How to Use a Caesar Cipher

The Caesar cipher shifts letters by a set number of places in the alphabet. Here's how it works:

Encrypting a Message

  1. Choose a shift number (e.g., 3).

  2. Write your message. Example: HELLO

  3. Shift each letter forward in the alphabet by the shift number:

    • H → K (shift 3 spaces forward)

    • E → H

    • L → O

    • L → O

    • O → R

  4. Result: KHOOR

Decrypting a Message

  1. Know the shift number used to encrypt.

  2. Write the encoded message. Example: KHOOR

  3. Shift each letter backward in the alphabet by the shift number:

    • K → H (shift 3 spaces backward)

    • H → E

    • O → L

    • O → L

    • R → O

  4. Result: HELLO

How to Use a Vigenère Cipher

The Vigenère cipher uses a keyword to encode or decode a message. Here's how:

Encrypting a Message:

  1. Write your message. Example: HELLO WORLD

  2. Repeat your keyword above the message to match its length:

    KEYWORDKEYW

    HELLO WORLD

  3. Use the Vigenère Table:

    • Find the row for the keyword letter.

    • Find the column for the message letter.

    • The intersection is your encrypted letter. Example: H (row K) = R

  4. Skip spaces and write the result:

    Encrypted: RIODA YRMDA

Decrypt a Message

  1. Write your encoded message. Example: RIODA YRMDA

  2. Repeat your keyword above it:

    KEYWORDKEYW

    RIODA YRMDA

  3. Use the Vigenère Table:

    • Find the row for the keyword letter.

    • Locate the ciphertext letter in that row.

    • The column gives you the original letter. Example: R (row K) = H

  4. Skip spaces to reveal the original message:

    Decrypted: HELLO WORLD