Like most kids, I was fascinated by secret messages. No, I didn’t have a secret decoder ring–I guess my parents bought the wrong kind of cereal–but I spent hours writing things out in code and trying to write with lemon juice (the original invisible ink). The trouble was, I never had anybody to send a secret message to.
There are many, however, who do have people to send secret messages to–especially military and political leaders. They’ve always been the driving force behind codes. We know that many ancient societies had methods of secret communication; one that I played with as a kid was used by the Spartans around 400 BC. The “scytale” was a cylindrical rod around which the sender wrapped a length of parchment or papyrus in a spiral. The message was written length-wise along the rod, one letter on each revolution of the strip. If the strip was then unwound, the message disintegrated into a meaningless list of characters. The only way to reassemble it was to wrap it around another cylinder of exactly the same size as the one it was created on.
Julius Caesar, when he had a message to send, would write his message normally first, then, underneath it, write it again, shifting each letter three places in the alphabet. So, A became D, B became E, and so on. The Latin word OMNIA, for instance, would appear as RPQLD.
The science of secret messages is called cryptology, which comes from the Greek “kryptos” (hidden) and “logos” (word). It can be further divided into two fields, cryptography, the writing of secret messages (cryptograms), and cryptanalysis, the deciphering of them.
The importance of cryptology is never clearer than during wartime–and the Second World War saw probably the greatest feat of cryptanalysis ever: the cracking by the Allies of the German Enigma codes.
“Enigma” was a machine that could turn plain German into gobbledygook and back again. Essentially it was just a very complex variation on Caesar’s shifted-letter code.
Enigma was invented and patented in 1919 in Holland, and developed and marketed in the early 20s by a German. Anyone could buy it, and in 1926 the German navy began to use an improved version of the machine to code its messages; the army, Luftwaffe and security forces soon followed suit. Enigma did an admirable job of coding messages, and to further complicate matters, each machine included a number of manually adjustable parts that changed how the message was garbled. In peace time the Germans adjusted these parts every month; later they did it every day, and from September 1942 onward they changed them every eight hours. Other parts changed automatically minute by minute. Finally, each message had its own, randomly selected key.
Despite these complications, the Polish secret service was able to read Enigma traffic in the 1930s, having gotten their hands on both an Enigma and an early modified version. Just before Poland was overrun in 1939, the Poles passed on what they knew about Enigma to their new allies, the French and the English..
The English set up an Enigma-cracking unit at the Government Code and Cypher School at Bletchley Park. In 1939 120 people worked there; by 1944 there were nearly 7,000.
The Poles had invented something they called a “Bomba” (because it ticked), essentially a collection of several commercial Enigma machines that together simulated the workings of a German Enigma. Based on that, the Bletchley Park crew created ever-more-complicated machines to help them crack German codes. By the end of the war, that led to the world’s first operational electronic computer, MOSAIC. During the winter of 1940-41, only a few hundred messages a week were being decrypted; by the end of 1942, 4,000 messages a day were being deciphered, a level that remained constant until the end of the war.
This information, code-named “Ultra,” was of huge benefit to the Allies. Some historians estimate it shortened the war by two to three years. Just one example: the entire D-Day operation was planned around the fact the Allies knew from Ultra the number and whereabouts of most of the German Army’s armored divisions and other mobile formations.
Today, anyone can get a cryptography program for a home computer that can create messages Bletchley Park couldn’t have cracked in a century. But of course those who want to read secret messages have computers just as powerful on their side. The security of both individuals and countries depends even more on powerful codes–and powerful code-breakers–today than it did during the war.
Where’s that secret decoder ring when you really need it?
