Caesar Encryption
The Caesar Cipher is one of the earliest and most basic forms of encryption.
This technique was reportedly used by Julius Caesar to transmit secure
messages to the commanders in his army.
The encryption technique uses a simple substitution pattern to change a
plaintext (original) character to a ciphertext (encrypted) character. The
substitution is performed by using a pre-determined key which represents a
"shift" value.
Demonstration
Enter the value "K" in the Encryption Key box. Now, enter the value "E" in the
Phrase to Enrypt box. Then click on the "Demonstrate Encryption" button to
watch how the encryption process works.
First, the key, highlighted in yellow, is used to identify the column that will be
used in the encryption. Thus, the top row of letters represent the key values.
Next, the plaintext character, highlighted in purple, is used to identify the row
that will be used in the encryption. Thus, the first column of letters represent
plaintext values.
Finally, the intersection of the identified column and row, highlighted in red,
indicates the ciphertext value for the associated key and plaintext character.
In this case, the ciphertext value is "O."
Now try it again, but change to the Phrase to Encrypt to "Hello."
What is the ciphertext for this phrase?
Try some others on your own!!!
Check Encryption
Now it's your turn to encrypt a message.
Enter the value "Q" for the key. Next, enter the word "hospital" as the phrase
to encrypt. Finally, manually encrypt the phrase and enter your result in the
box labeled "The encrypted/decrypted phrase is:"
Click on the "Check Encryption" Box to see if you were correct.
Answer the Following
1. Key = W, Phrase = Rabbit. Enter the encrypted phrase:
2. Key = F, Phrase = Shopping. Enter the encrypted phrase:
Practice
Try some more on your own!!!
Caesar Decryption
To decrypt a Caesar Cipher we follow the exact opposite process. The
column, row, and intersection characters mean the exact same as during
encryption. The top row of letters are the possible encryption keys, the first
column of letters are still the plaintext, and the intersection of the row and
column still represent the ciphertext. Instead of going from plaintext to
ciphertext, as is done with encryption, we are going to go from ciphertext to
plaintext.
Demonstration
Enter the value "S" in the Encryption Key box. Now, enter the value "M" in the
Phrase to Decrypt box. Then click on the "Demonstrate Decryption" button to
watch how the encryption process works.
First, the key, highlighted in yellow, is used to identify the column that will be
used in the encryption. Thus, the top row of letters represent the key values.
Next, the ciphertext character, highlighted in purple, is used to identify the row
that will be used in the decryption. Notice that we look for the ciphertext letter
in the column corresponding to the key, not in the first column as was done
during encryption.
Finally, follow the row containing the ciphertext character to find the plaintext
value which is located in the first column. This character is highlighted in red.
In this case, the plaintext value is "U."
Now try it again, but change to the Phrase to Encrypt to "Hello."
What is the ciphertext for this phrase?
Try some others on your own!!!
Check Decryption
Now it's your turn to decrypt a message.
Enter the value "E" for the key. Next, enter the word "hospital" as the phrase
to encrypt. Finally, manually encrypt the phrase and enter your result in the
box labeled "The encrypted/decrypted phrase is:"
Click on the "Check Encryption" Box to see if you were correct.
Answer the Following
1. Key = W, Phrase = Rabbit. Enter the encrypted phrase:
2. Key = F, Phrase = Shopping. Enter the encrypted phrase:
Practice
Try some more on your own!!!