## On the Subject of The Inverted Cornflower Cipher

Centaureae cyani colores pulchros habent.

On the module, you will see 3 screens, a keyboard, 2 arrows, and a submit button that displays the current page you’re on.

Pressing the right arrow takes you to the next page. Pressing the left arrow takes you to the previous page. There is a total of 2 pages.

To prepare, interpret the first character of the serial number as a base-36 digit and convert it to a 6-digit binary number. This manual will refer to the individual digits of this binary number as “bit 1”, “bit 2”, “bit 4”, “bit 8”, and “bit 16”. (Bit 32 is not used.)

### Step 1: Ping-pong Straddling Checkerboard Cipher

For this step, concatenate the last screen on page 1 and the first screen on page 2. We will refer to this as the “coded word”. You will also need the words on the middle and bottom screens on page 2, called KW1 and KW2, respectively.

In this step, we will create two straddling checkerboards. We will use the first one to convert the coded word into a bunch of digits, and the second to convert those digits back into letters.

For the first straddling checkerboard, obtain the following numbers:

- d1 = number of indicators, modulo 6
- d2 = number of ports, modulo 6; if equal to d1, add 1 and modulo 6 again

Also create an alphabet key from KW1 as follows:

- Remove all duplicate letters from the keyword (retain first occurrences).
- Write the entire alphabet with the letters from the keyword removed.
- If bit 8 is 1, place the alphabet after the keyword, otherwise before.

To create a straddling checkerboard, start with 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 bit 16 is 1, use column order (fill the first column from top to bottom, then the second column etc.); otherwise, use reading order.

Also label the rows except the first with the numbers 0–5 but omitting d1 and d2.