Title :
Breaking substitution cyphers using stochastic automata
Author :
Oommen, B.J. ; Zgierski, J.R.
Author_Institution :
Sch. of Comput. Sci., Carleton Univ., Ottawa, Ont., Canada
fDate :
2/1/1993 12:00:00 AM
Abstract :
Let Λ be a finite plaintext alphabet and V be a cypher alphabet with the same cardinality as Λ. In all one-to-one substitution cyphers, there exists the property that each element in V maps onto exactly one element in Λ and vice versa. This mapping of V onto Λ is represented by a function T*, which maps any v∈V onto some λ∈Λ (i.e., T*(v)=λ). The problem of learning the mapping of T* (or its inverse (T *)-1) by processing a sequence of cypher text is discussed. The fastest reported method to achieve this is a relaxation scheme that utilizes the statistical information contained in the unigrams and trigrams of the plaintext language. A new learning automaton solution to the problem called the cypher learning automaton (CLA) is given. The proposed scheme is fast, and the advantages of the scheme in terms of time and space requirements over the relaxation method have been listed. Simulation results comparing both cypher-breaking techniques are presented
Keywords :
cryptography; learning systems; relaxation theory; stochastic automata; automaton solution; cardinality; cypher alphabet; cypher learning automaton; finite plaintext alphabet; learning; relaxation scheme; statistical information; stochastic automata; substitution cyphers; trigrams; unigrams; Art; Councils; Cryptography; Decoding; Heart; Intelligent systems; Learning automata; Natural languages; Relaxation methods; Stochastic processes;
Journal_Title :
Pattern Analysis and Machine Intelligence, IEEE Transactions on