  Structural properties of two well-known families of keystream generators,
Shrinking Generators and Cellular Automata, have been analyzed. Emphasis is on
the equivalence of the binary sequences obtained from both kinds of generators.
In fact, Shrinking Generators (SG) can be identified with a subset of linear
Cellular Automata (mainly rule 90, rule 150 or a hybrid combination of both
rules). The linearity of these cellular models can be advantageously used in
the cryptanalysis of those keystream generators.
