The Red cipher machine

• Introduction (This Page)
• Working
• Genuine messages
• My Simulator
• Cryptanalysis
• Cryptanalysis by Rowlett & Kullback
• Challenges

Introduction

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

The Japanese name for the machine is "Type A Cipher Machine" (Japanese: angoo-ki taipu A). It is also known as "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. 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, which used the code name "RED" to name it.

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 depended on the number of words in the telegram or, in the case of encrypted messages, on the number of groups of five letters. The RED machine was designed (originally) to encrypt vowels and consonants separately. This resulted in pronounceable words, which reduced the cost of transmitting cryptograms. 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.

History

Like many cryptological services, Japanese diplomacy, after the First World War, considered acquiring cipher machines to replace the cumbersome Codes.

Based on the cipher machines of the time, notably the Kryha and B-21 machines, and following the advice of French General Givierge, the Japanese created the Type A (Red) machine.

This machine was used in Japanese embassies from 1931 to 1938. From 1938 onward, it was replaced by the Type B machine (US code name: Purple).

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 (another US code name), similar to the Red machine.

References

Books and Articles

• The Emperor's Codes - The Breaking of Japan's Secret Ciphers by Michael Smith, Penguin Books, 2000. This book gives us the British perspective.
• The Broken Seal by Ladislas Farago, Bantam Books, Inc., 1967. This book gives us the perspective of the U.S. Navy's cryptological service (and thus their results in connection with the Orange machine), including their success following espionage.
• The Story of Magic by Frank B. Rowlett, Aegean Park Press, 1998. This book describes the cryptanalysis of the Red machine by the U.S. military.

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.