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WHAT IS CRYPTOLOGY?
The terms code and cipher are often used interchangeably. But they aren't the same. A code is a system in which a letter, number, symbol, or another word is substituted for an entire word or phrase. A cipher uses a letter, number, or symbol to replace an individual letter, combination of letters, or numbers. Sometimes, the order of the letters is rearranged.
Some codes and ciphers are so complicated that they have survived for hundreds of years and have never been broken. Some are so simple you only need a pencil and paper to encode or encrypt them, and later to decode or decrypt them.
Today there are thousands of codes and ciphers in the world, keeping us safe, making our lives easier, and helping us communicate. Some you might be familiar with, while others you may not even recognize even though you see them often. Others are used behind the scenes, so we don't even think about them or know they exist in the first place. At the heart of it all is cryptology — the study of codes and ciphers. And behind all those codes and ciphers are the people who make and break them.
ASSEMBLE A CRYPTOLOGIST'S KIT
Say you want to start a cryptology club. How about naming it the 4 Cs — the Code and Cipher Champs' Club?
First, you'll need to gather the right code-breaking equipment and decide where to keep your supplies.Cryptologists,the name for people with jobs in cryptology, usually have to keep their work secret. They aren't allowed to talk about it, and they try not to stand out. To follow their example, you should find a good place to carry your cryptology tools that won't attract attention. An old backpack will do the trick. Do you have other ideas?
Here are some things to gather to get started. Can you think of anything else for your Cryptologist's Kit?
* Craft knife
* Small straight pin
* Assorted ziplock plastic bags or pencil case
* Small piece of paper or cardboard
* Folders (with pockets)
* Adhesive labels
* Graph paper
* Plain paper
* Backpack or other container for your "tools"
* Magnifying glass
* Pocket dictionary
* Ruler and other measuring devices
1. Collect loose items such as the pencil, markers, eraser, glue, tape, scissors, craft knife, and small straight pin and arrange them in plastic bags or the pencil case. The pin can be secured by tape to a small piece of paper or cardboard.
2. Mark folders with adhesive labels — BLANK PAPER, CODES AND CIPHER TABLES, or other names — to help you organize your papers. Label another folder SOLVING DIRECTIONS AND CIPHER TOOLS to hold materials used for decoding and deciphering such as a Polybius square (see page 15). You will be adding new items to this kit as you work though the book.
3. Use the notebook to take notes or keep other information you want to record.
4. Use the backpack or other container to store all your equipment: the notebook, folders, bags/pencil case, and larger items such as the magnifying glass, flashlight, calculator, pocket dictionary, and ruler and other measuring devices.
5. Once you've gone through Code Cracking for Kids, you might need to reorganize your kit. You might want folders with other labels like SOLVED MESSAGES or MESSAGES RECEIVED, or whatever makes sense to you as a code and cipher champ.
A Lesson Learned Through Sacrifice
Nathan Hale, a spy for George Washington during the Revolutionary War, became one of the earliest casualties of the fight for independence. The 21-year-old was caught behind enemy lines, waiting to make connections for his escape, and was executed for espionage against the British — for spying on them. According to historical records, he had information hidden in his shoe, including sketches of British fortifications as well as notes about the British troops in the area and their positions. At that time, a formal trial was not needed to convict someone of spying. You may have heard what are believed to be Hale's last words: "I only regret that I have but one life to give for my country."
With the death of young Hale, Washington made it his mission to establish a spy network to carry out the work of those wanting independence from England. The work involved courage, patriotism, and, most important, secrecy.
Washington faced a dilemma. Say you wanted to send a note to a friend. You could write it and give it to your friend when you see him or her, but that might not be for a while. Or you could ask another friend to pass it on to him or her, or arrange to leave it on your friend's desk at school. But what if it contained a message that you didn't want anyone else to read? Maybe you're concerned it might be misplaced. What if the person you asked to deliver the note decides to read it? Or what if someone sees it on your friend's desk and picks it up without your knowledge? Then your message wouldn't be a secret anymore. Someone else would have the information intended only for your friend.
By using a code or a cipher, you could make sure no one would be able to understand what your message reveals, except the one who can decipher it — your friend. What is the difference between your need for a secure code or cipher and Washington's? For him it was literally a matter of life and death. One way he achieved the desired secrecy involved using a secret code.
Early Writing And Ways To Hide It
The history of cryptology and how it developed starts long before George Washington and his Culper Spy Ring. Since ancient times, spying and espionage have been used to win wars and dethrone rulers. In addition to other spying techniques such as double agents, secret meetings, and dead drops, governments around the world often used cryptology to keep information from getting into the enemy's hands. And they used cryptanalysis for exactly the opposite purpose: to break the codes and ciphers of their enemies and determine what they have planned.
Countries often used codes and ciphers to disguise messages. Sometimes, however, they conveyed information without encrypting it — unencrypted messages are known as plaintext messages — but hid the messages so their enemies couldn't find them. This technique is called steganography, which comes from the Greek word steganos, meaning "covered or concealed," and graphein, meaning "writing." The beauty of this technique was its simplicity. However, if a plaintext message was discovered, it did not take any special code skills to read it.
Most methods of steganography were simple. Others were more unusual. The Greek ruler Histiaeus would shave the head of a slave and tattoo the message on his scalp. Of course, the slave was unable to leave to deliver the message until his hair grew back. After the slave delivered the message, a response was sometimes tattooed on his head. Again, the slave had to wait until his hair grew back before delivering the return message to Histiaeus.
Ancient Roman Tablets Found in London
In 2016, two thousand years after being used to keep accounting records, practice handwriting, and order provisions, over 400 Roman tablets were discovered at a London excavation site. They're believed to contain the world's earliest reference to London.
The wooden tablets were originally covered with blackened beeswax, and writing was pressed into the wax with a stylus. A stylus is a tool made of metal, bone, or another hard substance, with a pointed end for cutting or scratching letters and a blunt end to rub out letters and smooth the writing surface for reuse. Eventually, the wax was melted and reapplied. But after constant reuse, repeated layers of cursive writing became embedded into the wood itself.
The wood survived in the Walbrook River because it became buried in mud, which prevented exposure to oxygen. Once excavated, the tablets were kept in water until they were cleaned. Researchers treated them with a waxy substance and then freeze-dried them. Of the 405 tablets discovered, about 80 have been read. According to Dr. Roger Tomlin, a scholar of classical civilizations and an expert in cursive Latin, the process is like solving a puzzle — or like cryptanalysis.
Tomlin said he and his team photographed the tablets "varying the angles of light so as to record the whole of the scratches. Then by looking at the tablet under a microscope with a flexible light-source and using the photographs as a guide to recording what you can see, it should be possible, after a time, to start recognizing letters and even words. I should add that, like modern handwriting, you cannot read letter by letter; you have to read words, which then guarantee letters. But you start by reading individual letters. ... Then, like a cryptanalyst, you must try out many different combinations until you find one that 'works.'" Most interesting is information regarding more than 100 people who lived and worked in London as early as 43 CE, including slaves, freedmen, a judge, and a brewer. The handwriting sample might be evidence of the first school in London. What other secrets the tablets might reveal remains to be seen.
Almost 2,500 years ago, the Spartan warriors of ancient Greece would send messages by covering wooden tablets with wax and then writing messages into the wax. But once, a Spartan exile living in Persia learned that the Persians were planning to invade Greece. He had to get a warning to his people without the invaders intercepting it, so he scraped the wax off a writing tablet, wrote his messages onto the wood beneath it, and then re-covered the tablet with wax. The tablet now appeared to be blank, so nobody suspected there was a message under the wax. The tablet made it to Sparta, where Queen Gorgo figured out how to uncover the message in time for the Spartans to gather their forces and meet the invaders in battle.
Herodotus, a Greek writer called the Father of History, told of a nobleman who hid a sensitive letter inside the belly of a freshly killed rabbit. His messenger set off, posing as a hunter. No one suspected that the dead animal he was carrying held a secret message.
New Ways to Solve Old Ciphers
There are two types of ciphers: substitution ciphers and transposition ciphers. They are exactly what their names imply. A substitution cipher is written by replacing the letters of a plaintext message with symbols, numbers, or other letters. With a transposition cipher, the original plaintext letters are used, but they are rearranged or shifted. A Greek scytale is an example of a transposition cipher.
Now try some simple ciphers. Assign each letter of the alphabet a number from one to 26 (a = 1, b = 2, etc.). To encode the word cipher using substitution, replace the letters with numbers and write 3-9-16-8-5-18. You could just as easily give each letter another number, perhaps by starting with 26 and counting backward. Then the cipher would be 24-18-11-19-22-9. You could also give each letter a symbol or even make up your own designs for them. As long as the person receiving the messages has the key — information on what the symbols stand for — you will be able to communicate.
With a transposition cipher, you change the position of the letters but still write in plaintext. For the sentence Meet me at the library, you could write it backward as the single line YRARBILEHTTAEMTEEM. Or you could transpose each word individually as TEEM EM TA EHT YRARBIL. To add a twist, group the letters in a three-or two-letter pattern, such as TEE MEM TAE HTY RAR BIL or TE EM EM TA EH TY RA RB IL. These are examples of making a simple cipher more challenging.
One advantage of a transposition cipher is that it is not subject to a method of deciphering called frequency analysis. It involves just what its name implies: analyzing the frequency with which certain letters appear in an encrypted message to help cryptanalysts uncover a secret message. By determining how often ciphertext letters, numbers, or symbols are used, and comparing those to the most commonly used letters in natural language, you can determine which plaintext letters most likely would fit into an encrypted message.
Make A Greek Scytale
Another unique example of steganography is a Greek scytale (pronounced SKIT-a-lee), one of the earliest military encryption methods. A strip of parchment or leather was wrapped in a spiral fashion around a baton or rod. The sender wrote the message in rows across the strip. The receiver of the message wrapped the parchment around anidenticalbaton or rod to read the message. Some messengers wore the leather strip as a belt to make the message even less obvious.
* 8½-by-11-inch blank sheet of paper, unlined
* Pen or pencil
* 2 additional pencils (identical in size)
* Glue or glue stick
* Transparent tape
1. Cut out two or three ½-by-11-inch strips from the sheet of paper.
2. Hold one edge of a paper strip at a slight angle on one end of one pencil.
3. Carefully wind the paper strip around the pencil, continuing at an angle, overlapping slightly to hold the paper in place.
4. For a longer message, unwind some of your paper strip and glue another strip to the end. Wind the combined strips around the pencil as in step 3.
5. When you have covered the pencil, cut off any excess paper and use a small piece of tape to hold the end in place. This tape will be removed later.
6. Write a message in a continuous row, one letter at a time, along one flat "side" or edge of the pencil. If needed, rotate the pencil slightly to continue writing your message until you are done.
7. Carefully remove the piece of tape. Unwind your paper.
8. This paper is the secret message that you share with a friend. To discover the message, have your friend rewind the paper strip on his or her own pencil, adjusting the angle of the strip as needed so the letters align.
9. To make it harder for others to read new messages, use different cylinder-shaped items for the rods, such as toilet paper, plastic wrap, or wax paper rolls; cans of vegetables or soup; or other objects. As long as you and your friend have identical items for the rods, you will be able to write and read messages.
10. Add the cylinders and scytales to your Cryptologist's Kit for future use.
This technique is effective because certain letters in certain languages tend to be used most often. For example, in the Latin or English alphabet, the letter e is the most frequently used letter, followed by t, a, and o. Less frequently used are q, x, and z. The most common digraph, or two-letter combination that makes one sound, is th. The Spanish alphabet contains the same letters as the English alphabet, with the addition of some accented letters. In Spanish, the most frequently used letters, in order, are e, a, and o. The French alphabet also uses the same letters as the English alphabet, as well as accented ones. The most frequently used letters in the French alphabet, in order, are e, a, and s.
In spite of the usefulness of frequency analysis, it doesn't always work. Say, for instance, you wrote a plaintext message that did not contain the letter e, the most frequently used letter in both English and French. This happened in 1969 when French writer Georges Perec wrote a 200-page novel without any words containing the letter e. If Perec had written his novel in ciphertext, imagine the challenge for cryptanalysts!
Another twist that can challenge a user of frequency analysis is a sentence such as Will we yell wildly when we watch the Wildcats or will we wail in woe when they get walloped? As you can see, it isn't the lack of a common letter that throws off the use of frequency analysis, but the overuse of an uncommon one.
Another way to thwart frequency analysis is to use a code instead of a cipher. Because coded symbols stand in for whole words and phrases instead of individual letters, it's impossible to crack them by looking for frequently used letters. But to communicate via code, both parties must have a code-book that shows how each word and phrase is encoded. Such books can be quite long and cumbersome compared to a cipher key.(Continues…)
Excerpted from "Code Cracking for Kids"
Copyright © 2020 Jean Daigneau.
Excerpted by permission of Chicago Review Press Incorporated.
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Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
Table of Contents
1 WHAT IS CRYPTOLOGY?,
Assemble a Cryptologist's Kit,
Make a Greek Scytale,
Use a Frequency Analysis Chart,
2 CODES AND CIPHERS TAKE THEIR PLACE IN HISTORY,
Write a Message in Hieroglyphics,
Make an Alberti Cipher Disk,
3 COLONIES UNITED,
Make and Write with Invisible Ink,
Make a Jefferson Cipher Wheel,
4 STATES DIVIDED,
Hide a Ciphered Message Inside an Egg,
Create a Message Using a Dictionary Cipher,
5 THE WORLD GOES TO WAR,
Learn the Sounds of Morse Code,
6 BREAKING THE UNBREAKABLE,
Make a St. Cyr Slide Cipher,
Learn to Use the Vietnam Prisoner of War Tap Code,
Create Your Own Flags and Learn and Use Semaphore,
7 HIDDEN ... RIGHT BEFORE YOUR EYES ... AND EARS,
Check the Check Digit,
Help Visitors Navigate Your School,
Be Aware and Be Prepared: Make an Emergency Plan for Your Family,
8 NO ANSWERS IN SIGHT,
Same Tool, Different Results,
Create a Beale Cipher,
9 CODES AND CIPHERS IN A CHANGING WORLD,
Make a Secret Book Compartment,
10 BE A CODE AND CIPHER CHAMP,
Make a Cardano Grille,
Put Your Skills to the Test,
Websites and Places to Visit,