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L07-Ciphers-Substitution - Poly-Graphic Substitution...

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1 Poly Poly - - Graphic Substitution: Graphic Substitution: Playfair Playfair (1854) (1854) Encrypts pairs of letters in each step Build a 5 x 5 table of the letters using the key and other letters Example: Key = ”MONARCHY” M O N A R C H Y B D E F G I/J K L P Q S T U V W X Z
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2 Playfair Playfair Cipher Cipher Rules for substituting a pair of plaintext letters: Repeated letters in the plaintext are separated with a filler letter (such as X) Two plaintext letters that fall in the same row of the 5 x 5 table, are replaced by two letters that reside to their immediate right in the table (with circular wraparound) Two plaintext letters that fall in the same column of the 5 x 5 table, are replaced by two letters that reside their immediate beneath in the table (with circular wraparound) Otherwise, each plaintext letter (of a pair) is replaced by the letter that lies in its own row and the column occupied by the other plaintext letter (of the pair)
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