## On the Subject of the Ping-pong Straddling Checkerboard CM

A machine that knows no bounds when it comes to ciphers.

Create a straddling checkerboard by following the instructions below:

- Create a key using the keyword on screen 1 and the Left Boolean Expression on screen 3.
- Convert the letter on screen A to a Value via the Value Table, modulo 6. This will be referred to as D1.
- Convert the letter on screen B to a Value via the Value Table, modulo 6. This will be referred to as D2. If it is equal to D1, add 1 and modulo 6 again.
- Create a table with 5 rows and 6 columns. Label the columns with the numbers 0–5. Cross out all the first-row cells except for those in columns labeled D1 and D2.
- Fill the remaining 26 cells with the alphabet key. If the Right Boolean Expression on screen 3 is true, use column order (fill the first column from top to bottom, then the second column etc.); otherwise, use reading order.
- This will be referred is as Checkerboard A.

Create Checkerboard B by following the steps above but with these screens instead: Keyword on screen 2, Left Boolean Expression on screen 4, Letter on screen C (D3), Letter on screen D (D4), Right Boolean Expression on screen 4.

Convert every letter of the encrypted word to digits via Checkerboard A. Each letter that occurs in the first row gets turned into the single digit that labels its column; all other letters turn into digits labeling the row followed by the column.

Convert the string of digits back into letters via Checkerboard B. If the first digit is D3 or D4, use the corresponding letter from the first row. Otherwise, use a pair of digits, where the first identifies the row and the second the column, to obtain a letter.