Video Scrambling or video Encryption is an extremely useful method for the stopping unwanted interception and viewing of any transmitted video or other information, for example from a law enforcement video surveillance being relayed back to a central viewing centre.Video scrambling is the easy part. It is the un-encryption that's hard. There are several techniques of video scrambling. However, the human eye is very good at spotting distortions in pictures due to poor video decoding or poor choice of video scrambling hardware. Therefore, it is very important to choose the right video scrambling hardware or else your video transmissions may be un-secure or your decoded video may not be watchable.Some of the more popular techniques for Video Scrambling are detailed below :
Scrambling Method: Whole or parts of the
signal scan lines are inverted.
Advantages: Simple, cheap video scrambling.
Disadvantages: Poor video decrypting quality, low obscurity, low security.
Scrambling Method: Hide/remove
the horizontal/vertical line syncs.
Advantages: Provides a low cost solution to Encryption and provides good quality video decoding.
Disadvantages: This method is incompatible with some distribution equipment. Obscurity (i.e. how easy it is to visually decipher the image) is dependant on video content.
Scrambling Method: Each signal
line is re-ordered on the screen.
Advantages: Provides a compatible video signal, a reasonable amount of obscurity, good decode quality.
Disadvantages: Requires a lot of digital storage space. There are potential issues with video stability. Less secure than the cut and rotate encyption method (see below)
Scrambling Method: Each scan
line is cut into pieces and re-assembled in a different order.
Advantages: Provides a compatible video signal, gives an excellent amount of obscurity, as well as good decode quality and stability.
Disadvantages: Can have complex timing control and requires specialised scambling equipmentThe cut and rotate video scrambling method is probably the best way of achieving reliable and good quality video encyption, an example of a good implementation of this system is in the Obscura-2 video scrambling system
The video scrambling hardware, in particular the decoder should function correctly even if there is a noisy (for example having what are commonly known as 'snow' on the screen. 'Snow' is when there are flecks on your TV screen, often seen in poor reception areas) or unstable signal. If the link to the encrypted signal should stop working then this should not be a problem. The link between the video encoder and video decoder should be regained and the decryption quickly continued.
The very nature of security camera systems is that they are often outdoors as so must be able to withstand the rigours of the weather. The video scrambling hardware should be stable under or protected from the effects of rain, sunlight, extreme heat and cold. It should not be damaged if there is a power spike in the supply. In these systems the video encoder emits a wireless signal to the video decoder unit before it is viewed, it obviously must be the case that the very act of broadcasting the signal does not effect the video encoding hardware and likewise the video encoding hardware should not effect the radio transmitter.
The most important item is that the video scrambling system should be secure, else why bother? It is amazing how some scrambling methods can easily be cracked. For example certain cable television stations 'encrypt' their channel broadcasts via a relatively uncomplex method, which can easily be decoded using a number of cheap bits of electronics from radio shack. That would obviously be illegal! The cable TV's method of encyption is very crude, they usually just dynamically alter the vertical sync signal so that your TV cannot get a proper lock on it and so it scrolls randomly.
The other extreme is to scramble the transmitted video signal too much so that it is costly both in equipment and time to the video at the receiver. Remember that this is a 'live' video scrambling broadcast followed by a 'live' video decryption display. You can't leave your PC chugging all night on this one. ANY electronics can be copied, given enough money and time, but making this process as hard as possible is of benefit as it at least delays the time when illegal copies will be available.
Finally and most obviously each user must have a unique scrambling key so that other users of the system cannot view the transmitted video by accident or purpose without the key owners knowledge. The total number of possible user keys must be such that it is highly unlikely for someone to guess the correct key.
Everyone has a unique
scrambling key or code.
The video scrambling system
should not try and decode not encrypted video transmissions.
The encrypted signal should
be positively identified by the decoder. The decoder should recognise the
encrypted signal and only attempt to decode when fully validated.
On screen status display
Automatic configuration to any video standard.
By Ovation Systems
Due to continual product development Ovation Systems reserve the right to change specifications without notice. E&OE.