6.2 ROTOR SYSTEMS
A rotor system incorporates more than one rotor sharing the same axis of rotation. The rotor system shown in Figure 6.3 produces the polyalphabetic substitution, which is a composition of the r substitutions θ0, θ1, …, θr−1 (Fig. 6.4).
If each of the r rotors are rotated counterclockwise k0, k1, …, kr−1 positions (relative to their benchmarks), the substitution
is replaced by
It is intended that the position of at least one rotor changes after the encipherment of each plaintext letter in a rotor system. The position of the jth rotor for the encipherment of the ith plaintext letter is determined by a rotational displacement function kj(i) so that
The simplest rotational displacement functions {kj(i)} are (modulo m), with m = 26. This is analogous to an automobile's ...
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