My entry for RC2017/04, An Enigma Machine Z30 Simulator running on a Kim 1 / Uno

Just noticed this years retrochallenge is up! http://www.retrochallenge.org/

Here is the entry page:
http://www.retrochallenge.org/2017/03/rc201704-open-for-entrants.html

1. Your name (or alias);
2. Your Twitter handle (if applicable);
3. Your blog location (for project updates); and
4. A brief synopsis of your project.

And here is my entry:

1) Arduino Enigma

2) @ArduinoEnigma
     https://twitter.com/arduinoenigma

3) http://arduinoenigma.blogspot.com/

4) There are some cool kids out there making electronic versions of the Enigma Machine. They mostly seem to be some sort of microcontroller wired to 4x fourteen segment displays and pushbuttons to move the rotors and type the message to encrypt. I wanted to do the same but without rolling a custom PCB. A KIM Uno was laying around, having been used only to develop a 53 byte clock program. The idea was born to use the KIM to simulate an Enigma Machine. This 6502 program implements a 1930s encryption machine in a 1970s computer. It turns a KIM Uno into the cheapest physical enigma machine simulator out there.

The original, lever stepping only version was 703 bytes including the menu to change the encryption settings. The v2 gear and lever stepping enigma engine has already been optimized to be smaller than v1. The v2 menu system gained a third function to set the stepping mode. After optimizations, the feature richer v2 is now only 11 bytes bigger than v1.

The goal for this retrochallenge is to further optimize the code so its total size is smaller than v1.

For a bit of background, three rare, numbers only, Enigma Z30 were found in Sweden, an article in Cryptologia "Enigma Z30 retrieved" describes the wheel wiring. This machine can only encrypt numbers and the rotors have only 10 positions, it is thus perfect to be simulated in a KIM.Based on the published wheel wiring and some reasonable assumptions based on the architecture of other enigma machines, a 6502 program was written. The program has two parts, the core enigma functionality, the user being responsible for changing the machine settings via direct RAM manipulation using the KIM monitor and a menu system for a user friendly way of changing the machine settings. After learning that two versions of the machine existed, one with double stepping anomaly prone lever stepping and another with odometer like geared stepping, the program and its menu system ware modified to also support gear stepping.

Below are some demo videos of v1.

https://www.instagram.com/p/BOu3_X8h1rD/
https://www.instagram.com/p/BNbAu1Xhsde/
https://www.instagram.com/explore/tags/enigmaz30/

I had been looking for an excuse to make a new video of v2 showing the new F3 mode to select the stepping mechanism type and to shave a few more bytes off.

RC2017/04, here we come...