Making the most of two heuristics: breaking transposition ciphers with ants
Russell, M.D.
Clark, J.A.
Stepney, S.
Dept. of Comput. Sci., York Univ., UK;
This paper appears in: Evolutionary Computation, 2003. CEC '03. The 2003 Congress on
Publication Date: 8-12 Dec. 2003
Volume: 4,
On page(s): 2653- 2658 Vol.4
ISSN:
ISBN: 0-7803-7804-0
INSPEC Accession Number: 8088196
Digital Object Identifier: 10.1109/CEC.2003.1299423
Current Version Published: 2004-05-24
Abstract
Multiple anagramming is a general method for the cryptanalysis of transposition ciphers, and has a graph theoretic representation. Inspired by a partially mechanised approach used in World War II, we consider the possibility of a fully automated attack. Two heuristics based on measures of natural language are used - one to recognise plaintext, and another to guide construction of the secret key. This is shown to be unworkable for cryptograms of a certain difficulty due to random variation in the constructive heuristic. A solver based on an ant colony optimisation (AGO) algorithm is then introduced, increasing the range of cryptograms that can be treated; the pheromone feedback provides a mechanism for the recognition heuristic to correct the noisy constructive heuristic.
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