Newnes Radio and RF Engineering Pocket Book, 3rd Edition

12 Information privacy and encryption

12.1 Encryption principles

Radio communication was never secret, but since the advent of fast

frequency scanning receivers the ability to overhear, even on cellular

radio telephones, is within easy reach of anyone. Privacy systems are,

however, available which will deter the casual listener and gain time

against the determined eavesdropper.

Messages, which may be either speech or data, are encrypted to

prevent both eavesdropping and the injection of spurious information.

The aim is to make the encryption and decryption as easy and inex-

pensive as possible for authorized users and time-consuming, difficult

and costly ...