Machine reconstruction of the Playfair cipher
نویسنده
چکیده
A Playfair cipher is a digraph substitution, where each letter pair of the plaintext is replaced by a letter pair in the ciphertext. The chart of substitutions is summarized by the placement of letters in a table, called the Playfair square, constructed in some customary manner from a keyword. We denote a substitution of plaintext digraph cd with ciphertext digraph ab by ab− cd. There are two rules to the substitution, depending on whether cd lie in the same row or column, or if they are simultaneously in different rows and columns. The cases are illustrated:
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