RED: 1st Problem

Munitions Buildings, Washington D.C.

13 May 1935

Mr Firedman,

At your request, we wrote a small report on the
operation of the encryption machine used by the
Japanese diplomacy and whose code name is RED. We
also added an example of encryption and the key
used to achieve it. We also created a cardboard
device that simulates the machine's operation
waiting a replica. We also give a diagram of this
replica

Frank B. Rowlett & Solomon Kullback

THE RED CIPHER MACHINE

==============================

The Red cipher machine consists of a keyboard, a
first plugboard, an interrupter wheel, a large
alphabet wheel, a small alphabet wheel, a
reversing gear, a second plugboard, a lampboard
and a operating handle.

The two alphabet wheels are half-rotors (invented
by the Swedish A.G. Damm). The small alphabet wheel
scrambled the vowels and the large alphabet wheel
scrambled the consonants.

The interrupter wheel has 47 Pins which control
advancement of the two other wheels (vowel and
consonant ones). Some Pins can be removed:
5, 6, 11, 12, 17, 20, 30, 31, 34, 39, 40

Normally, the interrupter wheel advances one step
after each letter was ciphered. If a pin is removed,
the interrupter wheel advances one more step. If
two consecutive pins are removed, the wheel
advances three steps. If the Pins setting is
10111111101, then the Pin number 6 and Pin number
39 have been removed.

In encipher mode, the electrical current starts
from the pressed key (the plain letter) on the
keyboard. It goes through the first plugboard.
Then the current passes either through the vowel
half-rotor or by the consonant half-rotor. Then the
current passes through the second plugboard which
must be set as the inverse of the first plugboard.
The current ends at the printer and a letter is
printed (the ciphered letter). If the plugboards
doesn't mixed the vowels and consonants, the vowel
half-rotor scrambled only vowels and the
consonant half-rotor scrambled only consonant.
But, the first plugboard can associate a consonant
with one input connected to the vowel half-rotor or
it can associate a vowel with one input connected to
the consonant half-rotor.

The following plugboard setting does'nt scramble
letters. The six first letters are connected to the
inputs of the vowel half-rotor (sixes), the
remaining twenty letters are connected to inputs
of the consonant half-rotor (twenties).

AEIOUYBCDFGHJKLMNPQRSTVWXZ

Before March 1934, only vowels could be connected
to the vowel half-rotor and only consonants could
be connected to the consonant half-rotor). After
March 1934, the plugboard setting allows there are
a mixed of vowels and consonants connected to each
half-rotor.

Normally, the machine is configured in direct mode.
If we configure the machine in reverse mode, the
wheels advance in the opposite direction.

The indicator system

-----------------------------

The Pins setting and plugboard setting change
every ten days. A five digits indicator specifies
one of 240 wheels setting (the starting position of
the three wheels). If the first digit begins by

0,1,2,3 or 4, the machine is set in direct mode and

otherwise in reverse mode.

The Half-rotor wiring

------------------------------

Vowel Half-Rotor wiring:

0 1 2 3 4 5

A E I O U Y

1 : 4 2 3 0 5 1

2 : 3 1 2 5 4 0

3 : 2 0 1 4 3 5

4 : 1 5 0 3 2 4

5 : 0 4 5 2 1 3

6 : 5 3 4 1 0 2

Consonant Half-Rotor wiring:

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

B C D F G H J K L M N P Q R S T V W X Z

1 : 12 15 4 16 10 17 6 3 1 7 19 5 18 0 2 13 11 14 8 9

2 : 11 14 3 15 9 16 5 2 0 6 18 4 17 19 1 12 10 13 7 8

3 : 10 13 2 14 8 15 4 1 19 5 17 3 16 18 0 11 9 12 6 7

4 : 9 12 1 13 7 14 3 0 18 4 16 2 15 17 19 10 8 11 5 6

5 : 8 11 0 12 6 13 2 19 17 3 15 1 14 16 18 9 7 10 4 5

6 : 7 10 19 11 5 12 1 18 16 2 14 0 13 15 17 8 6 9 3 4

7 : 6 9 18 10 4 11 0 17 15 1 13 19 12 14 16 7 5 8 2 3

8 : 5 8 17 9 3 10 19 16 14 0 12 18 11 13 15 6 4 7 1 2

9 : 4 7 16 8 2 9 18 15 13 19 11 17 10 12 14 5 3 6 0 1

10 : 3 6 15 7 1 8 17 14 12 18 10 16 9 11 13 4 2 5 19 0

11 : 2 5 14 6 0 7 16 13 11 17 9 15 8 10 12 3 1 4 18 19

12 : 1 4 13 5 19 6 15 12 10 16 8 14 7 9 11 2 0 3 17 18

13 : 0 3 12 4 18 5 14 11 9 15 7 13 6 8 10 1 19 2 16 17

14 : 19 2 11 3 17 4 13 10 8 14 6 12 5 7 9 0 18 1 15 16

15 : 18 1 10 2 16 3 12 9 7 13 5 11 4 6 8 19 17 0 14 15

16 : 17 0 9 1 15 2 11 8 6 12 4 10 3 5 7 18 16 19 13 14

17 : 16 19 8 0 14 1 10 7 5 11 3 9 2 4 6 17 15 18 12 13

18 : 15 18 7 19 13 0 9 6 4 10 2 8 1 3 5 16 14 17 11 12

19 : 14 17 6 18 12 19 8 5 3 9 1 7 0 2 4 15 13 16 10 11

20 : 13 16 5 17 11 18 7 4 2 8 0 6 19 1 3 14 12 15 9 10

Encipherment examples
--------------------------------

First example, a detailled one:

We suppose that we want to encrypt the word “each”.
For now, we ignore the Plugboard.
We start with the three wheels at position 1.

Interrupter wheel: 1, V. wheel: 1, C. wheel : 1
Plain letter “E”, the Vowel Half-Rotor translates
the “E” into “I” (the vowel 2 [in fact, the third])

After the encipherment, the interrupter advances
of one step and consequently, the two other wheels
advance too (of one step).

Interrupter wheel: 2, V. wheel: 2, C. wheel: 2
Plain letter "A", the Vowel Half-Rotor translates
the "A" into "O" (the vowel 3 [in fact, the fourth])

After the encipherment, the interrupter advances
of one step and consequently, the two other wheels
advance too (of one step).

Interrupter wheel: 3, V. wheel: 3, C. wheel: 3

Plain letter "C", the consonant Half-Rotor
translates the "C" into "R" (the consonant 13 [in
fact the 14th])

After the encipherment, the interrupter advances
of one step and consequently, the two other wheels
advance too (of one step).

Interrupter wheel: 4, V. wheel: 4, C. wheel: 4

Plain letter "C", the consonant Half-Rotor
translates the "H" into "S" (the consonant 14

[in fact the 15th])

A second example with a plugboard setting which
respects the separation between vowels and
consonants.

Plugboard: OEIYAU - DBPZGFRXTWCJNHLVSMKQ

All the other settings are identical to the
previous example.

The word EACH is encrypted in IAMM

A third example with a plugboard setting which
doesn’t respect the separation between vowels and
consonants. In addition we use reverse mode and
decryption mode.

Plugboard: TBZJNR - SKYMPIHLDVWAOFQCXUEG

The word EACH is encrypted in OPCL

Cryptogram:

-----------------

YJDIW WQOLA MBJVA IBJAS FUPEQ ARUTU WGMPU
FMOKV YHOMT DAMZE DYZDP UGUTU SQIMJ ECEBA
FWICK YNBEL AFMDI JFHVU RJAMQ JYZEG BSPHI
HPELV CHAHG QYALH BVOLJ UVYJG YDNUI RBFQA
WCNIT DOXED ULZST YRKYF DKJTG AHGFR FYFCL
XOQHU SROHH LBTYT PKPUM YSGKE SYFHV AQCBU
JVOGY BCSHU RCPBG OGQLI KMYSG OWIVL MYRPE
BNAZH DESUL LTPIP T

Key setting:

Plugboard: IOYAUELPWBZFSHDXGNMJQTVKCR

The sixes : IOYAUE (AEIOUY)

The twenties: LPWBZFSHDXGNMJQTVKCR
(BCDFGHJKLMNPQRSTVWXYZ)

Pins: 00100100001

Direct Mode

Cipher Mode

The interrupter wheel position (from 1 to 47) : 20

The vowel wheel position (from 1 to 6) : 5

The consonant wheel position (from 1 to 20) : 4