A cryptanalytic observation concerning systems based on language theory

This note discusses a cryptanalytic method applicable to some public-key cryptosystems based on the theory of formal languages. Essentially, the method uses the fact that the image of a regular language under an inverse finite substitution is accepted by a finite automation of the same size as the automaton accepting the original regular language. In particular, systems based on iterated morphisms and repeated finite substitutions, 2,3], will be discussed.