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A Fast Method for the Cryptanalysis of Substitution Ciphers
 Cryptologia
, 1995
"... It is possible to cryptanalyze simple substitution ciphers (both monoand polyalphabetic) by using a fast algorithm based on a process where an initial key guess is refined through a number of iterations. In each step the plaintext corresponding to the current key is evaluated and the result used as ..."
Abstract

Cited by 17 (1 self)
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It is possible to cryptanalyze simple substitution ciphers (both monoand polyalphabetic) by using a fast algorithm based on a process where an initial key guess is refined through a number of iterations. In each step the plaintext corresponding to the current key is evaluated and the result used as a measure of how close we are in having discovered the correct key. It turns out that only knowledge of the digram distribution of the ciphertext and the expected digram distribution of the plaintext is necessary to solve the cipher. The algorithm needs to compute the distribution matrix only once and subsequent plaintext evaluation is done by manipulating this matrix only, and not by decrypting the ciphertext and reparsing the resulting plaintext in every iteration. The paper explains the algorithm and it shows some of the results obtained with an implementation in Pascal. A generalized version of the algorithm can be used for attacking other simple ciphers as well. Keywords: Cryptanalysis,...
Sullivan and Weierud Breaking German Army Ciphers BREAKING GERMAN ARMY CIPHERS
"... 1945, have survived the end of the Second World War to the present day. Most of these messages are enciphered on the threewheel, steckered Wehrmacht Enigma. We present an account of a ciphertextonly cryptanalysis of these messages and give details of the Enigma procedures used in the networks. ..."
Abstract
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1945, have survived the end of the Second World War to the present day. Most of these messages are enciphered on the threewheel, steckered Wehrmacht Enigma. We present an account of a ciphertextonly cryptanalysis of these messages and give details of the Enigma procedures used in the networks.