Sending Secret Messages Using a One Time Pad

In this lesson, we will teach you to create secret messages via the way spies did during the cold war.

Required materials:

-Paper

-Pen

-Your mind

(The picture shows the whole process layed out. Don’t worry about that right now)

(At any time you can check if you are correct by clicking this: Link)

Step 1: Creating a Visual Aid

Create a letter to number chart with “A” corresponding to “0” and “Z” corresponding to “25” respectively. This will help you throughout the process of the creation of secret messages and decoding. The picture provided is an example of one.

Step 2: Pick a Message You Would Like to Turn Into a Secret Message

Pick a message that you would like to send. It can be anything, but one rule is no spaces can be used (Example: “the dog” = not valid). So put the words together (example: “thedog” = valid).

Step 3: Now Pick a Key That Will "lock" Your Message

Pick a key that you would like to use in order to transform your message into a secret message.

*Important: the key must be the same letter length as your message. For example, if your message is eight letters your key should be eight letters as well. As well as no spaces*

Step 4: Convert the Message and Key to Numbers

Take your message as well as your key and convert them into their corresponding numbers using your number to letter chart. Examples provided in the pictures.

Step 5: Add the Numbers Up

Place the original message that is converted to numbers and line them up in the first row of the grid like format and the key is the second row. Add the numbers together. (Example in picture).

*This is done like you would look at an excel or spreadsheet document. This is for visual ease.

Step 6: Check If Any of the Totals Are Over 26

If there is a total over 26, subtract the number from 26. For example, if a total of 40 is obtained, you will subtract 26 from it.

Example: 40-26=14

Step 7: Now Convert to the Secret Message

With your secret message in numbers, you will convert the final numbers back to the corresponding letters to reveal the secret message using the letter to number chart. (example in pictures)

Step 8: How to Decode

The following steps show the decoding process.

You will need:

- The key

- The secret message

- The letter to number chart

Step 9: Convert Secret Message and Key to Numbers

To decode a secret message, first you will convert the secret message into the corresponding numbers. You will do the same thing with your key as well. You can convert the letters to numbers using the letter to number chart.

Step 10: Subtract the Numbers

In this step we will reverse the process from encoding which was done by addition. Thus we will need to subtract the numbers. So place the secret message numbers in the first row of the grid with the key numbers in the row below them. Subtract the numbers. Example provided in photo.

*Note that this is done using the spreadsheet method for visual ease*

Step 11: Check If You Have Negative Numbers As Results

If the answer is a negative number, you will then take that number and add it to 26. For example, if you receive an answer of -16, you will add 26 to it. Example: if answer = -16 : (-16) + 26 = 10

Example provided in picture.

If no results are negative, then proceed to the next step.

Step 12: Convert the Resulting Numbers Back to Letters

With your message in numbers, you will convert those numbers back to the corresponding letter with the letter to number chart to reveal what message was being sent originally.

Example provided above.