Cipher Machine

On the Subject of the ElsieFour 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. Make sure to remove any Zs. Rearrange the key into a 5×5 matrix.

Take the letter displayed on screen B and label it the Marked Letter.

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

Encrypt Instructions

Take the Marked Letter’s alphabetic position, minus 1 (A0Y24) and modulo it by 5. This will be called R.
Take the Marked Letter’s alphabetic position, minus 1 (A0Y24) and divide it by 5, rounding down. This will be called D.
Find the Nth letter of the encrypted word in the Matrix and go right an R amount of times and down an D amount of times, wrapping around if needed.
The letter you end up on becomes your Nth decrypted letter.
Shift the row to the right that contains the Nth decrypted letter.
Shift the column down that contains the Nth encrypted letter.
Take the encrypted letter's alphabetic position, minus 1 (A0Y24) and modulo it by 5. This will be called R.
Take the encrypted letter's alphabetic position, minus 1 (A0Y24) and divide it by 5, rounding down. This will be called D.
Find the Marked Letter in the Matrix and go right an R amount of times and down an D amount of times, wrapping around if needed.
The letter you end up on becomes your new Marked Letter.

Decrypt Instructions

Take the Marked Letter’s alphabetic position, minus 1 (A0Y24) and modulo it by 5. This will be called L.
Take the Marked Letter’s alphabetic position, minus 1 (A0Y24) and divide it by 5, rounding down. This will be called U.
Find the Nth letter of the encrypted word in the Matrix and go left an L amount of times and up an U amount of times, wrapping around if needed.
The letter you end up on becomes your Nth decrypted letter.
Shift the row to the right that contains the Nth decrypted letter.
Shift the column down that contains the Nth encrypted letter.
Take the encrypted letter's alphabetic position, minus 1 (A0Y24) and modulo it by 5. This will be called R.
Take the encrypted letter's alphabetic position, minus 1 (A0Y24) and divide it by 5, rounding down. This will be called D.
Find the Marked Letter in the Matrix and go right an R amount of times and down an D amount of times, wrapping around if needed.
The letter you end up on becomes your new Marked Letter.

Finally, if any of the letters on screen 2 match at the same position as any of the letters of your encrypted word, replace that letter with a Z. You should now have an decrypted word.

Example 1

Encrypted Word: QHRNI
Marked Letter: T
Screen 2: CVMEN
Using Encrypt Rules

B	C	E	F	G
H	J	K	L	N
O	Q	S	T	U
V	W	X	P	Y
R	A	M	I	D

T → 19 → R4 D3
Q + R4 + D3 → B

B

C

E

F

G

B

C

E

F

G

A

C

E

F

H

J

K

L

N

H

J

K

L

N

H

B

K

L

N

O

Q

S

T

U

O

Q

S

T

U

O

J

S

T

U

V

W

X

P

Y

V

W

X

P

Y

V

Q

X

P

Y

R

A

M

I

D

R

A

M

I

D

R

W

M

I

D

Q → 16 → R1 D3
T + R1 + D3 → F

F → 5 → R0 D1
H + R0 + D1 → O

G

A

C

E

F

G

A

C

E

F

R

A

C

E

F

H

B

K

L

N

H

B

K

L

N

G

B

K

L

N

O

J

S

T

U

O

J

S

T

H

O

J

S

T

V

Q

X

P

Y

V

Q

X

P

Y

U

Q

X

P

Y

R

W

M

I

D

R

W

M

I

D

V

W

M

I

D

H → 7 → R2 D1
F + R2 + D1 → B

B → 1 → R1 D0
R + R1 + D0 → A

R

A

C

E

F

R

A

C

E

F

W

A

C

E

G

B

K

L

N

G

B

K

L

N

G

R

K

L

N

H

O

J

S

T

H

O

J

S

T

H

B

J

S

T

U

Q

X

P

Y

U

Q

X

P

Y

U

O

X

P

Y

V

W

M

I

D

V

W

M

I

D

V

Q

M

I

D

R → 17 → R2 D3
B + R2 + D3 → C

C → 2 → R2 D0
N + R2 + D0 → R

F

W

A

C

E

F

W

A

C

E

V

W

A

C

E

G

R

K

L

N

G

R

K

L

F

G

R

K

L

H

B

J

S

T

H

B

J

S

T

N

B

J

S

T

U

O

X

P

Y

U

O

X

P

Y

H

O

X

P

Y

V

Q

M

I

D

V

Q

M

I

D

U

Q

M

I

D

N → 13 → R3 D2
C + R3 + D2 → B

B → 1 → R1 D0
I + R1 + D0 → D

BOARD + CVMEN → BOARD
Decrypted Word: BOARD

Example 2

Encrypted Word: XOYQ
Marked Letter: D
Screen 2: SLNY
Using Decrypt Rules

A	B	C	F	G
H	J	K	M	N
O	Q	R	T	V
W	X	Y	S	U
P	L	I	E	D

D → 3 → L3 U0
X + L3 + U0 → S

A

B

C

F

G

A

B

C

F

G

A

B

I

F

G

H

J

K

M

N

H

J

K

M

N

H

J

C

M

N

O

Q

R

T

V

O

Q

R

T

V

O

Q

K

T

V

W

X

Y

S

U

W

X

Y

S

U

W

R

Y

S

P

L

I

E

D

P

L

I

E

D

P

L

X

E

D

X → 23 → R3 D4
D + R3 + D4 → R

R → 17 → L2 U3
O + L2 + U3 → E

A

B

I

F

G

A

B

I

F

G

D

B

I

F

G

H

J

C

M

N

H

J

C

M

N

A

J

C

M

N

O

Q

K

T

V

O

Q

K

T

V

H

Q

K

T

V

U

W

R

Y

S

U

W

R

Y

S

O

W

R

Y

S

P

L

X

E

D

P

L

X

E

U

P

L

X

E

O → 14 → R4 D2
R + R4 + D3 → B

B → 1 → L1 U0
Y + L1 + U0 → R

D

B

I

F

G

D

B

I

F

G

D

B

I

F

E

A

J

C

M

N

A

J

C

M

N

A

J

C

M

G

H

Q

K

T

V

H

Q

K

T

V

H

Q

K

T

N

O

W

R

Y

S

O

W

R

Y

S

O

W

R

V

U

P

L

X

E

U

P

L

X

E

U

P

L

X

Y

Y → 24 → R4 D4
B + R4 + D4 → U

U → 20 → L0 U4
Q + L0 + U4 → O

SERO + SLNY → ZERO
Decrypted Word: ZERO

You can use the table below to get the values for moving Up/Right/Down/Left. Find the letter in the table and the column will be the horizontal movement while the row will be the vertical movement.

LR > ----- DU v	0	1	2	3	4
0	A	B	C	D	E
1	F	G	H	I	J
2	K	L	M	N	O
3	P	Q	R	S	T
4	U	V	W	X	Y