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

1

B

2

C

3

D

4

E

5

F

6

G

7

H

8

I

9

J

10

K

11

L

12

M

13

N

14

O

15

P

16

Q

17

R

18

S

19

T

20

U

21

V

22

W

23

X

24

Y

25

Z

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.