The rotor machine is what many people will think of when they think of a cipher machine. And the most straightforward type of rotor machine is the one invented by Edward Hebern, in the United States.
Here's a very crude artistic impression (in ASCII-Art, yet!) of what this beautifully-made machine looked like:
___
___ '-.
_ ___ '-. \
_ o\_____ ___ '-. \ |______
_ \ | ___ '-. \ | _/\
_ o\ | ___ '-. \ | _/ _ |
/ \ ___ '-. \ | _/ _/o\ \
| O | ___ '-. \ | _/ _/o | |
_/| |.-' '-. \ | _/ _/o o \ \
_/ / \ | _/ _/o o o | |
/_______| |_____ _/ _/o o o _/ _/ === ===
| .-. | /o o o _/ _/ === === ===
| /-. )_________ \ \ o o _/ _/ === === ===|
| ( )________ \ | | o _/ _/ === === ===| |
| \_________ \ ) \ \o _/ _/|=== === ===| |_|
| | ( ) | |/ _/|__|| || || |_|
| .-. | |'-' \ _/|____||__||__||_|
| ( ) _|____|_ | | | |___|
| '-' \ / | |_____|---
| \_____======O===========O/
|________________________________|/
The Japanese cipher machine the American solvers of which called it PURPLE didn't have any rotors in it, but instead used telephone stepping switches. However, in some ways, it was still closely related to a rotor machine, and so it will be discussed here as well.
While the term code as distinct from cipher sometimes refers to a substitution on words and phrases as distinct from one on letters or digraphs, and sometimes (as in "Morse code", "Hamming code", or "Huffman code") seems to be applicable to any fixed substitution, forcing me to employ it somewhat loosely, I have been fastidious in restricting the use of the term "rotor machine" to cipher machines with wired rotors, which operate by changing a substitution produced by wires inside the rotor to its contacts when the rotor is rotated. Other cipher machines, operating on different principles, but with rotating parts (such as the Hagelin lug and pin machines, or the Lorenz SZ-40) which operate on entirely different principles, have occasionally been referred to in print as "rotor machines". I wish to disparage this trend, as it would make the term "rotor machine" much less useful, by causing it no longer to refer to a family of cipher machines which all are based on a common cryptographic principle.
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