The Red cipher machine

• Introduction (This Page)
• Working
• History
• Genuine messages
• Procedures
• My Simulator
• Cryptanalysis
• SIS's Cryptanalysis
• Challenges

Introduction

The RED machine is a cipher machine used to protect Japanese diplomatic relations between the two world wars.

The RED machine offers very weak cryptographic security. In fact, this is the case for all cipher machines designed between the two world wars, with the notable exception of the military version of the Enigma used by the various German military services before and during World War II.

This machine was broken by most of the major cryptographic services of the time: those of the American Army and Navy, the British, and the Germans. It should be noted that only the French did not break this machine. Yet, France, with its possessions in Indochina potentially threatened by the Japanese, had an interest in deciphering the Red messages. It is true that the cryptographic level of the French cryptographic services had fallen considerably after their mastery during the First World War.

What is the major weakness of this machine? It stems from the stinginess of the Japanese diplomatic services. Diplomatic messages exchanged between the various embassies and the Japanese Ministry of Foreign Affairs circulated on private networks and therefore required payment. The price is reduced if the telegrams are composed of pronounceable words. To achieve this goal, the RED machine encrypts each vowel by a vowel. So the cipher is divided into two parts: the cipherment of the six vowels and the cipherment of the twenty consonants. Although this separation later disappeared, the separation between six letters and twenty letters persisted, even in the Purple machine, which replaced the RED machine. This separation, incomprehensible to any serious cryptologist, jeopardized the Red and Purple cipher machines.

Japanese cipher Machines

The RED machine is one of a whole range of cipher machines created by the Japanese between the two wars. The most recent were used during World War II.

• The Orange machine. It uses Japanese syllables (Kana). It dates back to the early 1930s. It was used for communication between Japanese naval attachés.
• The M2, a machine used by naval attachés and which uses the letters of the alphabet.
• The Red machine is very similar to the Orange machine. It was used by the Foreign Ministry. It uses the letters of the alphabet (Roma-ji).
• The Green machine was inspired by the commercial Enigma machine but used flat rotors (as in the Turing/Welchman Bombe). It apparently saw little use.
• The Purple machine succeeded the Red machine in 1939.
• The Coral machine succeeded the Orange machine for the naval attaché network.
• The Jade machine, similar to the Purple and Coral machines, is used by the Japanese Navy.

The names of the machines

The RED machine has several names. First, Japanese names:

• "Type A Cipher Machine" (Japanese: angoo-ki taipu A). The Purple machine was called "Type B Cipher Machine."
• "Alphabetical Typewriter 91" (Japanese: 91-shiki oo-bun in-ji-ki). The number 91 indicates that it was designed in 1931, which corresponds to the year 2591 in the Japanese calendar. The Purple machine was called "Alphabetical Typewriter 97" (Japanese: 97-kyūnana-shiki ōbun injiki).

But it is also referred to by several American names:

• The name RED was given by the American Army cryptanalysts (SIS). This name RED refers to the color red as it appears in the rainbow. Indeed, the RED machine was the first Japanese cipher machine studied by the SIS. Subsequently, the colors Orange, Green, and Purple were used for subsequent machines.
• The name M-3 (Model-3) was given by the U.S. Navy. The M-1 model, also called IKA, corresponded to the Orange machine (Army). The M-3B machine is called Purple by the Army. The M-3A machine is an improvement of the RED machine dating from 1938 (see History Page).

However, the common name is "RED" because the majority of sources describing this machine, its history, and its cryptanalysis come from the U.S. Army.

History (in brief)

Like many cryptological services, Japanese diplomacy, after the First World War, considered acquiring cipher machines to replace the cumbersome Codes. The Japanese were following the advice of the French General Cartier, who advocated the use of cipher machines.

Based on the cipher machines of the time, notably the Kryha and B-21 machines, the Japanese created the RED machine.

This machine was used in Japanese embassies from 1931 to 1938. From 1938 onward, it was replaced by the Purple machine.

As mentioned above, the security of the RED machine was very weak, reflecting the low level of Japanese cryptological services.

Japanese cryptological services undoubtedly had to interact with each other. Indeed, naval attachés used the Orange machine, similar to the Red machine.

References

Books and Articles

• Battle of Wits - The Complete Story of Codebreaking in World War II, by Stephen Budianski, The Free Press, 2000. In this book we can find a few pages devoted to the Red machine from the point of view of American cryptanalysts.

Internet Links

• Wikipedia - Type A Cipher Machine. This article is very interesting because it features a photo of the Orange machine (similar to the Red machine) and another photo of the American machine that emulated the Red machine.
• NCM - National Cryptologic Museum - You can search by keywords (RED Analog, RED machine, etc.) (link). In addition to numerous photos, you can read the document VF131-002 which describes the different Japanese cipher machines and in particular the M-3A model which corresponds to the evolution of the RED machine.