A one-to-one function and its inverse can be used to make information secure. The function is used to encrypt a message, and its inverse is used to decrypt the encrypted message. The following numerical values are assigned to each letter of the alphabet:

A B C D E F G H I J K L M

1 2 3 4 5 6 7 8 9 10 11 12 13

N O P Q R S T U V W X Y Z

14 15 16 17 18 19 20 21 22 23 24 25 26

Using the function f(x)=3x-1, the message "HELLO" would be encrypted 23 14 35 35 44 since H corresponds to 8 and f(8)=3(8)-1=23, etc.