Introduction

To simulate a "hard wired" rotor substitution cipher, a Python list is used. A list-index is the input (character) and the list-value is the output substituted list-index (character).

For a rotor to be a substitution cipher we create a randomized list from an ordered list. (Note: the lists contain list-indexes and no actual character.)

In order to simulate an enigma machine correctly, a character can not be encoded to itself. In other words 'A' can not be substituted for 'A'. It must be a different character.

I created this code to make sure 'A' is not be substituted for 'A'. I searched the web for an hour looking for a existing solution but gave up. So here is my code (such as it is).

I left my print statement in the code. I used them to see what was going on in the code. Comment them out or delete them or use them to see what is going on.

This is not the best/cleanest code. someday I will fix it. For now it is good enough to continue with the enigma machine project.

Randomization Process

The Algorithm

Each character at the top of the ordered list (abclst) is replaced in the randomized list (ranlst) from the remaining characters (in the ordered list abclst).

After being added to the randomized list, the top character replaces the randomly selected character in the ordered list. It can now be selected for inclusion in the random list.

The process continues with the next top character in the ordered list. When there are only two characters left in the ordered list, they are handled differently. See the code.