## On the Subject of the Coral Cipher

"Coral!" - Rick Grimes

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.

On page 1, the top screen shows a 6 letter encrypted word, the middle screen displays an keyword, and the bottom screen shows a number.

The top screen of page 2 displays another keyword.

Follow the mechanics down below to decrypt your word:

### Step 1: Prissy Cipher

Take the keyword from the middle screen on page 1, remove any duplicate letters while keeping the 1st occurrence. Take the entire alphabet and remove all the letters shown in the keyword.

If the number of ports is odd, put the alphabet at the end of the keyword. Otherwise, put the alphabet in front of the keyword. Then split the key in half, placing the 2nd half underneath the 1st half.

Starting with an offset of the serial number's 4th character (A = 1,B = 2...Z = 26), modulo 13, do the following instructions for each letter of the encrypted word:

• Find the Nth letter of the encrypted word in the key.
• Go left a number times equal to the offset, wrapping around to the right side of the same row.
• The letter above/below where you ended up becomes your new encrypted letter.
• Take the sum of the offset and the resulting letter, modulo 13.

#### Example

Encrypted Word: NKUICV
Key: EARNSTBCDFGHIJKLMOPQUVWXYZ
Offset: V -> 22 -> 9

N -> C -> U Offset: 9 + 21 -> 30 -> 4
K -> X -> G Offset: 4 + 7 -> 11
U -> W -> F Offset: 11 + 6 -> 17 -> 4
I -> D -> V Offset: 4 + 22 -> 26 -> 0
C -> C -> U Offset: 0 + 21 -> 21 -> 8
V -> J -> E

New Encrypted Word: UGFVUE

### Step 2: AMSCO Transposition

Take the number key on the bottom screen on page 1 and place 4 'cells' underneath it so that it fits in the columns of the key in reading order.

If the 1st character of the serial number (A = 10,B = 11...Z = 35) is odd, the cells in reading order have string lengths of {1, 2, 1, 2}. Otherwise, the cells in reading order have string lengths of {2, 1, 2, 1}.

Fill each cell with dashes equal to their string lengths. Place each letter of the encrypted word you got from step 1 in ascending numerical order, replacing each dash in the cells underneath the number. Then read the letters in reading order to get a new encrypted word.

#### Example

Encrypted Word: UGFVUE
Key: 231
String lengths: 1212

 2 3 1 - -- - --
 2 3 1 G UE U FV

New Encrypted Word: GUEUFV

### Step 3: GROMARK Cipher

For this, you will need the encrypted word you got from step 2 and the key from the top screen on page 2.

Write numbers under the keyword in such a way that the ascending numbers are going in alphabetical order. If there's a tie between letters, then accend in reading order.

Now take the keyword and remove any duplicate letters while keeping the 1st occurrence. Take the entire alphabet and remove all the letters shown in the keyword.

If the number of ports, modulo 4, is greater than or equal to 2, put the alphabet at the end of the keyword. Otherwise, put the alphabet in front of the keyword.

Write the alphabet key underneath the number key so that it fits in the columns of the key in reading order. Read the alphabet key in ascending numerical order to get your final alphabet key. Write a second alphabet underneath the alphabet key.

Create a new number key by taking the 1st 3 digits of the number key, and add 3 more numbers to the end of it by summing the 1st 2 numbers, modulo 10, then the 2nd 2 numbers, modulo 10, etc.

For each letter of the encrypted word, do the following:

• Find the Nth letter of the encrypted word in the top alphabet.
• Go left a number of times equal to the Nth digit of the number key.
• The letter below becomes your decrypted letter.

#### Example

Encrypted Word: GUEUFV Keyword: IMAGINED

IMAGINED
57146832

 5 7 1 4 6 8 3 2 B C F H J K L O P Q R S T U V W X Y Z I M A G N E D

Final Alphabet Key: FRZOWNLVGHSIBPXEJTMCQYDKUA

Number Key: 571 -> 571283

G, 5 -> O -> D
U, 7 -> T -> R
E, 1 -> X -> O
U, 2 -> D -> W
F, 8 -> M -> S
V, 3 -> W -> E

Decrypted Word: DROWSE

Once you finally have your decrypted word, you can submit it. Once you start typing, all the screens will go black and the bottom screen will show what you are typing.

To clear it, just click one of the arrows. This goes to one of the pages and clears any input you put in. It will not let you go over 6 letters on input.

Once you are satisfied with your input, press the button labeled "SUB" to submit your answer. On a strike, the module will go back to the first page of the module, but it does not regenerate.