## On the Subject of the Differential CM

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

Turn the letter on screen A to a Value via the Value Table, modulo it by the length of the encrypted word. This is your Shift Offset.

Shift the encrypted word to the left a number of times equal to the Shift Offset.

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

#### Encrypt Instructions

• 1: Take the Nth digit on screen 1 and multiply it by 26.
• 2: Then take the alphabetic position (A1Z26) of the (N + 1)th letter of the encrypted word and subtract from it the alphabetic position (A1Z26) of the Nth letter of the encrypted word, modulo 26.
• 3: Sum the 2 numbers you got from steps 1 and 2 to get a 2 digit number. Append this number to any previous digits.
• 4: Repeat steps 1 - 3 for each digit displayed on screen 1.
• 5: Split the string of digits into 2 equal halves, placing the 2nd half of digits under the 1st half.
• 6: Let D be a string of letters, containing only the first letter of the encrypted word.
• 7: Read the Nth column top-to-bottom as a two-digit number.
• 8: Sum the alphabetic position (A1Z26) of the last letter of D and the number you got from step 7, modulo 26, and turn the resulting number into a letter (A1Y25Z0). Append this letter to D.
• 9: Repeat steps 7 - 8 for each column in the digit string.
• 10: Finally, shift the letters in D to the right by the Shift Offset to get your decrypted word.

#### Decrypt Instructions

• 1: Take the Nth digit on screen 1 and multiply it by 26.
• 2: Then take the alphabetic position (A1Z26) of the (N + 1)th letter of the encrypted word and subtract from it the alphabetic position (A1Z26) of the Nth letter of the encrypted word, modulo 26.
• 3: Sum the 2 numbers you got from steps 1 and 2 to get a 2 digit number. Write this number top to bottom, to the right of any previous numbers.
• 4: Repeat steps 1 - 3 for each digit displayed on screen 1.
• 5: Concatenate the top and bottom digits in that order to get a new digit string. Split this digit string into pairs of numbers.
• 6: Let D be a string of letters, containing only the first letter of the encrypted word.
• 7: Sum the alphabetic position (A1Z26) of the last letter of D and the Nth number pair, modulo 26, and turn the resulting number into a letter (A1Y25Z0). Append this letter to D.
• 8: Repeat step 7 for each number pair you got in step 5.
• 9: Finally, shift the letters in D to the right by the Shift Offset to get your decrypted word.

#### Example 1

Encrypted Word: JOHMGBGE
Shift Offset: V → 87 → 7
Screen 1: 1023311
Using Encrypt Rules

JOHMGBGE + 7 → EJOHMGBG

(26 * 1) + ((J - E) MOD 26) → 31
(26 * 0) + ((O - J) MOD 26) → 05
(26 * 2) + ((H - O) MOD 26) → 71
(26 * 3) + ((M - H) MOD 26) → 83
(26 * 3) + ((G - M) MOD 26) → 98
(26 * 1) + ((B - G) MOD 26) → 47
(26 * 1) + ((G - B) MOD 26) → 31

 3 1 0 5 7 1 8 3 9 8 4 7 3 1

(E + 33) MOD 26 → 12 → L
(L + 19) MOD 26 → 5 → E
(E + 08) MOD 26 → 13 → M
(M + 54) MOD 26 → 15 → O
(O + 77) MOD 26 → 14 → N
(N + 13) MOD 26 → 1 → A
(A + 81) MOD 26 → 4 → D

#### Example 2

Encrypted Word: KMVVSF
Shift Offset: R → 7 → 1
Screen 1: 01030
Using Decrypt Rules

KMVVSF + 1 → MVVSFK

(26 * 0) + ((V - M) MOD 26) → 09
(26 * 1) + ((V - V) MOD 26) → 26
(26 * 0) + ((S - V) MOD 26) → 23
(26 * 3) + ((F - S) MOD 26) → 91
(26 * 0) + ((K - F) MOD 26) → 05

 0 2 2 9 0 9 6 3 1 5

(M + 02) MOD 26 → 15 → O
(O + 29) MOD 26 → 18 → R
(R + 09) MOD 26 → 1 → A
(A + 63) MOD 26 → 12 → L
(L + 15) MOD 26 → 1 → A

MORALA + 1 → AMORAL