Viewlock II video encryption Product Description
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Viewlock II Encryption System Product Description


ViewLock Video Encryption Introduction

The Viewlock II video encryption system has been specifically designed to protect microwave surveillance links from interception where sensitive information is being transmitted.

Viewlock II utilises line cut and rotate scrambling, offering a very high level of picture concealment coupled with excellent security. The video encryption has been designed to be very robust and is tolerant to the problems associated with microwave links in marginal reception conditions such as multipath and noise. These features, coupled with its small size and low DC power consumption, make Viewlock II the ideal system for protecting covert security links without a significant loss in range or operability, even in difficult environments.


The encryption system consists of an encoder and decoder housed in small, fully weatherproofed cases, operating from a DC supply of 6 to 32 Volts. Current consumption is less than 55 mA at 12 volts, so the units may be battery operated if required. Viewlock II offers excellent decoded picture quality and incorporates full 8 bit digital processing in both the encoders and decoders and the system exceeds ITC outside broadcast specifications.

Viewlock II incorporates a dedicated chip (ASIC) which as been developed by Ovation Systems to perform all the video encryption encoding / decoding functions in one unit. The use of an ASIC allows the system to be highly integrated improving size, current consumption and security.

Block diagram of the video encryption encoder and decoder
Block Diagram of the video encryption encoder / decoder


The Viewlock II encryption system has been designed so both the encoder and decoder are of the same basic architecture. Indeed, it is possible to configure any Viewlock II unit to be either a video encryption encoder or decoder simply by adjusting an internal DIP switch. Please refer to Figure 1 above showing an outline block diagram of the Viewlock II encryption encoder / decoder.

Dynamic Line Cut and Rotate Scrambling

Video enters the encoder and is digitised using an 8 bit A to D converter. The video is then manipulated in the digital domain to produce a random cut and rotate of each video line. This is achieved by choosing a cut point during the active video line and then presenting the last segment of the line to the output first, followed by the first segment. Proprietary techniques are used to help the system reconstitute the original line information within the decoder that improves the robustness of the scrambling. Viewlock II is able to automatically detect a 625 line or 525 input and configure itself accordingly, without the need of intervention by the user.

The line cut rotate scrambling method has the advantage of keeping all the horizontal and vertical video sync information in its original position whilst completely obscuring the source video. This ensures the encrypted signal is compatible with PAL or NTSC standards, especially important with transmission systems that employ black level clamping.

To ensure the decoder is always operating at its optimum performance, it is able to automatically compensate for up to a +15% variation in video input level, through an AGC system. Even if the video input outside this range, the decoder will still function from levels of 0.5 to 1.5 Vpp, again showing the robustness of the system.

line cut an rotate video scrambling
Line Cut and Rotate Video Scrambling


Encryption Security

Viewlock II uses proprietary algorithms held in a secure microcontroller to manipulate the video lines. The encryption algorithm, seeded by a private key set buried within the microcontroller, produces a random sequence of line cut positions. Viewlock II uses a 32 bit primary key, so there are a minimum of 232 , or over 4.3 billion, possible combinations before a cut sequence is repeated. It is therefore very difficult (impossible) to predict which cut point and sequence will be used next, as there are so many possible combinations. Furthermore, at power up, Viewlock II starts a completely random point within the sequence by generating a random 32 bit word by taking the least significant bit of 32 video samples.

The encoder and decoder are synchronised by an encrypted over-the-air data channel, sent over one of the video’s unused vertical blanking interval (VBI) lines. Both the encoder and decoder must have the same private key sets to allow the system to decode. Key sets are programmed at the factory and may be allocated to single encoder / decoder pairs or to groups of units as required.

To improve the security even further it is possible for the user to download a secondary key (or code set) of 32 bytes held in E2PROM, over the RS232 port. This code set is then used to randomise the cut sequences by a further 2256 possibilities, resulting in a possible 2288 combinations (~ 4.7 * 1086 ). This facility has the advantage of ensuring that even in the unlikely event of a decoder lost or stolen, a fundamental part of the sequence generation can be easily reprogrammed to a new code set, which will only be known by legitimate users.



Encryption Installation and Operation

The Viewlock II video encryption system is very easy to set up and install. Video input and output is via standard BNC connectors, DC power via a professional Lemo connector. The units are fully weatherproofed to IP65 and therefore are suitable for long term outdoor operation if required. The video interface is standard 1 Vpp 75W and system will automatically configure itself for 525 line NTSC or 625 line PAL operation.


The DC power requirement is from 6 to 32 Volts, with a current consumption of around 55 mA at 12 Volts. The current consumption reduces with increasing input voltage as Viewlock II incorporates a DC to DC converter to offer the widest possible DC operating voltage range.


Encyption Installation and Diagram


Vide Encryption Unit
Video Encryption Unit


As standard Viewlock II has an onscreen display which displays "SECURE" when decoding correctly and "INSECURE" when the video is ether clear or not decodable. To aid fault finding, Viewlock will display a "NO VIDEO" message if video is not present at the encoder's input and display "NO LINK" if there is video input to the decoder.

If either the encoder or decoder is unable to process the video, or if the power fails, the video input is bypassed directly to the output. This is achieved by an internal low power relay, so the bypass operation is fail safe. In some situations it is not desirable to transmit video that is not scrambled under any circumstances, in these cases it is possible to disable the bypass function.

Audio Encryption Option

In the same package size, Viewlock II may be upgraded to carry two scrambled audio channels along side the scrambled video. Audiolock II digitises the incoming audio and scrambles the resulting bit stream. The digital audio is then transported from the encoder to the decoder by adding data to unused video lines within the vertical blanking interval, resulting in a very secure audio transmission. Audiolock II may be configured to encrypt one audio channel of 15 kHz bandwidth or two channels of 7.5 kHz. To improve the signal to noise performance of the system, adaptive differential pulse code modulation (ADPCM) is used, providing an excellent S/N specification of > 60 dB (weighted).

Video and Audio Encryption Application Diagram
Video and Audio Encryption Application Diagram



PC Control Software

Supplied on 3.5“ disk, the TL2-Talk PC application and serial cable allows user configuration of the Viewlock II unit including:


Please contact Ovation Systems for more information.


ViewLock-Talk screen shot
ViewLock-Talk Screen Shot



Video Encryption Specification

Outline Specifications  
Operating temperature range -10 to +70ºC
Mechanical size 130 x 60 x 22 mm
Finish 220g (approx.)
Video input / output connectors BNC
DC power connector 2 pin Lemo
DC power requirement 6 to 32 V DC
Current consumption < 55 mA at 12 volts
EMC compliance European: EN55022:1994 class A
US: FCC part 15B class A
Standard accessories User guide, power leads, carrying case
Scrambling method Line cut and rotate
Number of cut points 256
Video standard supported PAL, SECAM & NTSC 625 & 525 lines
Video standards switching Auto sense
Video input / output 1 Vpp into 75R, ± 10 %
Digital sampling 8 bits @ 19.75 MHz
Video bandwidth 6Mhz @ -1dB, 8 MHz @ -3dB
Signal to noise > 55 dB (60dB typ) weighted
Differential gain < ± 4%
Differential phase < ± 5degrees
Luminance non-linearity (5 step) < ± 4%
Chrominance / luminance delay < 40nS
Lock up time < 0.5 second
Data line 22/334 (others programmable)
VBI Remains unscrambled
Scrambling method Digital audio sent over video
Audio input /output level (nominal) 0 dBU i.e. 2.2 V peak to peak (unbalanced)
Max audio input / output level (onset of clipping) +5 dBU (approximately 4 V peak to peak)
Audio input impedance 10kR
Audio output impedance 100R
Number of audio channels 1 or 2
Audio bandwidth (single channel mode) 100 Hz to 15 kHz (+1, -3 dB)
Audio bandwidth (dual channel mode) 100 Hz to 7.5 kHz (+1, -3 dB)
Signal to noise (wrt 2 Vpp input) >60 dB (weighted)
Distortion @ 0 dBU, 1 kHz < 2%
Video data lines used Lines 6 to 20 inclusive
Audio Compression Equivalent to 16 bit audio via adaptive differential pulse code modulation (ADPCM) giving 4 to 1 compression



Due to continual product development Ovation Systems reserve the right to change specifications without notice. E&OE.