Method for encrypting a line-scanned television signal and encrypting and decrypting apparatus.

摘要

A method for encrypting a line-scanned television signal for example from a television camera (18), each line of the signal having a first period during which video information is present and a second period where no video information is present comprises encrypting said television signal in accordance with an encryption key including a line storage device (14) by varying the durations of at least some of said second periods to both increase and decrease the same in accordance with said encyrption key, the extent of variations in the durations of said second periods being such that over a predetermined period of time the total of increases in said durations equals the total of decreases in said durations.