Why was the Navajo code not broken by the Japanese in WWII?

Question

In reading about this topic recently, to my understanding, the encryption schemes used on top of the Navajo language were very simple and definitely could have been broken (my research shows they mapped Navajo words to various different meanings).

The Navajo language alone is obscure, had few speakers, and was not a written language - but still I'm amazed that the code was never broken. Isn't this an example of "Security through obscurity"?

No matter how obscure the language was, the sounds still mapped to English phrases at the end of the day. Through cryptanalysis, shouldn't the Japanese have broken the code? Am I missing something here, or is this an example of security through obscurity actually working?

Edit: Follow up question: Could a similar scheme work today?

Answer 1

Wrapping up my comment as an answer:

Imagine you’re a Japanese cryptanalyst in the year 1944. There is no such thing yet called “television”, and you’re still decades away from a wordwide network feeding you with all the knowledge you could wish for.

In that case there’s only a minimal chance you’ve ever heard or seen a Navajo. So, you’ll be wondering what “Joe” is talking about as it sure doesn’t sound like English. You‘ll be asking yourself things like: Is that the plaintext in some language I don’t recognize or simply a failed decryption attempt?

Furthermore, even if you would know it is Navajo and assuming you would have some plaintexts to your availability, you would still be wondering about the more simple things of cryptanalysis, like: What’s the character frequency of Navajo anyway?

Even more, since Navajo is a descriptive language. Even having things like character frequencies and plaintexts at hand, how would you know what is meant by (eg) “wolf feeds bisons when eagle moon embraces cloud rock”?

See, Navajo indians may know “cloud rock” from stories told by their elders and they may know the exact day in the year when the “eagle moon embraces“ it… but you – sitting in your cryptanalysis room in Japan – have a rather minimal chance of even grasping half of it.

All in all, the use of Navajo boils down to a suplemental layer of “security through obscurity”. Maybe it helps if you think of the Navajo communicators as “living codebooks”. Embedding them (especially in key positions) added an additional layer of security to the already used cryptographic protection during radio communication et al.

In fact, take the actively used (radio) encryption during WW2 and add a layer of Navajo language use on top of it, and you’ll end up with something that could almost be called “double encryption”.

edit

To answer the additional question from your comment (now follow-up question added as an edit)…

I think both of these are good explanations of why this scheme worked. From your explanations it seems to me the primary reason it wasn't broken is because it happened 70 years ago. Am I correct in saying this would never work today?

Under most conditions – Yes, that’s correct.

Of course, this depends on the exact situation. The reason I’m saying that is that there aren’t many Navajos living today (last I heard was something in the thousands). Some specific scenarios might change that “yes” to a “no”. But generally, looking at the means (and resources) available today, I tend to say that – in contrast to the WW2 – they indeed wouldn’t be very helpfull in terms of security. Actually, it’s like using the Klingon language from Star Trek, or Elvish from Lord of the Rings… as long as only a few know it, it might add a minimal bit of security. But nowadays, you can even take online courses to learn Klingon, Elvish, etc. Back in 194-something, the situation was quite different.

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_{As an aside: I used the name “Joe” on purpose, since it was a commonly used nickname for US-American soldiers during World War 2. Another example of such a naming would be “Tommy“, which was used to hint at English soldiers.}

Answer 2

The Japanese made efforts and could have broken Navajo code later in the War since Joe Kieyoomia didn't know teaching Navajo would damage the confidence of the code greatly. Even without his help, one doesn't have to know a language before breaking code written in it, as long as one knows its Orthography. Even if no Orthography given, folks still interpreted Cuneiform and Linear B. And even if you cannot interpret it, specific expressions like Apache can be linked to concepts like rasen yokuki🚁 without knowing the intermediate notions like some Indian tribe or a helecopter.

A real world example:

Plain text: Send demolition team to hill 362B.
Code words: SHEEP, EYES, NOSE, DEER, Blow up, TEA, MOUSE, TURKEY, ONION, Sick Horse, 3, 6, 2, BEAR.
Ciphertext: Dibé, anáá’, áchį́į́h, bįįh, ahdeeltahi , dééh, naʼastsʼǫǫsí, tązhii, tł'oh chin, łį́į́ da’atsaah, táá, hastą́ą́, naaki, shash.

Codes compiled in simple substitution like iron fish, bird, turtle, water would offer more than enough simile or metaphorical clues to divulge its meaning. The Japanese would even found more similarities in Navajo grammar with their own mother tongue than the Americans.

The problem was, Navajo Code was a tactic code used by small units with short range radio carrying information which expired quite soon. You had to deploy to the Front linguistics to interpret or Phonetic Alphabet experts to transcribe an unfamiliar language in a different language family in time. The Japanese, nevertheless, just didn't make it.

Or did they?

Some discussions after March 2018:

• Why couldn't Japan crack the Navajo Code in WW2, when they captured a Navajo native speaker?

• Did the Japanese know Navajo code talkers were used in WWII but were unable to crack the language or did they have no clue what language it was?

• How close was Japan to cracking Navajo code talkers? Was Japan aware Americans were using a Native American language as code?

Answer 3

The "descriptive" language aspects certainly adds ambiguity in the word-symbols used, and thus entropy. If a rocket is one time described as "a spear that giants appreciate as a marital aid", the next time as "an opaque bottle filled with what decisively gives things direction", yet another time as "wisps smoke and fire chasing a wisp of steel" or "what lives by an orange fart, and dies by an orange fart" (none of these are Navajo, they are my own twisted ad-hoc inventions) - there is very little similarity in multiple plaintexts that describe the same thing, while descriptions for completely different things would appear very similar when trying to establish a pattern - "a transparent bottle filled with what decisively frees men of direction" is more likely to describe supplies for the officer's mess...

Answer 4

There were only 400 code talkers. In the wider context of a war spanning the pacific with millions of participants, there were bigger fish to fry.