How to Encrypt a Number Shift Cipher
Write down your PLAINTEXT message on a piece of paper.
Create a 5x5 grid, also known as a Polybius Grid, on your paper.
Make sure your grid has 25 squares when you are finished.
Write the numbers 1 thru 5 down the left side of the grid and across the top of the grid as well.
Beginning with the letter A, fill in the squares with the letters of the alphabet. Because there are only 25 squares, cryptanalysts usually put the letters Y and Z together in the last square.
Begin encrypting your message by locating the first letter of your plaintext message in the grid.
Write down the row number followed by the column number.
In our example, the T will be encrypted as the number 45.
Continue until your entire message has been encrypted.
To make your message more secure, leave out the spaces between each word.
CONGRATULATIONS! You have created a Number Shift Cipher!
How to Decrypt a Number Shift Cipher
Based on the KEY provided by the sender, create a 5x5 grid (Polybius Grid). Label the rows 1 thru 5 down the left side of the grid and the columns 1 thru 5 across the top.
Once you have created the grid, fill in the squares with the letters of the alphabet. Because there are only 25 squares and 26 letters, remember to put Y and Z in the same square at the bottom of the grid.
To begin decrypting the ciphertext, take the first number from the message and examine the number's two digits. The first digit is the row number and the second digit is the column number.
Write the letter that appears at the intersection of the specific row and column on the grid.
Continue decrypting the ciphertext until your message is revealed.
CONGRATULATIONS! You have learned how to decrypt a Number Shift Cipher!