D. Andelman and J. Reeds. On the cryptanalysis of rotor machines and substitution-permutation networks. IEEE Transactions on Information Theory, IT-28(4), 1982.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....have embedded keyspace K in Y . We now wish to maximise the likelihood function L(Xjy) n Gamma1 Y i=0 e 0 y i S(R(i) X)p over Y , with the anticipation that the estimate produced will be in the vicinity of Pi. The MLE, X, exists and is strongly consistent i.e. X Pi as n 1 (see [1]) We now need some method to find X. 1] suggests using an iterative algorithm based on the following result. 87 Theorem Let F(Z) be a polynomial with non negative coefficients, homogeneous of degree d in its variables z ij . Let Z = fz ij : z ij 0; q Gamma1 X i=0 z ij = 1g; and ....

....to maximise the likelihood function L(Xjy) n Gamma1 Y i=0 e 0 y i S(R(i) X)p over Y , with the anticipation that the estimate produced will be in the vicinity of Pi. The MLE, X, exists and is strongly consistent i.e. X Pi as n 1 (see [1] We now need some method to find X. [1] suggests using an iterative algorithm based on the following result. 87 Theorem Let F(Z) be a polynomial with non negative coefficients, homogeneous of degree d in its variables z ij . Let Z = fz ij : z ij 0; q Gamma1 X i=0 z ij = 1g; and define the transformation T : Z Z by T (Z) ....

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D. Andelman and J. Reeds. On the cryptanalysis of rotor machines and substitution-permutation networks. IEEE Transactions on Information Theory, IT-28(4), 1982.

....an acceptable error probability and then search this key class in order to determine the key more quickly than would be expected in an exhaustive key search. For certain block ciphers it is also possible to maximise or calculate the likelihood function very efficiently. Andelman and Reeds [1] [2] considered such a situation for both rotor machines (stream ciphers) and SP networks (block ciphers) For an SP network with a small number of rounds and an n bit key k = k 1 ; Delta Delta Delta ; k n ) the likelihood function for k is well approximated by a product of functions each ....

D. Andelman and J. Reeds. On the Cryptanalysis of Rotor Machines and Substitution--Permutation Networks. IEEE Transactions on Information Theory, IT-28:578--584, 1982.

....large discrete keyspace of a rotor machine, of magnitude up to (26 ) 3 , using a simple statistical measure of suitability. The method involves finding the last rotor of a three rotor machine using a GA and then solving the resulting two rotor machine using the iterative technique described in [1]. The plaintext is assumed to be n independent realisations of a random variable defined on alphabet Z q , with probability distribution derived from observation of the single letter frequencies of English. The distribution we use is that given in [7] The statistical measure of fitness is based ....

....find an estimate of k, k, given a string of ciphertext. 3 CRYPTANALYSIS OF A THREE ROTOR MACHINE Our method of attack is to find the last rotor of a three rotor machine using a Genetic Algorithm (GA) and then to solve the resulting two rotor machine using the iterative technique described in [1]. 3.1 GENETIC ALGORITHMS We implemented the problem on the X GAmeter toolkit [9] developed at the UEA, which enables the easy use of GAs on a variety of problems. The decisions in implementing a GA for a particular problem are concerned with representation, fitness evaluation and the select, ....

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D. Andelman and J. Reeds. On the cryptanalysis of rotor machines and substitution-permutation networks. IEEE Transactions on Information Theory, IT-28(4), 1982.

....their new ciphertext only attack on filter generators, Cain and Sherman [16, 17] apply a language recognition subroutine to detect when they have discovered part of the initial fill. Related statistical techniques are also useful in breaking the Hagelin cryptograph [75] and various rotor machines [2]. Despite the importance of recognizing valid plaintext, the cryptologic literature provides little practical advice on how to automate this task. Language recognition for cryptanalysis must deal with the following three constraints. First, cryptology is adversarial in nature. Therefore, the ....

Andelman, Dov; and James Reeds, "On the cryptanalysis of rotor machines and substitutionpermutation networks," IEEE Transactions on Information Theory, IT-28:4 (July 1982), 578--584.

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