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Class-5-12-RC-10

Class-5-12-RC-10 - Random Cryptographic Systems Random...

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Unformatted text preview: Random Cryptographic Systems Random Cryptographic Systems ASSUMPTIONS ABOUT CRYPTOGRAPHIC TRANSACTIONS and we also have Example Plaintext space Octopus Cod Oyster Tuna Ciphertext space us Analysis of the “ciphertext only” Attack Theorem 1 H(K| C) = H(K) + H(M) - H(C) Proof The key is independent of the message Thus H(K,C) = H(K,M) H(K,C) = H(K) + H(M) Recall that Thus H(C) + H(K| C) = H(K) + H(M) Q.E.D. C = E (M) Analysis of the “known plaintext ” Attack Theorem 2 H(K| C,M ) = H(K) - H(C|M ) Proof C = E K(M) H(K,C,M) = H(C,M) + H(K| C,M ) H(K,M) = H(C,M) + H(K| C,M ) H(C,M) + H(K| C,M ) = H(K) + H(M) H(K,C, M) = H(K,M) H(K,M) = H(K) + H(M) H(C,M) = H(M) + H(C| M) gives H(M) + H(C| M) + H(K| C,M ) = H(K) + H(M) Q.E.D. ...
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