L06-Cipher-Substitution

L06-Cipher-Substitution - • Answer: The number of...

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1 Poly Poly - - Alphabetic Alphabetic • A table of 26 rows and 26 columns is built. Each row contains the 26 letters of the alphabet. • A keyword is used to select which of the mono- alphabetic ciphers to use. • Use a collection of related Mono-Alphabetic Ciphers Vigenere Vigenere Cipher (1553 Cipher (1553 …)
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2 Vigenere Vigenere Cipher Cipher - - Example Example • Example: Table with 6 letters (A, B, C, D, E, F): •K e y w o r d = B A D •P l a i n t e x t = c a b d e f •C i p h e r t e x t = D A E E E C plaintext key
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3 Strength of Strength of Vigenere Vigenere Cipher Cipher The strength of Vigenere Cipher is based on the fact that there are multiple ciphertext letters to which each plaintext letter can be mapped How many possible ciphertext letters can a single plaintext letter be mapped?
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Unformatted text preview: • Answer: The number of different letters of which the keyword is constructed 4 Attacks on Attacks on Vigenere Vigenere Cipher Cipher • Determine the length of the keyword – Detect identical sequences of ciphertext letters – If two identical sequences of plaintext letters occur at a distance that is an integer multiple of the keyword length, then the two corresponding sequences of ciphertext letters will be identical – Conjecture that the keyword length is the greatest common divisor of distances between identical sequences of ciphertext 5 Recommended Readings Recommended Readings • Trappe : Chapter 2 • Stallings : Chapter 2...
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This note was uploaded on 09/15/2010 for the course CSE IT325 taught by Professor Maniklaldas during the Fall '09 term at Punjab Engineering College.

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L06-Cipher-Substitution - • Answer: The number of...

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