 ## On the Subject of the GROMARK CM

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

Create a key using the keyword on screen 1 and the Boolean Expression on screen A. Take the keyword on screen 1 and write numbers underneath it in such a way that the ascending numbers are going in alphabetical order. If there's a tie between letters, then ascend in reading order. Write the alphabet key underneath the number key so that it fits in the columns of the number key in reading order. Read the alphabet key in ascending numerical order to get a new alphabet key. Write a second alphabet above the alphabet key. This will be referred to as the GROMARK Alphabet.

The digit string on screen 2 will be referred to as the Primer Key.

If the Submit Button is white, follow the instructions under Encrypt Instructions. Otherwise follow the instructions under Decrypt Instructions.

#### Encrypt Instructions

• Find the Nth letter of the encrypted word in the top row of the GROMARK Key.
• Go right a number of times equal to the Nth digit of the Primer Key, wrapping around to the top left.
• The letter below this letter becomes your Nth decrypted letter.
• Take the sum of the Nth and (N + 1)th digit of the Primer Key, modulo 10, and write it at the end of the Primer Key.

#### Decrypt Instructions

• Find the Nth letter of the encrypted word in the bottom row of the GROMARK Key.
• Go left a number of times equal to the Nth digit of the Primer Key, wrapping around to the bottom right.
• The letter above this letter becomes your Nth decrypted letter.
• Take the sum of the Nth and (N + 1)th digit of the Primer Key, modulo 10, and write it at the end of the Primer Key.

Do this for each letter of the encrypted word and the keyword to get your decrypted word.

#### Example 1

Encrypted Word: ACPBT
Alphabet Key: NEDLSABCFGHIJKMOPQRTUVWXYZ
Primer: 71
Using Encrypt Rules

NEEDLESS
62315478
NEDLSABC
FGHIJKMO
PQRTUVWX
YZ
DEEELNSS
12345678
LEDASNBC
IGHKJFMO
TQRVUPWX
ZY
 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z L I T E G Q Z D H R A K V S J U N F P Y B M W C O X

A + 7 → H → D
C + 1 → D → E
P + 8 → X → C
B + 9 → K → A
T + 7 → A → L

Decrypted Word: DECAL

#### Example 2

Encrypted Word: FTDGSA
Alphabet Key: GUIDEABCFHJKLMNOPQRSTVWXYZ
Primer: 71968
Using Decrypt Rules

GUIDE
35412
GUIDE
ABCFH
JKLMN
OPQRS
TVWXY
Z
DEGIU
12345
DEGIU
FHACB
MNJLK
RSOQP
XYTWV
Z
 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z D F M R X E H N S Y G A J O T Z I C L Q W U B K P V

F - 7 → W → U
T - 1 → O → N
D - 9 → C → R
G - 6 → X → E
S - 8 → D → A
A - 8 → R → D