Code 62 : Navajo Cipher

Navajo Cipher

Background

The Navajo, which are also called Diné, are one of the biggest Indian cultures in the USA. In the beginning of 1942, Philip Johnston started working on a new encoding system. He grew up in a Navajo reservation and thought back to his childhood and the Navajo language, which he spoke fluently. He knew how alien the Navajo language sounds to outsiders because it is not in any way related to any European or Asian language and uses a totally different grammar structure. This knowledge led him to the idea that it might be a good idea to use Navajo people as radio operators. A series of tests followed with the intention to find out whether only the Navajo tribe or other Indian tribes also could be used for this purpose. But since the Navajo tribe was the only one with a sufficiently large number of literate people and the fact that the tribe had not yet been investigated by German researchers, no other tribe was considered as an option.

To test the security of the procedure, a message encoded with the Navajo code was given to the marine reconnaissance team that previously was able to break the "Purple" code, the most advanced Japanese cipher. They were not able to break it.

The application of the Navajo code during the war was considered to be a great success. During one battle, marines were accidentally attacked by an American unit. Radio messages transmitted in English did not stop the attack because the attacking unit considered it to be a Japanese deceit tactic. Finally, after the same message had been transmitted in Navajo, the attack stopped because the Navajo code was considered to be unbreakable.
420 Navajo code speakers were trained in total. Their services were not honored until 1986 because the military insisted on strict nondisclosure about this matter.¹

Principle

Four months after the attack on Pearl Harbor, 29 people from the Navajo tribe joined the Marine Corps. One initial problem was the fact that many modern, technical words were simply non-existent in the Navajo language. Therefore, a Navajo dictionary was created, which includes technical terms for planes, ships and so on. The names for some military vehicles were derived from Navajo words for birds and fishes etc.

This dictionary covered 274 words that the Navajo officers had to learn by memorization so that there were no print copies of the dictionary, which could be stolen by the enemy. Despite these efforts, there were still some words that could not be directly translated. These included for example names and locations. These terms were translated according to such a translation table.

Fig. 1: Navajo-Alphabetcode²

The dictionary was expanded by 234 commonly used words later to make frequency analyses as hard as possible. Aliases for frequently used characters like the "E" were used analogous to homophonic ciphers.¹

Security

The Navajo code is one of few ciphers that was not cracked during the time of its application. But still, the security crucially depended on the nondisclosure of the Navajo language, so if the Japanese had managed to abduct one of the Navajo people, the code could have been rendered useless.

Weblinks

http://en.wikipedia.org/wiki/Navajo_code

References

1	Singh, Simon: "Geheime Botschaften", Carl Hanser Verlag, 1999, P. 237ff
2	Singh, Simon: "Geheime Botschaften", Carl Hanser Verlag, 1999, P. 241