Midterm1-solution-key

Midterm1-solution-key - CSE 565 Computer Security Solution...

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1 CSE 565 Computer Security Solution Key for Midterm 1 Question 1: (4 + 6 + 5 points) a) A simple frequency analysis will determine the difference. If a monoalphabetic substitution is used, then the statistical properties of the ciphertext should be the same as that of language of the plaintext. A flat distribution will indicate that it is polyalphabetic cipher such as the Vigenere cipher. b) If the length of the keyword is guessed, then cryptanalysis becomes easier. If two identical sequences of plaintext letters occur at a distance that is an integer multiple of the keyword length, they will generate identical ciphertext sequences. The repeated sequences in the ciphertext can be easily identified. c) A perfect cipher is one that would use many alphabets for an unrecognizable distribution and no apparent pattern for the choice of an alphabet at a particular point. Examples are one-time pad and Vernam Cipher. They cannot be realized in practice due to problems such as need for an unlimited number of keys, requirement of truly
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This note was uploaded on 10/12/2010 for the course CSE 565 taught by Professor Shambhu during the Fall '09 term at SUNY Buffalo.

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Midterm1-solution-key - CSE 565 Computer Security Solution...

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