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Are you familiar with the ideas behind the Caesar cipher but want to learn a little more about it? Have you wondered where the Caesar cipher is used in modern day? As a big fan of the Caesar cipher, I recognize the use of the cipher has evolved greatly over the past 2,000 years. In the past, it was used to pass secret messages, but now it’s solving steps are so well known, this isn’t practical. In short, you may be wondering: How is the Caesar cipher used today? The Caesar cipher is used today for two main purposes. One is a simple substitution either on a ring, wheel, or other activity to get kids into cryptography. The other way it's used is to hide hints, answers, jokes, etc on various forums and groups to prevent accidental casual reading without being too hard to decrypt. Check out the rest of the article for more information. When Was The Caesar Cipher Used? The Caesar cipher was originally used in 100 B.C. by Julius Caesar. He used the cipher to send messages secretly to his armies. The cipher was simple enough his officers could remember how to encrypt and decrypt messages. It helped that the common soldier of the time was illiterate, and there weren't dedicated studies on cryptology at the time. It’s unclear if Caesar truly invented the shift cipher, but he is the earliest and clearest historical figure we know of to use the cipher extensively. What Was The Caesar Cipher Used For Back Then? We touched on the use of the Caesar cipher above as a means for encoding messages, so the casual reader would have a tougher time figuring out the message. The Caesar cipher is a simple substitution cipher. In essence, each letter is replaced with another with the end result of a jumble of letters. The mechanism for choosing which letters are substituted with which ones is based on a shift in the alphabet. For example, with a shift of 1 or ROT1, every A in your original message is now shown by B (shifted over 1). B becomes C, and C becomes D. In this way, the original message or plaintext is turned into ciphertext. Example: Plaintext: THIS IS A MESSAGE YOU SHOULDN’T READ. Ciphertext (ROT1): UIJT JT B NFTTBHF ZPV TIPVMEO’U SFBE. See how the message is harder to read? But by figuring out which shift used, it’s actually simple to decrypt the Caesar shift without a key. It’s this reason the Caesar shift isn’t considered very secure. There are 25 shifts available, one for each letter. Some people consider A → A a shift (as either 26 or 0 shift), but nothing would change, so it’s impractical in its use. How Is The Caesar Cipher Used Today? Because the Caesar cipher is easily cracked, it’s not as useful today in the encryption or security field. Even more advanced substitution ciphers fall prey to brute force attacks by computers. So where does this leave us with the Caesar cipher? Well, there are two main places you’ll find it in the modern day. Introduction To Cryptograms This is the most common use of the Caesar cipher. Everyone has to start somewhere, and the shift cipher is usually the place to go. When I was a kid, there were special decoder rings hidden in cereal boxes. The ring would have the standard alphabet aligned with different letters of the same alphabet, just shifted over. This is an example of a Caesar cipher. When I was in school, one of my favorite bonus worksheets to do was one called “Secret Message” where you had to use a printed wheel to decode a message. This worksheet often used another example of a Caesar cipher. Even as an adult, when I wanted to get back into cryptograms, the first book I bought started with Caesar ciphers. These are just challenging enough for new cryptologists to enjoy and feel pride when solving the puzzle, but not so hard you get frustrated and quit. When people ask me where to start with cryptograms, I happily point them in this direction. This is also the reason it’s one of my favorite ciphers; as a teacher by day, I know how important it is to give students just enough of a challenge or taste to get them interested without making them feel too frustrated. Hiding Information From The Casual Glance The other practical use for the Caesar cipher is to hide a message from a casual glance. I’ve often looked up challenging questions or riddles in books online, and I get so frustrated when I glance down and accidentally read the answer, hint, or punchline when I don’t want to. Even the ones which put it upside down still are too easy to read. I also dislike having to flip to the back for a clue or to check my answer. It’s extra work! Enciphering the clue, hint, answer, or punchline with a Caesar cipher has become common practice in some books, but especially with certain online communities. The ROT13 is the most common shift used. With a RO13, you’re able to apply the same shift number to encode and decode the information. Mathematically, this is because the number 13 is halfway between 26 (the number of characters in the English alphabet). Other common shift keys include ROT1 and ROT3. Shifts between 1-6 are also used regularly in cryptographic groups to encipher hints. The idea is that these numbers don’t take much effort to decipher, and with practice, many will be able to decipher the text without even pencil and paper help. Final Thoughts Now you know how the Caesar cipher is used today. Though it’s fallen out of favor as a means of keeping information secure, the shift cipher does serve an important purpose in introducing new people to basic cryptography and hiding information you don’t want people to accidentally read at first glance. Hagvy arkg gvzr! ROT13

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