A public-key cryptosystem based essentially on ideas coming from L systems was introduced in (Salomaa and Welzl, 1983), see also (Salomaa, 1985) and (Salomaa, 1984). The system was further investigated in (Baunwall, Bertelsen and Weibel, 1986) and (Koskinen and Salomaa, 1985). The purpose of the present paper is to study the system, both from mathematical and cryptanalytic point of view. In particular, we investigate cryptanalytic approaches and what one can accomplish by preprocessing. We also discuss the desirable properties of the underlying DT0L system such as different types of backward determinism and the role of growth. The system is very flexible in many respects, for instance, as regards the plaintext blocksize.
