Breaking Substitution Ciphers Using a Relaxation Algorithm

Substitution ciphers are codes in which each letter
of the alphabet has one fixed substitute, and the word divisions 
do not change.  In this paper the problem of breaking substitution
ciphers is represented as a probabilistic labeling problem.
Every code letter is assigned probabilities of representing plain text
letters.  These probabilities are updated in parallel for all
code letters, using joint letter probabilities.  Iterating the updating
scheme results in improved estimates that finally lead to
breaking the cipher.  The method is applies successfully to two examples.

CACM November, 1979

Peleg, S.
Rosenfeld, A.

Cryptography, substitution ciphers,
probabilistic classification, relaxation

3.42 3.63

CA791103 DB January 23, 1980  11:15 AM

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