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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 ..."
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Cited by 16 (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,...
The Applications of Genetic Algorithms in Cryptanalysis
, 1996
"... This thesis describes a method of deciphering messages encrypted with rotor machines utilising a Genetic Algorithm to search the keyspace. A fitness measure based on the phi test for non randomness of text is described and the results show that an unknown three rotor machine can generally be cryptan ..."
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Cited by 3 (0 self)
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This thesis describes a method of deciphering messages encrypted with rotor machines utilising a Genetic Algorithm to search the keyspace. A fitness measure based on the phi test for non randomness of text is described and the results show that an unknown three rotor machine can generally be cryptanalysed with about 4000 letters of ciphertext. The results are compared to those given using a previously published technique and found to be superior. Acknowledgements I would like to thank my supervisors, Vic RaywardSmith and Geoff McKeown, for their help and encouragement. Contents 1 Introduction 8 2 Statistical Inference 10 2.1 Introduction : : : : : : : : : : : : : : : : : : : : : : : : : : : : 10 2.2 Uncertainty : : : : : : : : : : : : : : : : : : : : : : : : : : : : 11 2.2.1 Rules of Probability : : : : : : : : : : : : : : : : : : : 12 2.2.2 Frequency Probability : : : : : : : : : : : : : : : : : : 15 2.2.3 Subjective Probability : : : : : : : : : : : : : : : : : : 15 2.3 Modelling...
Constraint Satisfaction Algorithm for the Automated Decryption of Simple Substitution Ciphers
, 1988
"... This paper describes a systematic procedure for decrypting simple substitution ciphers with word divisions. The algorithm employs an exhaustive search in a large online dictionary for words that satisfy constraints on word length, letter position and letter multiplicity. The method does not rely on ..."
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This paper describes a systematic procedure for decrypting simple substitution ciphers with word divisions. The algorithm employs an exhaustive search in a large online dictionary for words that satisfy constraints on word length, letter position and letter multiplicity. The method does not rely on statistical or semantical properties of English, nor does it use any languagespecific heuristics. The system is, in fact, language independent in the sense that it would work equally well over any language for which a suf ficiently large dictionary exists online. To reduce the potentially high cost of locating all words that contain specified patterns, the dictionary is compiled into a database from which groups of words that satisfy simple constraints may be accessed simultaneously. The algorithm (using a relatively small dictionary of 19,000 entries) has been implemented in Franz Lisp on a Vax 11/780 computer running 4.3 BSD Unix. The system is frequently successful in a completely automated mode  preliminary testing indicates about a 60% success rate, usually in less than three minutes of CPU time. If it fails, there exist interactive facilities, permitting the user to guide the search manually, that perform very well with minor human intervention.
The Automated Cryptanalysis of Analog Speech Scramblers
, 1998
"... An automated method of attacking commonIv used speech scramblers is presented. The cryptanalysis relies on the availability of the scrambled speech only and makes use of the characteristics of speech. It is shown that some of the currently available time and frequency domain scramblers, based on a f ..."
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An automated method of attacking commonIv used speech scramblers is presented. The cryptanalysis relies on the availability of the scrambled speech only and makes use of the characteristics of speech. It is shown that some of the currently available time and frequency domain scramblers, based on a fixed permutation, can be cryp. tanalysed. For systems where the permutation is changed with time, methods for partial recovery of the encrypted speech for several existing systems are given. In the case of the frequency domain scramblers a novel method of attack using a codebook is presented.
Cryptography and Cryptanalysis Through Computational Intelligence
, 2007
"... The past decade has witnessed an increasing interest in the application of Computational Intelligence methods to problems derived from the field of cryptography and cryptanalysis. This phenomenon can be attributed both to the effectiveness of these methods to handle hard problems, and to the major i ..."
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The past decade has witnessed an increasing interest in the application of Computational Intelligence methods to problems derived from the field of cryptography and cryptanalysis. This phenomenon can be attributed both to the effectiveness of these methods to handle hard problems, and to the major importance of automated techniques in the design and cryptanalysis of cryptosystems. This chapter begins with a brief introduction to cryptography and Computational Intelligence methods. A short survey of the applications of Computational Intelligence to cryptographic problems follows, and our contribution in this field is presented. Specifically, some cryptographic problems are viewed as discrete optimization tasks and Evolutionary Computation methods are utilized to address them. Furthermore, the effectiveness of Artificial Neural Networks to approximate some cryptographic functions is studied. Finally, theoretical issues of Ridge Polynomial Networks and cryptography are presented. The experimental results reported suggest that problem formulation and representation are critical determinants of the performance of Computational Intelligence methods in cryptography. Moreover, since strong cryptosystems should not reveal any patterns of the encrypted messages or their inner structure, it appears that Computational Intelligence methods can constitute a first measure of the cryptosystems’ security.