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The secret to encryption

Ewandro Magalhães

Ewandro Magalhães is a conference interpreter, former chief interpreter in the United Nations system, interpreter trainer, and language technology advocate.
He is a TEDx speaker and the author of three books, including The Language Game.

Ewandro Magalhães

Ewandro Magalhães is a conference interpreter, former chief interpreter in the United Nations system, interpreter trainer, and language technology advocate.
He is a TEDx speaker and the author of three books, including The Language Game.

Growing up, I sometimes witnessed my mom speak a totally unintelligible language. It was a funny dialect that mixed random Portuguese words with a few made-up terms chosen primarily for their sound. That lingo was used only when addressing my father, with the purpose of alienating anyone else from the conversation including us, the kids. 

Mom did most of the talking. Dad would typically reply with monosyllables, mostly to acquiesce and signal that the message had been received. Smart man, my dad.

Mom was a code talker. She took a common language and twisted it in such a way as to not make sense. Which is precisely the point in encryption: combining well-known symbols into ciphers according to a logic or key shared only by the authorized parties to a conversation.

In its classic forms, ciphers swap certain letters of the alphabet or substitute them with numbers, using an agreed-upon key. 

For decades in Brazil, back when love letters were a thing, the name “Juiz de Fora” — which designates a city about 100 miles from Rio de Janeiro — became a convenient key for young maidens planning an escapade with prince charming. It provided a string of 10 non-repeating letters that could easily be substituted with numeric digits. It made it possible to share in 

writing some explosive news like 

4b1l41V149mp71Gn9Nt!

Give honey the key,

and the ciphertext can be decrypted into plaintext: 

“I believe I am pregnant!”

 Classic substitution ciphers are easy to crack, though, especially if the key is not long enough. If the correspondence is intercepted, it won’t take long for the father to realize he will soon become a grandfather. He just needs to put in the time.

To be extra safe, Romeo and Juliette could resort to the so-called rail fence cipher, where the plaintext is written diagonally downwards and upwards over an agreed number of “rails” or lines, with the ciphertext read off in rows. 

On a three-rail fence cipher, the message above can be encoded without the help of numbers, as follows

IIIRA  BLEEAPENN  EVMGT or, in plaintext: 

Same plaintext as before: “I believe I am pregnant!”

At this point, they could complicate it further using polyalphabetic substitution mixed with other transposition techniques, but any such pen-and-paper ciphers will eventually be decoded. Their secret will eventually be revealed if a massive number of cracking attempts is made. This is an approach known in hacking circles as “brute force.” 

In time, with more at stake than romance and with love replacing hate, hardware was introduced that increased the complexity of ciphers. In the 20th century, with the world often at war, rotor machines were developed as a means to share strategic military instructions under the radar, protect troops, deploy ships, orchestrate bombings, and plant moles in the enemy’s backyard. 

The Japanese introduced the Purple machine to encrypt diplomatic messages. The Germans bet their chips on the Enigma. 

Originally developed in Poland, the Enigma machine was a clunky electromechanical contraption of rotors and backlit keys. It relied on several disks and plugboards to daisy-chain different and complex polyalphabetic substitutions. Settings were changed daily. 

It was, by 20th century standards, a high-tech solution thought to be unbreakable, and as such it was used to encipher top-secret messages across the Third Reich. 

Yet, it was broken, first by a group of Polish mathematicians led by Marian Rejewski and later by mathematical prodigy Alan Turing and colleagues in the Ultra counterintelligence effort conducted by the British in Bletchley Park.

Turing built his own machine, the Bombe, which looked for patterns in the position of the Enigma rotors and had a computational speed many times faster than the fastest human mind. However, with the Enigma keys being reprogrammed every day, Turing’s team had to start from scratch every 24 hours, with an insane amount and brain power and hard work going to waste once that time elapsed. 

That all changed when Turing and the Bletchley Park crew realized that certain words and phrases were probably used repetitively in German communications. The Germans often started their messages with the same phrase, such as “Heil Hitler” or “An die Front.” They also included a weather report with every message, which often applied the same words to describe recurrent types of weather. 

These repetitive terms, known as “cribs,” drastically reduced the search universe. Once a match was found, codebreakers used the rotor positions to determine the encryption settings and decrypt in full all messages sent that day. 

The story was romanticized by Hollywood in The Imitation Game, starring Benedict Cumberbatch as Turing. In the movie, the crib epiphany is triggered by a casual barroom conversation in which a young lady tries to convince a socially awkward Turing that she could infer the name of a German telegraph operator’s girlfriend thanks to a few give-away repetitions. 

Love wins again. 

On the other side of the spectrum, the Allies, led by the United States,  came up with their own encryption machine. More effective than the Enigma, and virtually impossible to crack, the SAGABA was sadly too bulky and complex to operate, often leading codebreakers into error even when the right key was provided. It was simply not fit for field operations. 

The Allies continued to have their messages intercepted by the Japanese, which put their troops at risk. Their hardware efforts were leading nowhere. Then somebody had a low-tech idea: using a sophisticated yet little known language native only to America.

On that hunch, the US army enlisted 29 native Americans in the US Marines with a mission: to develop a cipher based on the Navajo language that the Allies could use to exchange secret tactical messages through military telephone or radio communications.

Navajo was picked for a few reasons, chiefly among which is the fact that it is a language of limited diffusion, rarely, if at all, spoken beyond the Navajo circles. Secondly, it is a language for which only rudimentary written records existed at the time. Lastly, mastery of Navajo was not enough to decipher the messages. Only those soldiers knowledgeable in the specific code could do so.

This approach was not new. It had been tried with Cherokee, Choctaw, and other native American languages during WWI. Basque would later be used in the 1950s, in a military operation in the Philippines.

The Navajo code talkers, as they came to be known, were trained to use a code that consisted of over 400 terms, including words for military equipment, tactics, and positions. These words were translated into Navajo and given code words. For example, the word “tank” was translated as “tortoise,” and “bomber” became “chicken hawk.” Once encrypted, the messages could be safely transmitted by radio.

The speed and accuracy of the Navajo code talkers was impressive. They were able to encrypt, transmit, and decrypt messages in just a few minutes, outperforming any other encryption system in use at the time.

The Native American code talkers played a critical role in the outcome of World War II. They were used in every major operation in the Pacific, including the Battle of Iwo Jima, and their contributions saved countless lives. The US military kept the Navajo code a secret until 1968. 

Today, the Navajo code talkers are honored as war heroes, and their contributions to the war effort are remembered as an important part of American history. Chester Nez, the last of the original Navajo code talkers, passed away in 2014 at the age of 93. He died a proud Marine. The Navajo cipher system he helped develop in 1942 was never broken. 

For the record, neither was my mom’s.

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