The A to Z Challenge asks bloggers to post 26 posts, one for each letter of the English alphabet, in April. Most of us choose to make these posts on a particular theme. My theme for 2022 is Codebreaking in World War II, which fits with the topic of the novel that I’m writing. Visit every day (except Sunday) in April for a new post on my topic.

C is for Cryptography

There are a lot of ‘C’ words in cryptography. Let’s define some.

The definitions in quotes, below, are from the front of a puzzle book called Break the Code: Cryptography for Beginners by Bud Johnson. I purchased it to give me something to practice in after reading Top Secret by Paul B. Janeczko and Code Cracking for Kids by Jean Daigneau. Both of those books had good definitions, too, but I sent them back to the library, long ago.

Cryptography: “The art and science of creating and breaking codes and ciphers.” My old-fashioned print dictionary (Webster’s New Collegiate Dictionary, 1979) tells me that crypto- has a Greek root that means ‘hidden.’ The third syllable ‘-graph’ comes from a Greek word meaning to write. So, cryptography is about secret writing.

Cryptanalysis is obviously related. It’s the word used for the act of studying secret writing for the purpose of decoding or deciphering it. A cryptanalyst is someone who does that work.

In their most precise definitions, codes and ciphers are two different ways of creating secret messages.

Cipher: “each plaintext letter is changed by substituting another letter for it.”

Code book: “A book containing words and / or symbols used in coded messages, together with their actual (plaintext) meaning.”

If you’re doing cryptanalysis, the first step is to determine if you’re dealing with a code or a cipher, because different techniques are used to break them. Of course, the sender can combine codes and ciphers in various ways and, then, you’ll need techniques for both decoding and deciphering if you want to read a secret message.

We often use the word ‘code,’ more broadly to encompass both codes and ciphers. I did that in my title for this series: “The A to Z of Codebreaking in World War II.”

In World War II, cryptanalysts were dealing with something new since World War I – machine-generated ciphers. Here are two non-C words from Break the Code that will help with understanding the significance of that.

Monoalphabetic system: “one letter substitutes for one and only one letter.” The cryptogram puzzles that you find in newspapers and magazines are simple monoalphabetic system ciphers. Obviously, these are too easily broken to be useful in warfare.

Polyalphabetic system: “one letter may stand in place of different letters within the same message.” Machines like Enigma produced polyalphabetic ciphered messages that were very difficult to break. More on Enigma when we get to the letter ‘E.’

I’m going to share two more definitions, because I’m going to use the second one in tomorrow’s post about Agnes Meyer Driscoll.

Substitution cipher: “A code that exchanges one plaintext letter for another.”

Transposition cipher: “A code that changes the order or sequence of letters in the plaintext message.” One of the simplest forms of a transposition cipher is to simply write the message backwards, like this:

Z ot A gniyojne era uoy epoh I