print add to favorites

Author: Lori Stewart
Categories: Middle School, Math, Science

Who hasn’t dreamt of becoming a secret agent - working on clandestine missions and intercepting secret codes? Here's your child’s chance to work on her code breaking and writing skills while covertly developing her analytical thinking skills, too!

Step 1: Your budding secret agent intercepts the following code:

            QBUN QUM NBY ZCLMN MUNYFFCNY NI ILVCN NBY YULNB?
            NBY GIIH.

Step 2: Ask her if she has any ideas about how to break this code. Have her spend a few minutes working on the code and check her progress. If she broke the code, you really have a future agent on your hands, so skip to step 5!

Step 3: This is an example of a substitution cipher. Each letter of the alphabet has been substituted with a code letter. Substitution ciphers can have random orders and patterns that determine which letter was swapped for which. However, in this case, the alphabet was merely shifted. For example, if the alphabet was shifted 2 letters to the right (which it isn’t in this case), the code letter A would really mean C, code letter B would really mean D, and so on. With this in mind have your code breaker take another stab at solving the puzzle above. Sometimes it helps to work on the short words first since there are only so many common short words in the English language (notice how NBY is repeated several times!).

Step 4: Did she solve it? If not, it’s time to give away the key. A key allows a code to be translated back into its original language. The key to this substitution cipher is that the alphabet has been shifted six places to the right. Have your child write out the alphabet as shown below, then fill in the code letters underneath (the first couple letters have been filled in. It helps visually if a vertical line is placed between each letter). She can then use her key to break the code by finding each code letter on the bottom line and substituting it with the real letter above.

Real:    A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Code:   U V…         A B C…
 
Step 5: Code broken? Well done. Now it is time to each try writing your own substitution cipher. Have your child write the alphabet again and decide (secretly!) on her substitution pattern. Have her fill the code letters under the real alphabet and use her key to write a secret message. You do the same. Swap messages and try breaking them without the key. When you can’t stand it anymore, ask for the key and solve!
 

Advanced Code Breaking: If you have a code whiz on your hands, try writing and solving codes where the word spacing is no longer held intact. For example, group the letters in sets of four, so she can no longer use the short words to help break the code. Much more difficult, isn’t it?