Saturday, 5 July 2014

Code talkers

Navaho code talkers

On 4th June this year, Chester Nez (93) died. He was the last of the Navaho code talkers.

In all the reading I've done on cryptography, codes, and ciphers, the story of the American Indian code talkers is my favourite.

Before we delve into their fascinating story, I need to be explain the difference between a code and a cipher.

Codes

A code is a mapping of a word, a short phrase, or even a whole sentence, to a single collection of symbols (words, numbers, or other symbols). They are almost impossible to break through analysis. However, unless it's a very brief code (which can be memorised), a code requires a codebook. There is simply no way to remember all of the substitutions accurately (unless you have a photographic memory!). The existence of this codebook is a security hazard, though. If the enemy gets a copy, you've had it.

Some examples of codes are:

@! = the contract has been signed
pancake = come at once, bring syrup
169 = the plan is proceeding as set
whittle = all is lost, flee!

Ciphers

A cipher operates on individual symbols. It is an algorithm, and once the algorithm has been set, there is no need for a codebook, which is definitely a plus. But they are more prone to being cracked.

The simplest ciphers are substitution ciphers. A=1, B=2, C=3, or even A=?, B=%, C=@. This sort of cipher is easy to crack using letter frequency analysis — the knowledge that in English, E is the most common letter, THE and AND and the most common 3-letter words, and so on. These ciphers are the base of most cryptogram puzzles.

More complex ciphers have been developed, naturally, with all sorts of horrendously complicated tricks and turns. There is a whole cryptography field, after all. But in essence, a cipher is potentially crackable.

Diagram of the SIGABA machine
SIGABA machine
The machine ciphers of the World War II were particularly difficult to crack, but with luck and the incredible skill of code breakers, it did happen. The German Enigma machines were just one type of many. The complex British Typex and American SIGABA cipher machines remained unbroken throughout the war.

Code talkers

Transmitting secure military messages during wartime, without the other side listening in, was (and still is) a major concern.

Native American languages were impenetrable to outsiders, as they had no Asian or European connections. This feature was turned into a 'codebook-free' code by the military. The invisible codebook resided in the Native Americans' native tongues. Code talking was pioneered by a handful of Cherokee and Choctaw Indians during WWI.

Many Indian tribes were recruited during both world wars — six tribal groups in WWI and 13 in WWII. The Navahos in WWII were by far the biggest group, with around 420 code talkers. The Navaho were preferred partially because no German students had infiltrated their culture after WWI, under the guise of studying their culture (as they had done with many other Indian tribes) – and therefore no outsiders had knowledge of their language.

The code talkers needed to memorise quite a lot of code words, but they would only need to memorise that A = Ant, Battleship = Whale, September = Half, and so on — because the hardest part, translating each of the code words into their native tongue, was second nature for them!

1942 letter about code talkers
Before trusting American military secrets to the Navaho code talkers, they were trialled through Navy Intelligence, to see if the top American code breakers could decipher any of the messages. They reported that the Navaho language was 'a weird succession of gutteral, nasal, tongue-twisting sounds ... we couldn't even transcribe it, much less crack it.' (The Code Book, Singh, pg 196) 

An alphabet was developed, from A for Ant in Navaho (WOL-LA-CHEE), to Z for Zinc (BESH-DO-TLIZ). There were up to three variations for the commonly used letters too — so Oil, Onion and Owl all encoded the letter O. This was instituted to stop the Japanese from being able to use frequency analysis if they realised some words were being spelt out. By cycling through variations on these common letters, any frequency analysis would be foiled.

Plenty of the words had direct translation into Navaho — so the English word 'dawn' was translated directly into the Navaho word for 'dawn' (HA-YELI-KAHN).  

However, many terms didn't have equivalences in Navaho. To save time in spelling each word out,  memorable phrases in Navaho were used instead:
Cemetery = among devils (JISH-CHA)
Tank destroyer = tortoise killer (CHAY-DA-GAHI-NAIL-TSAIDI)
Subordinate = helping each other (AL-KHI-NAL-DZL)
Farm = fox arm (MAI-BE-HE-AHGAN)
Dispatch = dog is patch (LA-CHAI-EN-SEIS-BE-JAY)

There were special names for all the various military craft and personnel.
Dive Bomber = Chicken Hawk (GINI)
Battleship = Whale (LO-TSO)
Colonel = Silver Eagle (ATSAH-BESH-LE-GAI)

And countries:
Japan = Slant Eye BEH-NA-ALI-TSOSIE
Australia = Rolled Hat (after the hats worn by our Diggers) (CHA-YES-DESI)

While their radio messages were intercepted by the enemy, they were never deciphered. A great rarity! "Lieutenant General Seizo Arisue, the Japanese chief of intelligence, admitted that, although they had broken the American Air Force code, they had failed to make any impact on the Navaho code." (The Code Book, Singh, pg 201)

You can see the full list of the code talker's dictionary here — information the Japanese and Germans would have literally killed for once upon a time! And this video is just one of many that tells more of their story:


There is a great discussion about Navaho code talkers in The Code Book by Simon Singh, if you want to discover more, and learn more about cryptography in general. There are also several books dedicated to the subject, including Chester Nez's personal account.


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