CA-1.0 performs encryption in two rounds. Each round is composed of two subrounds, a left-subround an a right-subround. Each subround, in turn, is divided into two phases: a substitution phase and a diffusion phase. The relationship of these rounds, subrounds, and phases is shown in figure 5. In this figure the diffusion phases are labeled D and the substitution phases are labeled S. A link label enclosed in a box in this figure indicates that the link has just undergone link encryption. Links labeled without a box must undergo link encryption before being used to drive the diffusion phase of the next subround. The link areas are hatched, and the block areas unhatched. The bar representing the suppressed first substitution phase is gray.
The diffusion phase is accomplished by iteration of an irreversible CA, while the substitution phase is accomplished by a reversible CA. These phases have complementary cryptographic functions. Their properties are summarized in table 5. For further details refer to the next section.
Table 5: Summary of differences between diffusion and substitution phases.