Cipher Table Guide

The cipher table is designed to help you encode and decode messages using a keyword. This method, known as the Vigenere cipher, offers a step up in security from simple substitution ciphers and can be a useful tool for discreet communication.

The cipher table in your planner is a grid with the alphabet listed across the top row and down the leftmost column. Each cell in the grid contains a letter of the alphabet, and the arrangement follows a specific pattern based on the Vigenere cipher.

How to Use the Cipher Table with a Keyword:

Choose a Keyword: Before you begin, both you and the person you're communicating with need to agree on a secret keyword. This word will be essential for both encoding and decoding your messages.

Encoding your message:

• Write down your plaintext message.
• Write your keyword repeatedly above your message, aligning each letter of the keyword with a letter of your message. If your message is longer than your keyword, simply repeat the keyword until it matches the length of your message.
• For each letter in your message, find the row in the cipher table that corresponds to the letter of the keyword above it.
• Then, find the column in the cipher table that corresponds to the letter of your plaintext message.
• The letter at the intersection of this row and column is the ciphertext letter. Write this letter down to form your encoded message.

Decoding an Encoded Message:

• Write down the encoded message you've received.
• Write the agreed-upon keyword repeatedly above the encoded message, just as the sender did during encoding.
• For each letter in the encoded message, find the row in the cipher table that corresponds to the letter of the keyword above it.
• Locate the ciphertext letter within that row.
• The plaintext letter is the letter at the top of the column where you found the ciphertext letter. Write this letter down to reveal the original message.

Example:

Let's say your keyword is "KEY" and your message is "HELLO".

Encoding:

| Keyword  | K | E | Y | K | E | 

| Plaintext  | H | E | L | L | O | 

• To encode 'H' with 'K', find row 'K' and column 'H' in the table; the result is 'R'.
• To encode 'E' with 'E', find row 'E' and column 'E'; the result is 'I'.
• To encode 'L' with 'Y', find row 'Y' and column 'L'; the result is 'J'.
• To encode 'L' with 'K', find row 'K' and column 'L'; the result is 'V'.
• To encode 'O' with 'E', find row 'E' and column 'O'; the result is 'S'.

| Ciphertext| R | I | J | V | S |

The encoded message is "RIJVS".

Decoding:

To decode "RIJVS" with the keyword "KEY":

• Find row 'K', locate 'R', the column header is 'H'.
• Find row 'E', locate 'I', the column header is 'E'.
• Find row 'Y', locate 'J', the column header is 'L'.
• Find row 'K', locate 'V', the column header is 'L'.
• Find row 'E', locate 'S', the column header is 'O'.

The decoded message is "HELLO".

Important Considerations for the Physical Cipher Table:

• Accuracy: Ensure you are using the correct row and column when encoding and decoding to avoid errors.
• Keyword Secrecy: The security of this method relies entirely on keeping your keyword secret.
• Manual Process: Unlike an app where this process is automated, using the physical cipher table requires careful manual steps.
• Table Layout: Familiarize yourself with the layout of the cipher table in your planner to speed up the process.

The cipher table in your planner offers a way to add a layer of encryption to your written communications using a shared secret keyword. While it requires a manual process, it can be effective for certain levels of security.