Folder:
Mode:

GGG PAPER MACHINE


COAST GUARD

Use top position as bench mark

The USCG Paper Cipher Machines

These were field reproductions of captured Enigma rotor wirings, hand-drawn on manilla file folders by analysts at the U.S. Coast Guard's cryptanalytic unit (OP-20-G). Each folder represented a different daily key configuration. The "bench mark" — the red pencil line across one row — was the current rotor setting.
The Coast Guard Cryptanalytic Unit, led by Elizebeth Smith Friedman from the late 1930s through 1945, broke Axis diplomatic and smuggling traffic using paper methods like this one. The original folders are preserved at the National Archives and the National Cryptologic Museum.

The Substitution Table

Each vertical column is a rotor "strip." For a given input letter (listed on the left), find its row, then read across to the column of the rotor you're using. The lowercase letter in that cell is the substitution. The red pencil line marks the current bench mark — the starting row for each new character. With each keystroke, the right-most strip's bench mark moves down one row.
The tiny red numerals in the corner of each cell are the absolute position (0–25). The handwritten letters are the historical Enigma rotor wirings (I through V) laid out in paper-strip form. Setting the bench mark row is equivalent to setting the rotor window letter on a mechanical Enigma.
Strip A
RIGHT · FAST
A

Strip A — Right (Fast) Rotor

Advances by one position on every keystroke. This is the fastest-moving rotor and governs the letter-to-letter variation.
Strip B
MIDDLE
A

Strip B — Middle Rotor

Advances one position when Strip A passes its notch letter — roughly once every 26 keystrokes. The "double-step" on this rotor is the source of Enigma's famous stepping quirk.
Strip C
LEFT · SLOW
A

Strip C — Left (Slow) Rotor

Advances one position when Strip B passes its notch — roughly once every 676 keystrokes. Changes rarely during a typical message.
Reflector
UMKEHRWALZE

Reflector

A fixed wiring that sends the signal back through the rotors in reverse. Makes the machine self-reciprocal: same settings encrypt and decrypt.
—
—

Reset

Returns all strips to A-A-A and clears the message. Use before each new message.
Plain:
Cipher:
Keystrokes: 0 · Last: — → —

Receive from Enigma

Paste the ciphertext received over the air. Before decoding, make sure the folder's rotor/reflector/positions match what the sender used.

Send to Enigma

Type the plaintext. The paper machine encrypts it. Hand the ciphertext (and settings) to the Enigma operator.

FILED · OP-20-G S-3591
checked 2-G by analysis
F-3591
KEYS — type or click

Keyboard

Click a key or type on your physical keyboard. Each keypress advances Strip A by one position before enciphering. The ciphered output letter appears in the Cipher line above.
The German layout is QWERTZ — Z and Y are swapped vs. the American QWERTY.