Encryption Worksheet


Name: _________________________________




Caesar Cipher

Caesar Cipher Encoder/Decoder Chart for k = 3

                    1 2 3 4 . . . 
Plaintext  letters: 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
Ciphertext letters: Y Z A B C D E F G H I J K L M N O P Q R S T U V W X      

To encode:
 
1. For each letter in the plain text, replace it with the one below it 
   in the chart. 

To decode: 
2. For each letter in the cipher text, replace it with the one above it
   in the chart. 

To create a chart for a particular key: 

1. Write the alphabet down and label it "Plaintext letters" 
2. Choose a key between 1 and 26
3. Write A beneath the key-th letter of the alphabet.  Keep writing the alphabet, with one letter below each plain text letter.  
4. When you get to Z in the plaintext alphabet, go back to A and keep going.   

Exercises: 

1. Encode " using the chart above (k=3). 

2. Decode "UF KYV IFTBRNRP" using a new chart for k=10 that you make. 

3. Why is 1 a bad key to use?  

*4. What is the largest number of tries it would take to break a Caesar cipher
   if you didn't know what the key was?