Substitution Ciphers

Caesar’s cryptic messaging with a simple alphabet shift soon became obvious to the least experienced cipher analysts. A fresh approach was needed. Let’s begin to look at the world of  the simple substitution cipher where letters are randomly chosen to depict other letters of the alphabet. Randomly selecting a cipher letter (ciphertext) to represent another letter (plaintext letter) revokes the ease of simply looking for the number of shifts that a letter had been moved.

Simple substitution ciphertext is limited only by the ingenuity and imagination of the constructor (cryptographer). As mentioned in Chapter One, its foundation may lie in an everyday substance found in the home, at work, at play or on the street. A picture, book, dictionary, newspaper, keyboard, or computer internet text may be the basis of ciphertext.

In our computer age of today, we use codes for many every day activities. Your zip code is a simple method of identifying your state, city and street address where you live. Bar codes on labels speed the supermarket checkout line with pricing information. A Personal Identification Number (PIN) allows us to do banking at automated tellers. Our social security number identifies who we are, where we work and reports annual earnings to the Internal Revenue Service. (Perhaps not all codes are pleasantly used.)

Finally, there are thousands of persons like us who construct and decipher codes and puzzles for the everyday enjoyment of it. It provides a relaxing escape from our busy daily activities.

When all the letters in the ciphertext (disguised message) are exactly the same as those in the plaintext (original) message, but simply rearranged, we refer to it as a transposition cipher. The letters are all the same. Only their order has been altered or changed.

When the plaintext is changed to a different letter or symbol, the cipher is called a substitution cipher. The symbols or letters have been substituted for the plaintext. Once a plaintext letter is assigned a ciphertext letter or symbol it must use the same substitution throughout the cipher. (We refer to this as a simple substitution cipher.)

We are going to have some fun in this issue with a substitution cipher with a date back to the middle ages in Europe (500 AD to 1500 AD), also popular in the American Civil War (1861 to 1865). Today it is commonly known as the Pigpen Cipher, most likely because the cipher symbols look like penned areas.

Most important in the communication of cryptography is a KEY set up by the correspondents in advance that determines the steps to be followed in the enciphering (constructing the disguised message) and deciphering (retrieving the original message) processes. The Pigpen Cipher Key might be set up in a grid as shown below.

This shape of the grid would indicate the letter group: 

Indicates the letter “T”:

“Send” would look like this:

Pig Pen Ciphers

An interesting phenomenon has occurred while putting this column together for the reading and ciphering pleasure of the younger generation. There is a young at heart generation out there that has been reaping its own ciphering harvest from these basic fundamentals of cryptography principles. A group, not exactly eligible for the Kiddee Krewe, but somewhat interested in the mysterious, fascinating, and compelling force causing grown persons to eagerly await each issue of the Cm, has been prompted to find out what this cryptography fuss is all about. Welcome aboard. We will try to make the ride a pleasurable one. I invite you to make this column available to all family members. If you have found the first two cipher types we have reviewed to be fun, you will find many more like them in the following books:

You will find many substitution type coding devices described in these books that are found in your own home. The ciphers below have been constructed with the help of the ordinary telephone dial. Each telephone digit can be represented with up to three letters of the alphabet. See if you can build upon the knowledge you have already gained to work on their solutions. (Hint – remember the Pig Pen Cipher.)

Telephone Ciphers