Communications Technology Handbook, 2nd Edition

10 Encryption and decryption

The terms scrambling and encryption tend to be used synonymously (see also Television signal processing and systems, p. 392). In this text, however, the term scrambling will be taken to mean the rearrangement or transposition of the order of the original information, while encryption will imply that the original information (often referred to as plain or clear text) has been replaced by the substitution of an alternative code pattern (known as cypher or encrypted text). Scrambling alone is not considered to be secure, because a study of the signal pattern can lead to the design of a suitable descrambler.

The encryption operation is quite simple if the signal is the binary electronic form. When a second binary sequence ...