cryptography and Protocols Stream Ciphers 7-4 Security of Stream Ciphers Theorem ....
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07 - Introduction Stream Ciphers Cryptography and Protocols...

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