Jessica, Hespeler | June 1, 2021
Have you ever tried to keep a secret? Think about how hard it was. Now imagine if your life, or the lives of others depended on your secret keeping skills? What if you needed to write down your secret and share it, but make sure that your enemies couldn’t read it. How would you do it? History provides the answer: codes and ciphers.
History is filled with groups who have encoded and enciphered their messages to keep them from being understood by opposing groups. There is a small difference between a code and a cipher which is worth noting. Using a code involves replacing words in a message with other words. For example, if you want to tell a colleague that, “the car is in the driveway” you might say, “the package is in the post.” The codewords in this example are package and post.
A cipher on the other hand, replaces each letter of a message. The sender and receiver only need to know the correct substitution to send secure messages, instead of each side memorizing long lists of codewords. One popular substitution cipher is the Caesar Cipher, named after Julius Caesar. In this cipher, each letter of the alphabet is shifted a certain number of spaces. For example, if I shift the alphabet by 9, A becomes j, B becomes k, and so on. “Meet me for lunch” becomes “Vnnc vn oxa udwlq.” The sender and receiver only need to agree on the number of the shift to cipher and decipher messages.
The best code is one that is easy for the sender and receiver to remember, but difficult for an outsider to guess. Too complex a cipher creates the need for code books, outlining the rules of encoding and enciphering, which could easily fall into enemy hands. Too simple, while easy to memorize, is also easy for codebreakers to crack. A Caesar cipher is too easy because a determined codebreaker can try every letter shift, a “brute force” attack, until they find the right one.
What type of code meets this criteria of being complex enough but not too complex? In World War II, Allied forces trained a group of Navajo Code Talkers to use their own language for coded transmissions. The Navajo (or Diné) language was too complex for codebreakers to decode, but both the sender and receivers were fluent in their own tongue and could translate messages easily.
Keeping a code secure, or cracking a code, can have dire consequences. When Mary Queen of Scots plotted the assassination of Queen Elizabeth I, she enciphered her messages. Believing her ciphers were secure, she wrote openly about her plot. Unfortunately for her, the Queen’s spymaster Sir Francis Walsingham cracked her code and presented the evidence at her trial. As a result, she was found guilty and executed. If she had created a more secure cipher, or if Walsingham’s team hadn’t been adept at codebreaking the trial would have played out differently.
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